Abdominal Imaging
ª Springer Science+Business Media New York 2014 Published online: 15 August 2014
Abdom Imaging (2015) 40:400–410 DOI: 10.1007/s00261-014-0216-8
Mimickers of neoplasm on abdominal and pelvic CT Ryan B. Schwope,1,2 Michael J. Reiter,1 Christopher J. Lisanti1,2 1
Department of Radiology, San Antonio Military Medical Center, 3551 Roger Brooke Drive, Fort Sam Houston, TX 78234, USA Department of Radiology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA 2
Abstract Purpose: The radiologist can encounter benign significant imaging findings on computed tomography that can be incorrectly interpreted as neoplasm. The authors review several benign findings and demonstrate several methods to differentiate these findings from more sinister pathology. Conclusion: It is imperative for the radiologist to be cognizant of and how to correctly identify mimickers of pathology so that unnecessary interventions and surgeries are avoided. Key words: Mimicker—Neoplasm—Abdomen— Pelvis—CT
There are several pitfalls in abdominopelvic computed tomography (CT) where misinterpretation of benign findings can result in unnecessary procedures and surgery with attendant morbidity and possibly mortality, and inaccurate tumor staging and thus incorrect therapies [1]. These imaging findings are frequently related to the following: mimickers related to prior surgery or treatment, anatomic variance, vascular entities, and sequelae of chronic disease processes (Table 1). The purpose of this article is to review benign imaging findings on CT that can be incorrectly interpreted as neoplasm, with selective examples from each aforementioned category. The authors then illustrate methods that can assist the radiologist in differentiating these mimickers from significant pathology including patient history, prior imaging, image manipulation and multiplanar reformations, multiphasic imaging, and other modalities. This article is not intended as an
Correspondence to: Ryan B. Schwope; email: [email protected]
extensive review, but instead addresses many topics that the authors feel may present as diagnostic dilemmas in everyday practice.
Mimickers related to prior surgery or treatment Dropped or spilled gallstones Laparoscopic cholecystectomy is one of the most common abdominal surgeries and preferred treatment for uncomplicated gallbladder disease. Compared to open cholecystectomy, the overall complication rate of laparoscopic cholecystectomy is less, although the rate of gallbladder perforation and gallstone spillage occurs more frequently in the laparoscopic procedure. This is because the field of view during laparoscopic cholecystectomy is smaller [2]. Spillage of gallstones into the abdominal cavity during laparoscopic cholecystectomy occurs in up to 30% of cases. Complications related to spilled gallstones occur in up to 6% of patients [2, 3]. Such complications, including adhesions, inflammatory reactions, abscesses, and peritonitis, occur more commonly if the choleliths are large, pigmented, numerous or fragmented, infected, or associated with infected bile [3]. Dropped gallstones can also potentially mimic peritoneal metastasis, particularly in the setting of gallstone-induced inflammatory or ‘‘foreign body’’ reaction, as reported in a case series by Atri et al. [4]. On CT, the density of the spilled gallstones can vary from hypodense to partially or completely calcified. Although not always present, the inflammatory reaction is demonstrated on CT as a hypodense lesion or halo, with or without peripheral enhancement and surrounding inflammatory change. Most of the dropped stones are located in the right abdomen, the majority in close proximity to the liver [4]. Personally the authors have found that careful windowing of the CT images can help illustrate faint radiodense choleliths within the
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Table 1. Mimickers of neoplasm categories, with examples of each as discussed in the article Post-surgical or treatment changes
Anatomic variance
Vascular entities
Sequelae of chronic disease processes
Dropped or spilled gallstones
Aberrant renal papilla
Extramedullary hematopoiesis
Failed renal allograft Inguinal mesh plug Ovarian transposition
Dilated cisterna chili Hypertrophied column of Bertin Differential cervical enhancement Focal fatty infiltration of the pancreas
Renal sinus aneurysm/ pseudoaneurysm and arteriovenous fistula Varices
Intrahepatic splenosis
Fig. 1. 51-year-old man with cirrhosis for hepatocellular carcinoma screening. A Axial contrast-enhanced CT demonstrates a heterogeneous lesion along the posterior right hepatic surface (arrow) with involvement of the diaphragm corresponding to an inflammatory response from dropped gall-
stones. Careful windowing and inspection of the lesion reveals multiple internal peripherally radiodense round objects. B Coronal contrast-enhanced CT prior to cholecystectomy demonstrates gallstones (arrow) which are identical in appearance to internal peripherally radiodense round objects in A.
hypodense lesion (Fig. 1A), consistent with gallstones within an inflammatory reaction. In addition, the patient’s history or postoperative changes indication prior cholecystectomy are integral clues to the radiologist, as well as prior CT imaging demonstrating if the gallstones were radiodense (Fig. 1B).
including carcinoid, gastrointestinal stromal tumor, sarcoma, or metastatic disease. Knowledge that the patient has undergone renal transplantation is crucial, although sometimes not provided in the patient history. Prior imaging showing a more normal-appearing renal transplant in the location of the failed renal allograft is also very helpful in identifying this mimicker (Fig. 2B).
Failed renal allograft Chronic rejection of a renal allograft occurs months to years after transplantation and occurs secondary to sclerosing vasculitis and extensive interstitial fibrosis. In the beginning stages of chronic rejection, the graft becomes enlarged and shows increased cortical thickness. Later on, the cortex thins and there can be mild hydronephrosis and urothelial thickening [5]. Patients with failed renal allografts either revert to chronic dialysis therapy or undergo retransplantation, with the failed allograft often left in situ [6]. Chronically rejected renal allografts are usually small and can demonstrate fatty replacement, hydronephrosis, infarcts, hemorrhage, and punctate or dense calcification (Fig. 2A) [6]. A failed renal allograft can masquerade as a pelvic neoplasm
Inguinal mesh plug Up to 0.3% of the population is affected by inguinal hernias, mostly men. Prosthetic meshes have significantly lowered the rate of recurrence after inguinal hernia repair. Depending on the inguinal hernia repair method chosen, a mesh plug can be used for reinforcement [7]. When identified on CT, inguinal findings after hernioplasty can have varying appearances depending on the procedure performed. Post-operative findings after inguinal hernia repair can manifest as a low density lesion, masquerading as an inguinal mass, or lymphadenopathy.
