79
Pitfalls in Ultrasonography of Soft Tissue Tumors Esther H.Y. Hung, MBChB, FRCR, FHKAM1
James F. Griffith, MD, MRCP (UK), FRCR1
1 Department of Imaging and Interventional Radiology, Prince of
Wales Hospital, the Chinese University of Hong Kong, Hong Kong, China
Address for correspondence Esther H.Y. Hung, MBChB, FRCR, FHKAM, Department of Imaging and Interventional Radiology, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, New Territories, Hong Kong, China (e-mail: [email protected]).
Abstract
Keywords
► ► ► ►
soft tissue mass soft tissue tumor tumor pitfalls tumor ultrasonography ► ultrasonography pitfalls
Ultrasonography is increasingly the first-line investigation for the assessment of soft tissue masses. With increasing experience, most soft tissues masses, particularly superficial soft tissue masses, can be specifically labeled based on their ultrasonographic appearances. This diagnosis is based on a conundrum of clinical and ultrasonographic findings rather than resting on a single sign alone. One should try to minimize labeling the ultrasonographic appearances as “nonspecific” because this adds little to what is already known. Putting a specific label on a soft tissue mass such as a lipoma, nerve sheath tumor, or giant cell tumor of tendon sheath minimizes the need for percutaneous biopsy, greatly enhances clinical efficiency with regard to discussions on management and outcome, as well as immediately reduces patient anxiety with regard to the presence of malignancy. This article addresses the general approach to ultrasonography of soft issue masses, highlighting in particular the common pitfalls encountered in their diagnosis.
General Principles of Ultrasonography of Soft Tissue Masses The vast majority of soft tissues tumors presenting to clinical practice are benign with a malignant-to-benign ratio of 100:1. Also, most tumors are located in the subcutaneous tissues, are small to medium in size, and present as readily palpable lumps. It is often not possible to make a definitive diagnosis on the nature of the mass based on clinical grounds alone, and more importantly, it is not possible to convincingly exclude malignancy. As such, most soft tissue tumors are referred for imaging assessment soon after clinical presentation. Ultrasonography (US) is an imaging modality ideally suited to initially investigate most soft tissue lumps and bumps. It can help to (1) confirm the presence of a tumor, (2) determine its anatomical location, extent, its relationship to the investing fascia, neurovascular bundle, and other tissues, and (3) will, in most cases, allow a quite good indication as to the likely nature of the tumor. US is extremely cost effective in helping streamline the investigation of soft tissue tumors and determining which tumors can be followed up clinically,
Issue Theme Variants and Pitfalls in Musculoskeletal Imaging; Guest Editor, Wilfred C.G. Peh, MBBS, MD, FRCP (Glasg), FRCP(Edin), FRCR
which require percutaneous or excisional biopsy, and which require additional imaging investigation. Routine US-guided biopsy of all soft tissue tumors is neither practical nor cost effective, and it increases the likelihood of patient anxiety and inadvertent harm. Such a policy is not warranted given that the US appearances of most soft tissue tumors are sufficiently specific to allow one to make a definitive or near-definitive diagnosis. The US appearances of most of the common soft tissue masses are well known. These US appearances, together with the clinical picture, allow a definitive or near-definitive diagnosis in most cases to be made without the need for percutaneous biopsy or fine-needle aspiration cytology. US diagnosis of soft tissue tumors is based not just on a single imaging appearance alone but on a conundrum of clinical and imaging features (►Table 1) that provide different diagnostic weighting depending on the particular clinical context. In a recent review of > 700 superficial soft tissue tumors seen in our hospital, only 35% underwent percutaneous biopsy or surgical excision, yet clinical follow-up showed that no malignant lesion was misdiagnosed over that time period.1
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1365837. ISSN 1089-7860.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Semin Musculoskelet Radiol 2014;18:79–85.