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Fig. 3. 57-year-old man with renal cell carcinoma. A Axial contrast-enhanced CT shows a lobular soft tissue attenuation lesion (arrow) at the internal ring of the left inguinal canal. B Coronal noncontrast CT demonstrates the conical morphology of the mesh plug (arrow), although inguinal findings after hernioplasty can have varying appearances.
found coronal imaging useful, demonstrating the conical morphology of the mesh plug (Fig. 3B). Surgical history is a crucial factor in differentiating post-hernioplasty findings with mesh from significant pathology. The radiologist can also look for inguinal region skin thickening suggestive of a surgical scar. Fig. 2. 64-year-old women status post renal transplant with abdominal pain. A Coronal CT without contrast shows a partially calcified left lower quadrant mass (arrow). A renal allograft is noted in the right iliac fossa (arrowhead). B Axial image from a contrast-enhanced CT from 2 years prior demonstrates a left iliac fossa renal allograft which is diminutive in size with peripheral calcification (arrow). These findings in conjunction with urothelial thickening are consistent with the earlier stages of chronic rejection.
One study described inguinal findings in post-hernioplasty patients as either ringlike with central fat attenuation, nodular with convex margins and homogenous CT attenuation greater than -20 HU (Fig. 3A), or feathery with an ill-defined shape and bands of mixed fat and higher attenuation [8]. The authors have anecdotally
Ovarian transposition Young patients who are to undergo radiation of the pelvis can have the ovaries surgically transposed out of the radiation field in order to preserve their function. The most common site of ovarian transposition is along the paracolic gutters, and anterior to the psoas muscle [9]. Either one or both ovaries can be transposed. The surgically transposed ovary may masquerade as a primary retroperitoneal neoplasm, lymphadenopathy, or tumor deposition, especially if no history is provided. CT features that can aid correct identification are surgical clips, expected morphologic features of ovaries, including physiologic cysts, and tracking the gonadal veins to the ovaries [10]. Contralateral ovarian transposition and a clinical history of pelvic malignancy are also useful (Fig. 4).
R. B. Schwope et al.: Neoplasm on abdominal and pelvic CT
Fig. 4. 39-year-old woman with cervical cancer. A, B Axial images from a CT with intravenous contrast demonstrate a soft tissue attenuation lesion (arrow, A) in the right paracolic gutter. A similar finding with an adjacent surgical clip is present in the left paracolic gutter (arrow, B) aiding in the diagnosis of ovarian transposition.
Mimickers related to anatomic variance
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Fig. 5. 29-year-old man with hematuria. A Coronal excretory phase CT shows a small enhancing filling defect (arrow) arising from an infundibulum. B Careful windowing of an axial excretory phase CT image demonstrates a blush (arrow) within the renal parenchyma abutting the filling defect/papilla, identical to that of the normal papillary blush (arrowhead). This finding was stable over several years.
Aberrant renal papilla Aberrant or ectopic papilla has been defined as a normal papilla that projects directly into the infundibulum, without a surrounding calyx [11]. As it does appear as a filling defect on CT urography, an aberrant renal papilla can masquerade as urothelial neoplasm. Although its radiologic appearance has been described on intravenous urography as a sharply marginated, ovoid, immobile filling defect with a surrounding halo of contrast [12], there is a relative paucity of information regarding the CT appearance of aberrant renal papillae. The authors speculate that the blush of enhancement within the renal parenchyma adjacent to a round filling defect, identical to that of the normal papillary blush, can aid in the diagnosis of this entity. A narrow window can help demonstrate this finding (Fig. 5). If ureteroscopy is deferred, confirmation can be made with comparisons or follow-up. The absence of hematuria can also
aid in differentiating an aberrant papilla from urothelial neoplasm.
Dilated cisterna chyli The cisterna chyli is a dilated lymphatic sac that is retrocrural in position, most commonly at L1–L2 and immediately to the right of the aorta. Typically, the cisterna chyli receives lymphatic drainage from two lumbar trunks and an intestinal trunk. The lymph continues cephalad from the cisterna chyli into the thoracic duct, ultimately and usually draining into the internal jugular vein. Although variable in appearance, the cisterna chyli classically has a tubular shape [13]. Delayed enhancement has been noted of the cisterna chyli 5 minutes or greater after intravenous contrast administration on MRI [14]. The cisterna chyli has been reportedly
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A dilated cisterna chyli can potentially mimic retrocrural lymphadenopathy (Fig. 6A). Multiplanar reformations can depict the tubular morphology of the dilated lymph channel, often best appreciated on coronal imaging (Fig. 6B). Hounsfield unit interrogation demonstrating fluid attenuation can be helpful. Although lymph nodes with necrosis can also have fluid density centers, the walls of necrotic lymph nodes are typically thick and irregular. MRI can assist is demonstrating the cystic nature of the cisterna chyli, and its continuity with the thoracic duct on T2-weighted imaging (Fig. 6C). Stability can also help with the diagnosis, although size changes can occur between studies due to phase of respiration, hydration, and lower thoracic duct peristalsis [17].
Hypertrophied column of Bertin A column of Bertin is cortical tissue between pyramids that projects in to the renal sinus. This tissue can hypertrophy, resulting in mass effect upon the renal sinus and an unusual configuration of the calyces [18]. On unenhanced CT, this hypertrophied renal tissue can appear as a solid tumor (Fig. 7A). A column of Bertin can be confirmed after intravenous contrast administration as it will demonstrate enhancement similar to surrounding renal parenchyma (Fig. 7B–D).
Differential cervical enhancement
Fig. 6. 64-year-old woman with lung cancer. A Axial contrast-enhanced CT shows a round structure of fluid attenuation with imperceptible walls (arrow) within the right retrocrural region. B Coronal contrast-enhanced CT shows the classic tubular morphology (arrow) of the cisterna chyli. C Coronal T2-weighted MRI from a different patient demonstrates the cystic nature of the cisterna chyli and its continuity (arrow) with the thoracic duct.
visualized in 1.7% and 15% of patients on CT and MRI, respectively, and has an average size of 7.4 mm in the anteroposterior dimension and 7 mm in the transverse dimension [14, 15]. Dilatation can occur secondary to lymphatic damage from prior gastroesophageal or retroperitoneal surgery, uncompensated cirrhosis, hypoalbuminemia, lymphangioleiomyomatosis, elevated central venous pressure, and pancreatobiliary obstruction [16].