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
Table 1 Main clinical and ultrasonographic factors to consider during ultrasonography of a soft tissue mass Clinical How long has the mass been present? Is the mass growing, static in size, or becoming smaller? Is the mass painful or tender? Is there more than one mass? Has there been an injury to this area? Is there a known malignancy? Ultrasonography Location: Central or peripheral body location. Dermal, subcutaneous, fascial, subfascial, intermuscular, intramuscular, submuscular, juxtacortical, periosteal, arising from joint, subungual Appearances: Size, shape, well defined or ill defined, encapsulation, internal echogenicity, internal architecture (linear echoes, speckles, comet pain artifacts, calcification, cystic areas, acoustic transmission) Consistency: Compressible soft, firm, hard Color Doppler imaging: Presence or absence of hyperemia, level of hyperemia, peripheral or central pattern or mixed, organized, or chaotic vascular pattern Surrounding soft tissues: Relationship to tendon, tendon sheath, nerves, joints, fascia Edema, swelling, and hyperemia of surrounding soft tissues
One of the golden caveats to follow when performing US of musculoskeletal tumors is not to label a tumor as benign unless one can put a specific label on that tumor based on the US appearance. In other words, one can correctly label a tumor as benign if one can say, based on the clinical and US appearance, that it is, for example, a nerve sheath tumor, lipoma, fibromatosis, or giant cell tumor of tendon sheath. Similarly, for tumors that have been present for a long time (more than a year) without a change in size, one can happily label them benign provided no aggressive features are present such as infiltration on US examination, and thus it is reasonable to continue following up these tumors clinically without histologic confirmation. For all other soft tissues tumors, with a short history (less than a year), one should not label the tumor as benign if the appearance on US is nonspecific. A large size at presentation, rapid growth, deep location, and hyperemic chaotic-type vasculature on color Doppler imaging are all more common in malignant tumors. However, malignant tumors may be small at presentation, may be located in the superficial tissues, and may not necessarily have demonstrable flow on color Doppler imaging. Similarly, it is well recognized that occasionally malignant tumors can have a protracted clinical course, whereas benign tumors can present over a relatively short time span. In addition to the criteria already mentioned, one of the most important for the diagnosis of malignant tumors is that the tumor does not Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
conform to the recognized US appearance of a benign tumor. In other words, when the tumor does not look like any recognized tumor, and, particularly if it has additional suspicious features (large size, rapid growth, deep location, chaotic-type hyperemia), this should prompt one to consider a malignant tumor. One needs to be aware of the level of certainty with which specific diagnoses can be made based on the US appearance. Subsequent management depends very much on the label applied to a tumor. Being able to label tumors specifically tumors based on their imaging appearances alone greatly enhances clinical efficacy and also helps alleviate patient anxiety. A large number of the patients who present with a soft tissue lump are concerned about the possibility of malignancy. Immediate reassurance at the time of US examination greatly alleviates this anxiety. Such reassurance, however, can only be provided if the attending radiologist is able to make a specific diagnosis based on US appearances alone. The radiologist should be familiar with the specific tumor types that can be diagnosed with a quite high level of certainty with US and recognize that even with these tumors, pitfalls may occasionally arise when these tumors present with atypical US appearances. Following US examination, one should undertake percutaneous biopsy or recommend excisional biopsy only for those selected tumors in which one is unsure of the diagnosis and has a moderate to high index of suspicion of malignancy. For those tumors, in which one is unsure and has a low index of suspicion, one can either follow up with repeat imaging or proceed to additional imaging. The remainder of this article focuses on nontumoral conditions that may mimic tumors on US and US appearances of some common tumors that can mimic those of other common tumors.
Fig. 1 Intramuscular hematoma. A 25-year-old man presented with a sudden onset of right anterior thigh swelling 2 weeks after playing football although with no specific history of injury. Longitudinal grayscale ultrasound image shows a well-defined solid appearing mass (arrows) within the vastus interomedialis muscle. No hyperemia was present. The appearances are consistent with an intramuscular hematoma that gradually resolved on serial follow-up.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
80
Hung, Griffith
Fig. 2 Organizing hematoma. A 65-year-old woman presented with an enlarging buttock mass. (a) Longitudinal gray-scale ultrasound (US) image shows a large well-defined soft tissue mass overlying the coccyx (arrows). (b) Longitudinal color Doppler US image shows the presence of intralesional vascularity. Percutaneous biopsy confirmed an organized hematoma.
Nontumoral Conditions That May Mimic Tumors on Ultrasonography Hematoma The diagnosis of hematoma is straightforward when there is a clear history of trauma. However, in many instances, this history is not available. Hematoma can occur from blood vessel rupture during physical exertion, especially in patients with a coagulation disorder, on anticoagulant therapy, or taking aspirin prophylactically. In these situations, patients usually present several weeks or months following the episode of bleeding when the hemorrhage begins to organize with fibroblastic proliferation and endothelial cell ingrowth into the periphery of the clot with removal of necrotic cellular elements by phagocytosis and reabsorption of serous elements. This leads to the clot becoming harder and clinically palpable, prompting referral for imaging. The typical US appearance of a hematoma at this stage is a quite welldefined mass, hyperechoic to adjacent muscle, often with a multilaminated whorled appearance, small areas of liquefac-
tion, and marginal hyperemic (►Fig. 1). One can usually make the diagnosis on US. If necessary, T2-weighted gradient-echo MR imaging can help confirm the presence of hemosiderin.