The cervix can demonstrate delayed enhancement in comparison with the uterus, appearing decreased in attenuation on CT, depending on the phase of imaging. This differential enhancement of the cervix may cause normal cervical tissue to mimic a mass. The normal endocervical canal should not be obliterated or effaced, and in continuity with the endometrial canal. Conversely, a cervical mass may result in dilatation of the endometrial canal due to obstruction. Multiplanar reformations can be useful in identifying normal cervix. Findings related to differential enhancement result in a distinct demarcation between the hypoenhancing cervix/lower uterine segment and enhancing myometrium, best seen on sagittal images (Fig. 8) [19]. Clinical information such as the absence of vaginal bleeding, and a normal speculum exam and Pap smear can confirm that the imaging findings are related to differential cervical enhancement.
Focal fatty infiltration of the pancreas Focal fatty infiltration of the pancreas most commonly occurs in the anterior aspect of the pancreatic head. This entity is frequently seen in the elderly and obese
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Fig. 7. 59-year-old woman with a suspicious renal lesion on ultrasound (not shown). Axial images from a noncontrast CT (A), during the corticomedullary phase (B), and during the nephrographic phase (C) shows a soft tissue density lesion projecting into the right renal sinus (arrows). The enhancement of the lesion is similar to that of renal parenchyma. D Axial excretory phase CT shows a calyx (arrow) arising within this lesion further confirming the lesion as hypertrophied renal parenchyma.
population, and associated with diabetes mellitus, chronic pancreatitis, hepatic disease, dietary deficiencies, viral infection, and steroids. On contrast-enhanced CT, the focal fatty infiltration appears as a vague area of hypoenhancement, similar to that of pancreatic adenocarcinoma. A variation of this finding is invagination of small foci of retroperitoneal fat into the pancreatic parenchyma which on CT can mimic small cystic pancreatic neoplasms, including side-branch intraductal papillary mucinous neoplasm or serous cystadenoma. Focal fatty infiltration often is ovoid or triangular in morphology with linear margins (Fig. 9A), and there is no associated mass effect or pancreatic duct dilatation as seen with pancreatic neoplasm. In- and opposed-phase T1-weighted gradient echo MR imaging can confirm the presence of fat as demonstrated by loss of signal loss in the region of focal fatty infiltration due to chemical shift (Fig. 9B, C) [20, 21]. The use of T2-weighted MR
imaging can show the non-cystic nature of this mimicker, thus differentiating it from cystic neoplasms.
Vascular entities Renal sinus aneurysm/pseudoaneurysm and arteriovenous fistula Renal artery aneurysms/pseudoaneurysms and arteriovenous communications (malformations and fistulae) can manifest as a solid lesion if intraparenchymal or in the renal sinus. The most common cause of renal artery aneurysms is atherosclerosis. Biopsy is the most common cause of acquired ateriovenous communications (fistulae), which can manifest with hypertension, hematuria, high-output cardiac failure, or abdominal pain [22]. Careful lesion evaluation on multiphasic imaging, searching for tortuous vessels and an early draining vein (Fig. 10), can help delineate the vascular nature of a
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Fig. 8. 38-year-old woman with lower abdominal pain. A Axial contrast-enhanced CT demonstrates mass-like hypoenhancement of the cervix (arrow). B Sagittal contrastenhanced CT illustrates the sharp demarcation at the cervicouterine junction (arrow), thus differentiating this differential enhancement from a cervical mass. In addition, there is continuity of the endometrial canal with the endocervical canal (arrowhead), neither of which are dilated or effaced.
renal sinus aneurysm and arteriovenous fistula. Ultrasound can exclude a solid mass by demonstration of an anechoic lesion with internal color flow with arterial waveform on pulsed and Doppler interrogation. Multiphasic gadolinium-enhanced MRI can confirm the vascular etiology of this lesion. If the patient cannot receive gadolinium, unenhanced MRI can suggest the vascular etiology of this lesion by the presence of flow-related
Fig. 9. 49-year-old woman with 3 months duration of midepigastric pain. A Axial image from a CT with intravenous contrast shows a hypoenhancing region in the anterior pancreatic head, which has a linear margin (arrowheads). Axial in-phase (B) and out-of-phase (C) MR images show diffuse loss of signal of this lesion on the out-of-phase image (arrow, C) consistent with focal fatty infiltration. No malignancy was identified upon fine needle aspiration of this lesion via endoscopic ultrasound access (not shown).
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Fig. 10. 37-year-old woman with hematuria and remote history of random right renal biopsy. A Axial contrast-enhanced CT during the arterial phase shows an enhancing right renal sinus lesion (arrow). B Coronal contrast-enhanced CT image during the arterial phase shows early
filling of a vein (arrow) consistent with a renal sinus pseudoaneurysm and arteriovenous fistula. C Image from selective catheter angiography of the right renal artery confirms the pseudoaneurysm (arrow) and early draining vein (arrowhead).
signal voids, although this should be interpreted with caution and correlated with other modalities as calcification can also result in signal voids [18]. A history of percutaneous renal sampling can aid in this diagnosis. The definitive procedure for diagnosing and treatment of this vascular lesion is conventional renal angiography.
occlusion. Varices can also occur along the bile ducts in this setting [23]. These collateral vessels result in gallbladder wall thickening and potentially mimic cholecystitis and neoplasm. Portal hypertension can also result in periadrenal and adrenal portosytemic collaterals via the left inferior phrenic vein. These vessels can mimic an adrenal lesion when closely opposed to the adrenal gland [24]. Pelvic varices are more common in women and are usually related to dilatation and tortuosity of the parauterine and ovarian veins [25]. On CT, pelvic varices can be mistaken for soft tissue masses, lymphadenopathy, or cysts. This misdiagnosis of varices can occur if the tubular morphology of the lesions is not recognized, or if the
Varices Varices are dilated vessels and occur in various locations throughout the body. Gallbladder varices are a manifestation of portal biliopathy and occur in the setting of portal hypertension, particularly with extrahepatic portal vein
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Sequelae of chronic disease processes Extramedullary hematopoesis Commonly found in patients with chronic myeloproliferative disorders, extramedullary hematopoiesis (EMH) is a response to failed bone marrow erythropoiesis. EMH occurs most often in the spleen, liver, and occasionally lymph nodes. The classic imaging finding is hepatosplenomegaly. Other organ involvement within the abdomen and pelvis include, but is not limited to, the kidneys and mesentery [26]. When uniformly enhancing, these masses can mimic lymphoma. Masses of hematopoietic elements can also involve the retrorectal region, masquerading as a chordoma or other presacral lesions (Fig. 12A). Knowledge of the patient’s clinical history is paramount to avoid misdiagnosis. Resultant marrow changes of chronic myeloproliferative disorders, manifested as osteosclerosis on imaging, can be helpful. Masses secondary to EMH can contain macroscopic fat and are classic for this diagnosis, relating to fatty conversion similarly seen in bone marrow (Fig. 12B, C) [27, 28]. Evaluation for EMH with bone marrow imaging agents, such as Tc-99m sulfur colloid and In-111 chloride, has been shown useful as these agents demonstrate uptake by reticuloendothelial and hematopoietic cells, respectively [29]. Fig. 11. 64-year-old man with cirrhosis for hepatocellular carcinoma screening. A Axial contrast-enhanced CT during the arterial phase demonstrates mixed attenuation wall thickening of the gallbladder (arrow). B Axial contrast-enhanced CT during the portal venous phase show tubular enhancing structures (arrow) in the gallbladder wall consistent with varices.
lesions are imaged without contrast or during the arterial phase when the vessels are not opacified. Multiphasic CT will demonstrate the expected enhancement of portosystemic collaterals in the portal venous phase (Fig. 11), and scrutiny of the lesion can illustrate its connection to adjacent collateral vessels. Coronal and sagittal reformations can assist in depicting the tubular morphology of these vascular lesions. Ultrasound can help reveal the portal venous origin of these pseudo-lesions by demonstrating tubular anechoic structures on grayscale imaging with corresponding internal color flow with a monophasic waveform on color and pulsed Doppler interrogation. The presence of flow-related signal voids on MRI can also be useful in establishing the vascular nature of these findings.
Intrahepatic splenosis Splenosis is defined as autotransplantation of splenic tissue after rupture of the splenic capsule, usually from prior trauma. The splenic tissue can implant in various locations, the most common of which are the serosal surface of the small intestine and greater omentum, with intrahepatic splenosis rare [30, 31]. When the liver is involved, the splenosis is not truly intrahepatic as the splenic tissue implants on the serosal surface. On CT imaging, there is usually one or more homogenous, solid, non-calcified nodule (Fig. 13A). This entity is notorious for mimicking benign and malignant neoplastic processes. Arterial phase CT imaging can help in diagnosing splenosis as splenic tissue usually demonstrates characteristic arciform enhancement in this phase. Tc-99m-labeled heat-denatured erythrocytes or Tc-99m sulfur colloid nuclear medicine studies will show uptake in the residual splenic tissue (Fig. 13B), although the former is more specific [32]. A history of prior trauma is useful knowledge.
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Fig. 12. 66-year-old man with myelofibrosis. A Axial contrast-enhanced CT shows a retrorectal (presacral) mass (arrow). B Coronal contrast-enhanced CT shows additional masses in the upper abdomen (arrow and arrowhead). The larger mass in the right upper quadrant (arrow) contains fat
density, which can be seen with lesions containing hematopoietic elements. C Coronal CT image with bone algorithm demonstrates diffusely sclerotic osseous structures compatible with the provided history of a myeloproliferative disorder.
Fig. 13. 52-year-old woman with abdominal pain and a remote history of exploratory laparotomy. A Axial contrastenhanced CT shows a round enhancing lesion (arrow) along the posterolateral aspect of the left lobe of the liver. The
spleen is absent. B Axial image from a Tc-99m-labeled heatdenatured RBC nuclear medicine scan shows uptake in this lesion (arrow), consistent with splenic tissue.
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Conclusion Radiologists must be aware of certain entities that can mimic neoplasm on CT of the abdomen and pelvis and know how to avoid misdiagnosis, so that additional tests and potentially fatal intervention can be avoided. Acknowledgments. Christopher J. Lisanti receives royalties from Lippincott, Williams and Wilkins.