Organizing Hematoma and Thrombi Organizing hematoma and thrombi develop when a fibrous capsule forms around the hematoma that limits sufficient vascular ingrowth and hence absorption. If further bleeding occurs, the hematoma expands and simulates a growing soft tissue tumor such as a nerve sheath tumor, epidermoid cyst, or sarcoma. Both peripheral and central vascularity may be seen on color Doppler imaging (►Fig. 2a, b, ►Fig. 3a, b). A history of trauma is not usually present, although these lesions do tend to occur near bony prominences, presumably increasing the likelihood of repeated minor trauma and repeated hemorrhage. Distinguishing features from other tumors are few. One needs to be aware of this diagnosis and consider it as a differential in certain soft tissue masses. Percutaneous biopsy is usually
Fig. 3 Organizing hematoma. (a) Clinical photograph of a 68-year-old man with an enlarging mass (arrows) over the right iliac crest region for the past 2 months. (b) Gray-scale ultrasound (US) image shows that the mass is mildly echogenic with several intrinsic whorl-like patterns (arrows) consistent with an organizing hematoma. Color Doppler US image (not shown) revealed no intrinsic hyperemia. US-guided percutaneous biopsy was performed that confirmed an organizing hematoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
81
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Pitfalls in Ultrasonography of Soft Tissue Tumors
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
Fig. 4 Muscle tear. A 65-year-old woman with recent onset of painful medial thigh swelling. There was no history of trauma. (a) Coronal T2-weighted MR image shows a medium-size ill-defined hyperintense mass within the gracilis muscle (arrow). (b) Contrast-enhanced axial fatsuppressed T1-weighted MR image shows the gracilis lesion to be hyperemic with marked contrast enhancement (arrow). (c) Axial positron emission tomography-computed tomography (PET-CT) image shows the lesion (arrow) to be hypermetabolic with a standardized uptake value of 4.4. These MR imaging and PET-CT appearances were suspicious for a malignant tumor, and the patient was referred for ultrasound (US)-guided biopsy. (d) Transverse gray-scale US image shows a mild ill-defined swelling of the gracilis muscle with preservation of the internal muscular fibrillary echotexture (arrows). Because these appearances were not consistent with a muscle tumor, no biopsy was undertaken. (e) Follow-up transverse gray-scale US image 1 month later shows near-complete resolution of the gracilis muscle lesion and associated mild muscle atrophy. Overall appearances are compatible with a healed muscle tear.
necessary in this particular context. Organizing thrombus is similar to organizing hematoma except that it occurs within vessel thrombi with ingrowth of endothelial cells, smooth muscle, and fibroblasts to form a fibrin-rich thrombus. Both organizing hematoma and organizing thrombi can revascularize and thus resemble tumor masses. 2 Organizing thrombus is usually not that problematic because it occurs within a vessel and is much smaller than organizing hematoma.