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15. Smith TR, Grigoropoulos J (2002) The cisterna chili: incidence and characteristics on CT. Clin Imaging 26:18–22 16. Arrive´ L, Azizi L, Lewin M, et al. (2007) MR lymphography of abdominal and retroperitoneal lymphatic vessels. AJR 189(5):1051–1058 17. Gollub MJ, Castellino RA (1996) The cisterna chyli: a potential mimic of retrocrural lymphadenopathy on CT scans. Radiology 199(2):477–480 18. Bhatt S, MacLennan G, Dogra V (2007) Renal pseudotumors. AJR 188(5):1380–1387 19. Yitta S, Hecht EM, Mausner EV, et al. (2011) Normal or abnormal? Demystifying uterine and cervical contrast enhancement at multidetector CT. Radiographics 31(3):647–661 20. Kim HJ, Byun JH, Park SH, et al. (2007) Focal fatty replacement of the pancreas: usefulness of chemical shift MRI. AJR 188(2):429– 432 21. Isserow JA, Siegelman ES, Mammone J (1999) Focal fatty infiltration of the pancreas: MR characterization with chemical shift imaging. AJR 173(5):1263–1265 22. Rha SE, Byun JY, Jung SE, et al. (2004) The renal sinus: pathologic spectrum and multimodality imaging approach. Radiographics 24(Suppl 1):S117–S131 23. Shin SM, Kim S, Lee JW, et al. (2007) Biliary abnormalities associated with portal biliopathy: evaluation on MR cholangiography. AJR 188(4):W341–W347 24. Brady TM, Gross BH, Glazer GM, et al. (1985) Adrenal pseudomasses due to varices: angiographic-CT-MRI-pathologic correlations. AJR 145(2):301–304 25. Vahidid K, Joe BN, Meng M, et al. (2007) Review of atypical pelvic masses on CT and MRI: expanding the differential diagnosis. Clin Imaging 31:406–413 26. Georgiades CS, Neyman EG, Francis IR, et al. (2002) Typical and atypical presentations of extramedullary hemopoiesis. AJR 179(5): 1239–1243 27. Gupta P, Naran A, Auh YH, et al. (2004) Focal intrahepatic extramedullary hematopoiesis presenting as fatty lesions. AJR 182(4):1031–1032 28. Surabhi VR, Menias C, Prasad SR, et al. (2008) Neoplastic and non-neoplastic proliferative disorders of the perirenal space: crosssectional imaging findings. Radiographics 28(4):1005–1017 29. Choi H, David CL, Katz RL, et al. (2004) Case 69: extramedullary hematopoiesis. Radiology 231(1):52–56 30. Fleming CR, Dickson ER, Harrison EG (1976) Splenosis: autotransplantation of splenic tissue. Am J Med 61:414–419 31. Pumberger W, Wiesbauer P, Leitha T (2001) Splenosis mimicking tumor recurrence in renal cell carcinoma: detection on selective spleen scintigraphy. J Pediatr Surg 36:1089–1091 32. Malik UF, Martin MR, Patel R, et al. (2010) Parenchymal thoracic splenosis: history and nuclear imaging without invasive procedures may provide diagnosis. J Clin Med Res 2(4):180–184
ª Springer Science+Business Media New York 2014 Published online: 15 August 2014
Abdom Imaging (2015) 40:400–410 DOI: 10.1007/s00261-014-0216-8
Mimickers of neoplasm on abdominal and pelvic CT Ryan B. Schwope,1,2 Michael J. Reiter,1 Christopher J. Lisanti1,2 1
Department of Radiology, San Antonio Military Medical Center, 3551 Roger Brooke Drive, Fort Sam Houston, TX 78234, USA Department of Radiology, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814, USA 2
Abstract Purpose: The radiologist can encounter benign significant imaging findings on computed tomography that can be incorrectly interpreted as neoplasm. The authors review several benign findings and demonstrate several methods to differentiate these findings from more sinister pathology. Conclusion: It is imperative for the radiologist to be cognizant of and how to correctly identify mimickers of pathology so that unnecessary interventions and surgeries are avoided. Key words: Mimicker—Neoplasm—Abdomen— Pelvis—CT
There are several pitfalls in abdominopelvic computed tomography (CT) where misinterpretation of benign findings can result in unnecessary procedures and surgery with attendant morbidity and possibly mortality, and inaccurate tumor staging and thus incorrect therapies [1]. These imaging findings are frequently related to the following: mimickers related to prior surgery or treatment, anatomic variance, vascular entities, and sequelae of chronic disease processes (Table 1). The purpose of this article is to review benign imaging findings on CT that can be incorrectly interpreted as neoplasm, with selective examples from each aforementioned category. The authors then illustrate methods that can assist the radiologist in differentiating these mimickers from significant pathology including patient history, prior imaging, image manipulation and multiplanar reformations, multiphasic imaging, and other modalities. This article is not intended as an
Correspondence to: Ryan B. Schwope; email: [email protected]
extensive review, but instead addresses many topics that the authors feel may present as diagnostic dilemmas in everyday practice.
Mimickers related to prior surgery or treatment Dropped or spilled gallstones Laparoscopic cholecystectomy is one of the most common abdominal surgeries and preferred treatment for uncomplicated gallbladder disease. Compared to open cholecystectomy, the overall complication rate of laparoscopic cholecystectomy is less, although the rate of gallbladder perforation and gallstone spillage occurs more frequently in the laparoscopic procedure. This is because the field of view during laparoscopic cholecystectomy is smaller [2]. Spillage of gallstones into the abdominal cavity during laparoscopic cholecystectomy occurs in up to 30% of cases. Complications related to spilled gallstones occur in up to 6% of patients [2, 3]. Such complications, including adhesions, inflammatory reactions, abscesses, and peritonitis, occur more commonly if the choleliths are large, pigmented, numerous or fragmented, infected, or associated with infected bile [3]. Dropped gallstones can also potentially mimic peritoneal metastasis, particularly in the setting of gallstone-induced inflammatory or ‘‘foreign body’’ reaction, as reported in a case series by Atri et al. [4]. On CT, the density of the spilled gallstones can vary from hypodense to partially or completely calcified. Although not always present, the inflammatory reaction is demonstrated on CT as a hypodense lesion or halo, with or without peripheral enhancement and surrounding inflammatory change. Most of the dropped stones are located in the right abdomen, the majority in close proximity to the liver [4]. Personally the authors have found that careful windowing of the CT images can help illustrate faint radiodense choleliths within the
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Table 1. Mimickers of neoplasm categories, with examples of each as discussed in the article Post-surgical or treatment changes
Anatomic variance
Vascular entities
Sequelae of chronic disease processes
Dropped or spilled gallstones
Aberrant renal papilla
Extramedullary hematopoiesis
Failed renal allograft Inguinal mesh plug Ovarian transposition
Dilated cisterna chili Hypertrophied column of Bertin Differential cervical enhancement Focal fatty infiltration of the pancreas
Renal sinus aneurysm/ pseudoaneurysm and arteriovenous fistula Varices
Intrahepatic splenosis
Fig. 1. 51-year-old man with cirrhosis for hepatocellular carcinoma screening. A Axial contrast-enhanced CT demonstrates a heterogeneous lesion along the posterior right hepatic surface (arrow) with involvement of the diaphragm corresponding to an inflammatory response from dropped gall-
stones. Careful windowing and inspection of the lesion reveals multiple internal peripherally radiodense round objects. B Coronal contrast-enhanced CT prior to cholecystectomy demonstrates gallstones (arrow) which are identical in appearance to internal peripherally radiodense round objects in A.
hypodense lesion (Fig. 1A), consistent with gallstones within an inflammatory reaction. In addition, the patient’s history or postoperative changes indication prior cholecystectomy are integral clues to the radiologist, as well as prior CT imaging demonstrating if the gallstones were radiodense (Fig. 1B).
including carcinoid, gastrointestinal stromal tumor, sarcoma, or metastatic disease. Knowledge that the patient has undergone renal transplantation is crucial, although sometimes not provided in the patient history. Prior imaging showing a more normal-appearing renal transplant in the location of the failed renal allograft is also very helpful in identifying this mimicker (Fig. 2B).