Anomalous Muscles Although common in the musculoskeletal system, anomalous muscles hardly ever cause difficulty with regard to simulating sarcoma because they show the typical
Muscle Tear Muscle tears can occasionally occur in the absence of any specific injury. Reparative healing of such tears can simulate soft tissue sarcomas.3 These lesions appear on US as irregular hyperechoic masses with marginal hyperemia and edema. Usually, no discrete tear is present. As always, being aware of this entity and correlating the clinical history and serial progress together with the US findings helps one to make this diagnosis. US is particularly helpful because it usually allows one to appreciate the underlying, albeit altered, muscle echotexture more readily than on other imaging modalities and has the dynamic component where one can see the muscle tear pseudotear move with muscle contraction. Additional imaging such as positron emission tomography imaging may add to the confusion because these lesions often show increased metabolic activity due to ongoing muscle repair and thus may simulate malignant tumors (►Fig. 4a–d). Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
Fig. 5 Diabetic muscle infarction. A 35-year-old man with diabetic nephropathy presented with gradual onset of thigh swelling over a few days. Transverse gray-scale ultrasound image shows an ill-defined localized swelling within the vastus interomedialis and vastus medialis muscles. Moderate peripheral hyperemia was demonstrated on color Doppler imaging (not shown). In this clinical context, the appearances are consistent with diabetic muscle infarction. The lesion gradually resolved over the ensuing 2 months.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
82
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
83
US Appearances of Some Common Tumors Mimicking Other Tumors The US accuracy of making the diagnosis of slow-flow vascular malformation is high when the typical appearances of a lipomatous mass with large dilated vascular channels, phleboliths, and slow intravascular flow are more readily visible on real-time gray-scale US rather than color Doppler imaging. In our experience, for superficial soft tissue tumors, the sensitivity and specificity of US in making a firm diagnosis of a vascular malformation is 73% and 98%, respectibely.1 Most errors occur when the vascular malformations are of very slow flow, and if the lesion is composed of mainly echogenic stroma interspersed with small capillaries that are too small to be resolved by US. These lesions are sometimes misdiagnosed as lipoma ( ►Fig. 6a, b).
Atypical Lipoma In general, the accuracy of US in making a diagnosis of lipoma is high. This high level of accuracy applies particularly to superficial lipoma but also subfascial lipoma to a lesser degree. In our experience, the accuracy of US in diagnosing superficial lipoma has a sensitivity and specificity of 95% and 94%, respectively.1 A small number of lipomas are more hypoechoic than usual without the typical thin linear Fig. 6 Slow-flow vascular anomaly. A 48-year-old woman presented with a long-standing ankle mass that had increased in size recently. (a) Longitudinal gray-scale ultrasound (US) image shows a well-defined lobulated lipomatous appearing mass (arrow) on the medial aspect of the ankle joint. (b) Longitudinal color Doppler US image shows no detectable intralesional vascularity. The ultrasonographic appearances were initially considered to be a fibrolipoma with a differential diagnosis of a chronic epidermoid cyst. The lesion was later proven pathologically to be a vascular malformation.
unmistakable US (or MR imaging) appearances and shape of skeletal muscle.
Diabetic Muscle Infarction Diabetic muscle infarction typically gives rise to a focal illdefined swelling and hypoechogenicity within muscle that may be misinterpreted as a sarcoma or muscle metastatic deposit. One may see surrounding muscle or subcutaneous edema. Intralesional hemorrhage, fluid collection, or gas may occur. Initially, the affected area is hypovascular relative to the surrounding muscle but later become hyperemic.4 The typical patient has poorly controlled diabetes mellitus with nephropathy, neuropathy, or retinopathy that presents with an acute onset of muscle pain and swelling. This mainly subsides after about a week, at which stage a clinically palpable muscle mass may be present, simulating a sarcoma (►Fig. 5). Serial US examinations can help confirm the diagnosis, with progressive peripheral hyperemia, delineation, and regression of the infarction muscle area seen on serial US examinations.
Fig. 7 Atypical lipoma. A 51-year-old woman presented with a painless enlarging nodule in her right middle finger. (a) Transverse and (b) longitudinal gray-scale ultrasound images show a well-encapsulated relatively hypoechoic subcutaneous nodule (black arrows) with a few internal linear hyperechoic strands (white arrows) and small hypoechoic areas (curved arrows). The lesion was initially diagnosed as an epidermoid cyst but was later proven pathologically to be a lipoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Lipoma versus Slow-Flow Vascular Malformation
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
striations running parallel to the skin surface. In retrospect, even for these tumors, the US appearances of lipoma are still usually present, although they are more subtle than one usually encounters. These more atypical superficial lipomas are not infrequently misdiagnosed as epidermoid cysts (►Fig. 7a, b).
Nerve Sheath Tumor versus Vascular Leiomyoma Both nerve sheath tumors and vascular leiomyomas occur adjacent to the neurovascular bundle and are therefore open to misinterpretation. The typical US appearances of neural thickening of the entering and exiting nerves are not invariably evident in nerve sheath tumors arising from small peripheral nerves. In this instance, the US description of a small well-defined hypoechoic mass with internal hypoechoic areas and moderate hyperemia could well apply to either a nerve sheath tumor or a vascular leiomyoma (►Fig. 8a, b). Both these lesions occur alongside the neurovascular bundle, further adding to the confusion. The main distinguishing feature recognized thus far is that angioleiomyomas tend to have linear vessels with convergence to one point on color Doppler imaging.5
Atypical Nerve Sheath Tumors A small percentage of nerve tumors can either show no internal vascularity on color Doppler imaging or else possess
Fig. 9 Degenerated schwannoma. A 67-year-old man with lateral calf swelling and foot drop. (a) Transverse gray-scale ultrasound (US) image shows a predominantly cystic mass (arrows) present within the peroneus longus muscle. (b) Transverse color Doppler US image shows mild vascularity (arrows) along the wall of the cystic mass, but there is no central vascularity. This lesion, which is a cystic or degenerated schwannoma, may mimic a ganglion cyst or myxoma.