Failed renal allograft Chronic rejection of a renal allograft occurs months to years after transplantation and occurs secondary to sclerosing vasculitis and extensive interstitial fibrosis. In the beginning stages of chronic rejection, the graft becomes enlarged and shows increased cortical thickness. Later on, the cortex thins and there can be mild hydronephrosis and urothelial thickening [5]. Patients with failed renal allografts either revert to chronic dialysis therapy or undergo retransplantation, with the failed allograft often left in situ [6]. Chronically rejected renal allografts are usually small and can demonstrate fatty replacement, hydronephrosis, infarcts, hemorrhage, and punctate or dense calcification (Fig. 2A) [6]. A failed renal allograft can masquerade as a pelvic neoplasm
Inguinal mesh plug Up to 0.3% of the population is affected by inguinal hernias, mostly men. Prosthetic meshes have significantly lowered the rate of recurrence after inguinal hernia repair. Depending on the inguinal hernia repair method chosen, a mesh plug can be used for reinforcement [7]. When identified on CT, inguinal findings after hernioplasty can have varying appearances depending on the procedure performed. Post-operative findings after inguinal hernia repair can manifest as a low density lesion, masquerading as an inguinal mass, or lymphadenopathy.
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Fig. 3. 57-year-old man with renal cell carcinoma. A Axial contrast-enhanced CT shows a lobular soft tissue attenuation lesion (arrow) at the internal ring of the left inguinal canal. B Coronal noncontrast CT demonstrates the conical morphology of the mesh plug (arrow), although inguinal findings after hernioplasty can have varying appearances.
found coronal imaging useful, demonstrating the conical morphology of the mesh plug (Fig. 3B). Surgical history is a crucial factor in differentiating post-hernioplasty findings with mesh from significant pathology. The radiologist can also look for inguinal region skin thickening suggestive of a surgical scar. Fig. 2. 64-year-old women status post renal transplant with abdominal pain. A Coronal CT without contrast shows a partially calcified left lower quadrant mass (arrow). A renal allograft is noted in the right iliac fossa (arrowhead). B Axial image from a contrast-enhanced CT from 2 years prior demonstrates a left iliac fossa renal allograft which is diminutive in size with peripheral calcification (arrow). These findings in conjunction with urothelial thickening are consistent with the earlier stages of chronic rejection.
One study described inguinal findings in post-hernioplasty patients as either ringlike with central fat attenuation, nodular with convex margins and homogenous CT attenuation greater than -20 HU (Fig. 3A), or feathery with an ill-defined shape and bands of mixed fat and higher attenuation [8]. The authors have anecdotally
Ovarian transposition Young patients who are to undergo radiation of the pelvis can have the ovaries surgically transposed out of the radiation field in order to preserve their function. The most common site of ovarian transposition is along the paracolic gutters, and anterior to the psoas muscle [9]. Either one or both ovaries can be transposed. The surgically transposed ovary may masquerade as a primary retroperitoneal neoplasm, lymphadenopathy, or tumor deposition, especially if no history is provided. CT features that can aid correct identification are surgical clips, expected morphologic features of ovaries, including physiologic cysts, and tracking the gonadal veins to the ovaries [10]. Contralateral ovarian transposition and a clinical history of pelvic malignancy are also useful (Fig. 4).
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Fig. 4. 39-year-old woman with cervical cancer. A, B Axial images from a CT with intravenous contrast demonstrate a soft tissue attenuation lesion (arrow, A) in the right paracolic gutter. A similar finding with an adjacent surgical clip is present in the left paracolic gutter (arrow, B) aiding in the diagnosis of ovarian transposition.
Mimickers related to anatomic variance
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Fig. 5. 29-year-old man with hematuria. A Coronal excretory phase CT shows a small enhancing filling defect (arrow) arising from an infundibulum. B Careful windowing of an axial excretory phase CT image demonstrates a blush (arrow) within the renal parenchyma abutting the filling defect/papilla, identical to that of the normal papillary blush (arrowhead). This finding was stable over several years.
Aberrant renal papilla Aberrant or ectopic papilla has been defined as a normal papilla that projects directly into the infundibulum, without a surrounding calyx [11]. As it does appear as a filling defect on CT urography, an aberrant renal papilla can masquerade as urothelial neoplasm. Although its radiologic appearance has been described on intravenous urography as a sharply marginated, ovoid, immobile filling defect with a surrounding halo of contrast [12], there is a relative paucity of information regarding the CT appearance of aberrant renal papillae. The authors speculate that the blush of enhancement within the renal parenchyma adjacent to a round filling defect, identical to that of the normal papillary blush, can aid in the diagnosis of this entity. A narrow window can help demonstrate this finding (Fig. 5). If ureteroscopy is deferred, confirmation can be made with comparisons or follow-up. The absence of hematuria can also
aid in differentiating an aberrant papilla from urothelial neoplasm.
Dilated cisterna chyli The cisterna chyli is a dilated lymphatic sac that is retrocrural in position, most commonly at L1–L2 and immediately to the right of the aorta. Typically, the cisterna chyli receives lymphatic drainage from two lumbar trunks and an intestinal trunk. The lymph continues cephalad from the cisterna chyli into the thoracic duct, ultimately and usually draining into the internal jugular vein. Although variable in appearance, the cisterna chyli classically has a tubular shape [13]. Delayed enhancement has been noted of the cisterna chyli 5 minutes or greater after intravenous contrast administration on MRI [14]. The cisterna chyli has been reportedly
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A dilated cisterna chyli can potentially mimic retrocrural lymphadenopathy (Fig. 6A). Multiplanar reformations can depict the tubular morphology of the dilated lymph channel, often best appreciated on coronal imaging (Fig. 6B). Hounsfield unit interrogation demonstrating fluid attenuation can be helpful. Although lymph nodes with necrosis can also have fluid density centers, the walls of necrotic lymph nodes are typically thick and irregular. MRI can assist is demonstrating the cystic nature of the cisterna chyli, and its continuity with the thoracic duct on T2-weighted imaging (Fig. 6C). Stability can also help with the diagnosis, although size changes can occur between studies due to phase of respiration, hydration, and lower thoracic duct peristalsis [17].
Hypertrophied column of Bertin A column of Bertin is cortical tissue between pyramids that projects in to the renal sinus. This tissue can hypertrophy, resulting in mass effect upon the renal sinus and an unusual configuration of the calyces [18]. On unenhanced CT, this hypertrophied renal tissue can appear as a solid tumor (Fig. 7A). A column of Bertin can be confirmed after intravenous contrast administration as it will demonstrate enhancement similar to surrounding renal parenchyma (Fig. 7B–D).
Differential cervical enhancement
Fig. 6. 64-year-old woman with lung cancer. A Axial contrast-enhanced CT shows a round structure of fluid attenuation with imperceptible walls (arrow) within the right retrocrural region. B Coronal contrast-enhanced CT shows the classic tubular morphology (arrow) of the cisterna chyli. C Coronal T2-weighted MRI from a different patient demonstrates the cystic nature of the cisterna chyli and its continuity (arrow) with the thoracic duct.
visualized in 1.7% and 15% of patients on CT and MRI, respectively, and has an average size of 7.4 mm in the anteroposterior dimension and 7 mm in the transverse dimension [14, 15]. Dilatation can occur secondary to lymphatic damage from prior gastroesophageal or retroperitoneal surgery, uncompensated cirrhosis, hypoalbuminemia, lymphangioleiomyomatosis, elevated central venous pressure, and pancreatobiliary obstruction [16].
The cervix can demonstrate delayed enhancement in comparison with the uterus, appearing decreased in attenuation on CT, depending on the phase of imaging. This differential enhancement of the cervix may cause normal cervical tissue to mimic a mass. The normal endocervical canal should not be obliterated or effaced, and in continuity with the endometrial canal. Conversely, a cervical mass may result in dilatation of the endometrial canal due to obstruction. Multiplanar reformations can be useful in identifying normal cervix. Findings related to differential enhancement result in a distinct demarcation between the hypoenhancing cervix/lower uterine segment and enhancing myometrium, best seen on sagittal images (Fig. 8) [19]. Clinical information such as the absence of vaginal bleeding, and a normal speculum exam and Pap smear can confirm that the imaging findings are related to differential cervical enhancement.
Focal fatty infiltration of the pancreas Focal fatty infiltration of the pancreas most commonly occurs in the anterior aspect of the pancreatic head. This entity is frequently seen in the elderly and obese
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Fig. 7. 59-year-old woman with a suspicious renal lesion on ultrasound (not shown). Axial images from a noncontrast CT (A), during the corticomedullary phase (B), and during the nephrographic phase (C) shows a soft tissue density lesion projecting into the right renal sinus (arrows). The enhancement of the lesion is similar to that of renal parenchyma. D Axial excretory phase CT shows a calyx (arrow) arising within this lesion further confirming the lesion as hypertrophied renal parenchyma.
population, and associated with diabetes mellitus, chronic pancreatitis, hepatic disease, dietary deficiencies, viral infection, and steroids. On contrast-enhanced CT, the focal fatty infiltration appears as a vague area of hypoenhancement, similar to that of pancreatic adenocarcinoma. A variation of this finding is invagination of small foci of retroperitoneal fat into the pancreatic parenchyma which on CT can mimic small cystic pancreatic neoplasms, including side-branch intraductal papillary mucinous neoplasm or serous cystadenoma. Focal fatty infiltration often is ovoid or triangular in morphology with linear margins (Fig. 9A), and there is no associated mass effect or pancreatic duct dilatation as seen with pancreatic neoplasm. In- and opposed-phase T1-weighted gradient echo MR imaging can confirm the presence of fat as demonstrated by loss of signal loss in the region of focal fatty infiltration due to chemical shift (Fig. 9B, C) [20, 21]. The use of T2-weighted MR
imaging can show the non-cystic nature of this mimicker, thus differentiating it from cystic neoplasms.
Vascular entities Renal sinus aneurysm/pseudoaneurysm and arteriovenous fistula Renal artery aneurysms/pseudoaneurysms and arteriovenous communications (malformations and fistulae) can manifest as a solid lesion if intraparenchymal or in the renal sinus. The most common cause of renal artery aneurysms is atherosclerosis. Biopsy is the most common cause of acquired ateriovenous communications (fistulae), which can manifest with hypertension, hematuria, high-output cardiac failure, or abdominal pain [22]. Careful lesion evaluation on multiphasic imaging, searching for tortuous vessels and an early draining vein (Fig. 10), can help delineate the vascular nature of a
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Fig. 8. 38-year-old woman with lower abdominal pain. A Axial contrast-enhanced CT demonstrates mass-like hypoenhancement of the cervix (arrow). B Sagittal contrastenhanced CT illustrates the sharp demarcation at the cervicouterine junction (arrow), thus differentiating this differential enhancement from a cervical mass. In addition, there is continuity of the endometrial canal with the endocervical canal (arrowhead), neither of which are dilated or effaced.
renal sinus aneurysm and arteriovenous fistula. Ultrasound can exclude a solid mass by demonstration of an anechoic lesion with internal color flow with arterial waveform on pulsed and Doppler interrogation. Multiphasic gadolinium-enhanced MRI can confirm the vascular etiology of this lesion. If the patient cannot receive gadolinium, unenhanced MRI can suggest the vascular etiology of this lesion by the presence of flow-related
Fig. 9. 49-year-old woman with 3 months duration of midepigastric pain. A Axial image from a CT with intravenous contrast shows a hypoenhancing region in the anterior pancreatic head, which has a linear margin (arrowheads). Axial in-phase (B) and out-of-phase (C) MR images show diffuse loss of signal of this lesion on the out-of-phase image (arrow, C) consistent with focal fatty infiltration. No malignancy was identified upon fine needle aspiration of this lesion via endoscopic ultrasound access (not shown).