a purely cystic component as in a so-called ancient schwannoma. Both of these tumor types are clearly open to misinterpretation. Nerve sheath tumor without apparent vascularity may be misdiagnosed as a fibroma or granuloma on US. Alternatively, purely or partially cystic nerve sheath tumors may be diagnosed as ganglia or myxoma (►Fig. 9a, b). The clue in both these instances to the presence of a nerve sheath tumor would be demonstrable continuity with a parent nerve.
Conclusion
Fig. 8 Vascular leiomyoma. A 31-year-old woman with a painful calf nodule. (a) Longitudinal gray-scale ultrasound (US) image shows a welldefined solid hypoechoic subcutaneous mass (arrows). (b) Color Doppler US image shows linear intralesional vessels that converge to one point eccentrically (arrow). The lesion was initially diagnosed as a nerve sheath tumor but was later proven histologically to be a vascular leiomyoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
As radiologists become more familiar with the varied appearances of soft tissue masses, US is becoming more accurate at arriving at a specific diagnosis of soft tissue masses, particularly superficial soft tissue masses, based on the US appearance alone. This helps optimize clinical efficiency and reduce patient anxiety. Also, being aware of the common and varied appearances of soft tissue tumors on US allows one to isolate with greater clarity
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
84
Pitfalls in Ultrasonography of Soft Tissue Tumors
References 1 Hung EHY, Griffith JF, Ng AWH, Lee RKL, Lau DTY, Leung JCS.
Ultrasound of musculoskeletal soft tissue tumors superficial to the investing fascia. AJR Am J Roentgenol. In press
85
2 Ryu JK, Jin W, Kim GY. Sonographic appearances of small organiz-
ing hematomas and thrombi mimicking superficial soft tissue tumors. J Ultrasound Med 2011;30(10):1431–1436 3 Walker E, Brian P, Longo V, Fox EJ, Frauenhoffer EE, Murphey M. Dilemmas in distinguishing between tumor and the posttraumatic lesion with surgical or pathologic correlation. Clin Sports Med 2013;32(3):559–576 4 Baker JC, Demertzis JL, Rhodes NG, Wessell DE, Rubin DA. Diabetic musculoskeletal complications and their imaging mimics. Radiographics 2012;32(7):1959–1974 5 Park HJ, Kim SS, Lee SY, Choi YJ, Chung EC, Rho MH. Sonographic appearances of soft tissue angioleiomyomas: differences from other circumscribed soft tissue hypervascular tumors. J Ultrasound Med 2012;31(10):1589–1595
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
the likelihood of a more sinister lesion that does not fit into recognizable tumor patterns and warrants further investigation, biopsy, or imaging follow-up. In this article, we presented some of the common mimics that one may encounter during routine US practice.
Hung, Griffith
Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
Copyright of Seminars in Musculoskeletal Radiology is the property of Thieme Medical Publishing Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Pitfalls in Ultrasonography of Soft Tissue Tumors Esther H.Y. Hung, MBChB, FRCR, FHKAM1
James F. Griffith, MD, MRCP (UK), FRCR1
1 Department of Imaging and Interventional Radiology, Prince of
Wales Hospital, the Chinese University of Hong Kong, Hong Kong, China
Address for correspondence Esther H.Y. Hung, MBChB, FRCR, FHKAM, Department of Imaging and Interventional Radiology, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, New Territories, Hong Kong, China (e-mail: [email protected]).
Abstract
Keywords
► ► ► ►
soft tissue mass soft tissue tumor tumor pitfalls tumor ultrasonography ► ultrasonography pitfalls
Ultrasonography is increasingly the first-line investigation for the assessment of soft tissue masses. With increasing experience, most soft tissues masses, particularly superficial soft tissue masses, can be specifically labeled based on their ultrasonographic appearances. This diagnosis is based on a conundrum of clinical and ultrasonographic findings rather than resting on a single sign alone. One should try to minimize labeling the ultrasonographic appearances as “nonspecific” because this adds little to what is already known. Putting a specific label on a soft tissue mass such as a lipoma, nerve sheath tumor, or giant cell tumor of tendon sheath minimizes the need for percutaneous biopsy, greatly enhances clinical efficiency with regard to discussions on management and outcome, as well as immediately reduces patient anxiety with regard to the presence of malignancy. This article addresses the general approach to ultrasonography of soft issue masses, highlighting in particular the common pitfalls encountered in their diagnosis.
General Principles of Ultrasonography of Soft Tissue Masses The vast majority of soft tissues tumors presenting to clinical practice are benign with a malignant-to-benign ratio of 100:1. Also, most tumors are located in the subcutaneous tissues, are small to medium in size, and present as readily palpable lumps. It is often not possible to make a definitive diagnosis on the nature of the mass based on clinical grounds alone, and more importantly, it is not possible to convincingly exclude malignancy. As such, most soft tissue tumors are referred for imaging assessment soon after clinical presentation. Ultrasonography (US) is an imaging modality ideally suited to initially investigate most soft tissue lumps and bumps. It can help to (1) confirm the presence of a tumor, (2) determine its anatomical location, extent, its relationship to the investing fascia, neurovascular bundle, and other tissues, and (3) will, in most cases, allow a quite good indication as to the likely nature of the tumor. US is extremely cost effective in helping streamline the investigation of soft tissue tumors and determining which tumors can be followed up clinically,
Issue Theme Variants and Pitfalls in Musculoskeletal Imaging; Guest Editor, Wilfred C.G. Peh, MBBS, MD, FRCP (Glasg), FRCP(Edin), FRCR
which require percutaneous or excisional biopsy, and which require additional imaging investigation. Routine US-guided biopsy of all soft tissue tumors is neither practical nor cost effective, and it increases the likelihood of patient anxiety and inadvertent harm. Such a policy is not warranted given that the US appearances of most soft tissue tumors are sufficiently specific to allow one to make a definitive or near-definitive diagnosis. The US appearances of most of the common soft tissue masses are well known. These US appearances, together with the clinical picture, allow a definitive or near-definitive diagnosis in most cases to be made without the need for percutaneous biopsy or fine-needle aspiration cytology. US diagnosis of soft tissue tumors is based not just on a single imaging appearance alone but on a conundrum of clinical and imaging features (►Table 1) that provide different diagnostic weighting depending on the particular clinical context. In a recent review of > 700 superficial soft tissue tumors seen in our hospital, only 35% underwent percutaneous biopsy or surgical excision, yet clinical follow-up showed that no malignant lesion was misdiagnosed over that time period.1
Copyright © 2014 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.
DOI http://dx.doi.org/ 10.1055/s-0034-1365837. ISSN 1089-7860.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Semin Musculoskelet Radiol 2014;18:79–85.
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
Table 1 Main clinical and ultrasonographic factors to consider during ultrasonography of a soft tissue mass Clinical How long has the mass been present? Is the mass growing, static in size, or becoming smaller? Is the mass painful or tender? Is there more than one mass? Has there been an injury to this area? Is there a known malignancy? Ultrasonography Location: Central or peripheral body location. Dermal, subcutaneous, fascial, subfascial, intermuscular, intramuscular, submuscular, juxtacortical, periosteal, arising from joint, subungual Appearances: Size, shape, well defined or ill defined, encapsulation, internal echogenicity, internal architecture (linear echoes, speckles, comet pain artifacts, calcification, cystic areas, acoustic transmission) Consistency: Compressible soft, firm, hard Color Doppler imaging: Presence or absence of hyperemia, level of hyperemia, peripheral or central pattern or mixed, organized, or chaotic vascular pattern Surrounding soft tissues: Relationship to tendon, tendon sheath, nerves, joints, fascia Edema, swelling, and hyperemia of surrounding soft tissues