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Fig. 10. 37-year-old woman with hematuria and remote history of random right renal biopsy. A Axial contrast-enhanced CT during the arterial phase shows an enhancing right renal sinus lesion (arrow). B Coronal contrast-enhanced CT image during the arterial phase shows early
filling of a vein (arrow) consistent with a renal sinus pseudoaneurysm and arteriovenous fistula. C Image from selective catheter angiography of the right renal artery confirms the pseudoaneurysm (arrow) and early draining vein (arrowhead).
signal voids, although this should be interpreted with caution and correlated with other modalities as calcification can also result in signal voids [18]. A history of percutaneous renal sampling can aid in this diagnosis. The definitive procedure for diagnosing and treatment of this vascular lesion is conventional renal angiography.
occlusion. Varices can also occur along the bile ducts in this setting [23]. These collateral vessels result in gallbladder wall thickening and potentially mimic cholecystitis and neoplasm. Portal hypertension can also result in periadrenal and adrenal portosytemic collaterals via the left inferior phrenic vein. These vessels can mimic an adrenal lesion when closely opposed to the adrenal gland [24]. Pelvic varices are more common in women and are usually related to dilatation and tortuosity of the parauterine and ovarian veins [25]. On CT, pelvic varices can be mistaken for soft tissue masses, lymphadenopathy, or cysts. This misdiagnosis of varices can occur if the tubular morphology of the lesions is not recognized, or if the
Varices Varices are dilated vessels and occur in various locations throughout the body. Gallbladder varices are a manifestation of portal biliopathy and occur in the setting of portal hypertension, particularly with extrahepatic portal vein
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Sequelae of chronic disease processes Extramedullary hematopoesis Commonly found in patients with chronic myeloproliferative disorders, extramedullary hematopoiesis (EMH) is a response to failed bone marrow erythropoiesis. EMH occurs most often in the spleen, liver, and occasionally lymph nodes. The classic imaging finding is hepatosplenomegaly. Other organ involvement within the abdomen and pelvis include, but is not limited to, the kidneys and mesentery [26]. When uniformly enhancing, these masses can mimic lymphoma. Masses of hematopoietic elements can also involve the retrorectal region, masquerading as a chordoma or other presacral lesions (Fig. 12A). Knowledge of the patient’s clinical history is paramount to avoid misdiagnosis. Resultant marrow changes of chronic myeloproliferative disorders, manifested as osteosclerosis on imaging, can be helpful. Masses secondary to EMH can contain macroscopic fat and are classic for this diagnosis, relating to fatty conversion similarly seen in bone marrow (Fig. 12B, C) [27, 28]. Evaluation for EMH with bone marrow imaging agents, such as Tc-99m sulfur colloid and In-111 chloride, has been shown useful as these agents demonstrate uptake by reticuloendothelial and hematopoietic cells, respectively [29]. Fig. 11. 64-year-old man with cirrhosis for hepatocellular carcinoma screening. A Axial contrast-enhanced CT during the arterial phase demonstrates mixed attenuation wall thickening of the gallbladder (arrow). B Axial contrast-enhanced CT during the portal venous phase show tubular enhancing structures (arrow) in the gallbladder wall consistent with varices.
lesions are imaged without contrast or during the arterial phase when the vessels are not opacified. Multiphasic CT will demonstrate the expected enhancement of portosystemic collaterals in the portal venous phase (Fig. 11), and scrutiny of the lesion can illustrate its connection to adjacent collateral vessels. Coronal and sagittal reformations can assist in depicting the tubular morphology of these vascular lesions. Ultrasound can help reveal the portal venous origin of these pseudo-lesions by demonstrating tubular anechoic structures on grayscale imaging with corresponding internal color flow with a monophasic waveform on color and pulsed Doppler interrogation. The presence of flow-related signal voids on MRI can also be useful in establishing the vascular nature of these findings.
Intrahepatic splenosis Splenosis is defined as autotransplantation of splenic tissue after rupture of the splenic capsule, usually from prior trauma. The splenic tissue can implant in various locations, the most common of which are the serosal surface of the small intestine and greater omentum, with intrahepatic splenosis rare [30, 31]. When the liver is involved, the splenosis is not truly intrahepatic as the splenic tissue implants on the serosal surface. On CT imaging, there is usually one or more homogenous, solid, non-calcified nodule (Fig. 13A). This entity is notorious for mimicking benign and malignant neoplastic processes. Arterial phase CT imaging can help in diagnosing splenosis as splenic tissue usually demonstrates characteristic arciform enhancement in this phase. Tc-99m-labeled heat-denatured erythrocytes or Tc-99m sulfur colloid nuclear medicine studies will show uptake in the residual splenic tissue (Fig. 13B), although the former is more specific [32]. A history of prior trauma is useful knowledge.
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Fig. 12. 66-year-old man with myelofibrosis. A Axial contrast-enhanced CT shows a retrorectal (presacral) mass (arrow). B Coronal contrast-enhanced CT shows additional masses in the upper abdomen (arrow and arrowhead). The larger mass in the right upper quadrant (arrow) contains fat
density, which can be seen with lesions containing hematopoietic elements. C Coronal CT image with bone algorithm demonstrates diffusely sclerotic osseous structures compatible with the provided history of a myeloproliferative disorder.
Fig. 13. 52-year-old woman with abdominal pain and a remote history of exploratory laparotomy. A Axial contrastenhanced CT shows a round enhancing lesion (arrow) along the posterolateral aspect of the left lobe of the liver. The
spleen is absent. B Axial image from a Tc-99m-labeled heatdenatured RBC nuclear medicine scan shows uptake in this lesion (arrow), consistent with splenic tissue.
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Conclusion Radiologists must be aware of certain entities that can mimic neoplasm on CT of the abdomen and pelvis and know how to avoid misdiagnosis, so that additional tests and potentially fatal intervention can be avoided. Acknowledgments. Christopher J. Lisanti receives royalties from Lippincott, Williams and Wilkins.
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