One of the golden caveats to follow when performing US of musculoskeletal tumors is not to label a tumor as benign unless one can put a specific label on that tumor based on the US appearance. In other words, one can correctly label a tumor as benign if one can say, based on the clinical and US appearance, that it is, for example, a nerve sheath tumor, lipoma, fibromatosis, or giant cell tumor of tendon sheath. Similarly, for tumors that have been present for a long time (more than a year) without a change in size, one can happily label them benign provided no aggressive features are present such as infiltration on US examination, and thus it is reasonable to continue following up these tumors clinically without histologic confirmation. For all other soft tissues tumors, with a short history (less than a year), one should not label the tumor as benign if the appearance on US is nonspecific. A large size at presentation, rapid growth, deep location, and hyperemic chaotic-type vasculature on color Doppler imaging are all more common in malignant tumors. However, malignant tumors may be small at presentation, may be located in the superficial tissues, and may not necessarily have demonstrable flow on color Doppler imaging. Similarly, it is well recognized that occasionally malignant tumors can have a protracted clinical course, whereas benign tumors can present over a relatively short time span. In addition to the criteria already mentioned, one of the most important for the diagnosis of malignant tumors is that the tumor does not Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
conform to the recognized US appearance of a benign tumor. In other words, when the tumor does not look like any recognized tumor, and, particularly if it has additional suspicious features (large size, rapid growth, deep location, chaotic-type hyperemia), this should prompt one to consider a malignant tumor. One needs to be aware of the level of certainty with which specific diagnoses can be made based on the US appearance. Subsequent management depends very much on the label applied to a tumor. Being able to label tumors specifically tumors based on their imaging appearances alone greatly enhances clinical efficacy and also helps alleviate patient anxiety. A large number of the patients who present with a soft tissue lump are concerned about the possibility of malignancy. Immediate reassurance at the time of US examination greatly alleviates this anxiety. Such reassurance, however, can only be provided if the attending radiologist is able to make a specific diagnosis based on US appearances alone. The radiologist should be familiar with the specific tumor types that can be diagnosed with a quite high level of certainty with US and recognize that even with these tumors, pitfalls may occasionally arise when these tumors present with atypical US appearances. Following US examination, one should undertake percutaneous biopsy or recommend excisional biopsy only for those selected tumors in which one is unsure of the diagnosis and has a moderate to high index of suspicion of malignancy. For those tumors, in which one is unsure and has a low index of suspicion, one can either follow up with repeat imaging or proceed to additional imaging. The remainder of this article focuses on nontumoral conditions that may mimic tumors on US and US appearances of some common tumors that can mimic those of other common tumors.
Fig. 1 Intramuscular hematoma. A 25-year-old man presented with a sudden onset of right anterior thigh swelling 2 weeks after playing football although with no specific history of injury. Longitudinal grayscale ultrasound image shows a well-defined solid appearing mass (arrows) within the vastus interomedialis muscle. No hyperemia was present. The appearances are consistent with an intramuscular hematoma that gradually resolved on serial follow-up.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
80
Hung, Griffith
Fig. 2 Organizing hematoma. A 65-year-old woman presented with an enlarging buttock mass. (a) Longitudinal gray-scale ultrasound (US) image shows a large well-defined soft tissue mass overlying the coccyx (arrows). (b) Longitudinal color Doppler US image shows the presence of intralesional vascularity. Percutaneous biopsy confirmed an organized hematoma.
Nontumoral Conditions That May Mimic Tumors on Ultrasonography Hematoma The diagnosis of hematoma is straightforward when there is a clear history of trauma. However, in many instances, this history is not available. Hematoma can occur from blood vessel rupture during physical exertion, especially in patients with a coagulation disorder, on anticoagulant therapy, or taking aspirin prophylactically. In these situations, patients usually present several weeks or months following the episode of bleeding when the hemorrhage begins to organize with fibroblastic proliferation and endothelial cell ingrowth into the periphery of the clot with removal of necrotic cellular elements by phagocytosis and reabsorption of serous elements. This leads to the clot becoming harder and clinically palpable, prompting referral for imaging. The typical US appearance of a hematoma at this stage is a quite welldefined mass, hyperechoic to adjacent muscle, often with a multilaminated whorled appearance, small areas of liquefac-
tion, and marginal hyperemic (►Fig. 1). One can usually make the diagnosis on US. If necessary, T2-weighted gradient-echo MR imaging can help confirm the presence of hemosiderin.
Organizing Hematoma and Thrombi Organizing hematoma and thrombi develop when a fibrous capsule forms around the hematoma that limits sufficient vascular ingrowth and hence absorption. If further bleeding occurs, the hematoma expands and simulates a growing soft tissue tumor such as a nerve sheath tumor, epidermoid cyst, or sarcoma. Both peripheral and central vascularity may be seen on color Doppler imaging (►Fig. 2a, b, ►Fig. 3a, b). A history of trauma is not usually present, although these lesions do tend to occur near bony prominences, presumably increasing the likelihood of repeated minor trauma and repeated hemorrhage. Distinguishing features from other tumors are few. One needs to be aware of this diagnosis and consider it as a differential in certain soft tissue masses. Percutaneous biopsy is usually
Fig. 3 Organizing hematoma. (a) Clinical photograph of a 68-year-old man with an enlarging mass (arrows) over the right iliac crest region for the past 2 months. (b) Gray-scale ultrasound (US) image shows that the mass is mildly echogenic with several intrinsic whorl-like patterns (arrows) consistent with an organizing hematoma. Color Doppler US image (not shown) revealed no intrinsic hyperemia. US-guided percutaneous biopsy was performed that confirmed an organizing hematoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
81
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Pitfalls in Ultrasonography of Soft Tissue Tumors
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
Fig. 4 Muscle tear. A 65-year-old woman with recent onset of painful medial thigh swelling. There was no history of trauma. (a) Coronal T2-weighted MR image shows a medium-size ill-defined hyperintense mass within the gracilis muscle (arrow). (b) Contrast-enhanced axial fatsuppressed T1-weighted MR image shows the gracilis lesion to be hyperemic with marked contrast enhancement (arrow). (c) Axial positron emission tomography-computed tomography (PET-CT) image shows the lesion (arrow) to be hypermetabolic with a standardized uptake value of 4.4. These MR imaging and PET-CT appearances were suspicious for a malignant tumor, and the patient was referred for ultrasound (US)-guided biopsy. (d) Transverse gray-scale US image shows a mild ill-defined swelling of the gracilis muscle with preservation of the internal muscular fibrillary echotexture (arrows). Because these appearances were not consistent with a muscle tumor, no biopsy was undertaken. (e) Follow-up transverse gray-scale US image 1 month later shows near-complete resolution of the gracilis muscle lesion and associated mild muscle atrophy. Overall appearances are compatible with a healed muscle tear.
necessary in this particular context. Organizing thrombus is similar to organizing hematoma except that it occurs within vessel thrombi with ingrowth of endothelial cells, smooth muscle, and fibroblasts to form a fibrin-rich thrombus. Both organizing hematoma and organizing thrombi can revascularize and thus resemble tumor masses. 2 Organizing thrombus is usually not that problematic because it occurs within a vessel and is much smaller than organizing hematoma.
Anomalous Muscles Although common in the musculoskeletal system, anomalous muscles hardly ever cause difficulty with regard to simulating sarcoma because they show the typical
Muscle Tear Muscle tears can occasionally occur in the absence of any specific injury. Reparative healing of such tears can simulate soft tissue sarcomas.3 These lesions appear on US as irregular hyperechoic masses with marginal hyperemia and edema. Usually, no discrete tear is present. As always, being aware of this entity and correlating the clinical history and serial progress together with the US findings helps one to make this diagnosis. US is particularly helpful because it usually allows one to appreciate the underlying, albeit altered, muscle echotexture more readily than on other imaging modalities and has the dynamic component where one can see the muscle tear pseudotear move with muscle contraction. Additional imaging such as positron emission tomography imaging may add to the confusion because these lesions often show increased metabolic activity due to ongoing muscle repair and thus may simulate malignant tumors (►Fig. 4a–d). Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
Fig. 5 Diabetic muscle infarction. A 35-year-old man with diabetic nephropathy presented with gradual onset of thigh swelling over a few days. Transverse gray-scale ultrasound image shows an ill-defined localized swelling within the vastus interomedialis and vastus medialis muscles. Moderate peripheral hyperemia was demonstrated on color Doppler imaging (not shown). In this clinical context, the appearances are consistent with diabetic muscle infarction. The lesion gradually resolved over the ensuing 2 months.
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
82
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
83
US Appearances of Some Common Tumors Mimicking Other Tumors The US accuracy of making the diagnosis of slow-flow vascular malformation is high when the typical appearances of a lipomatous mass with large dilated vascular channels, phleboliths, and slow intravascular flow are more readily visible on real-time gray-scale US rather than color Doppler imaging. In our experience, for superficial soft tissue tumors, the sensitivity and specificity of US in making a firm diagnosis of a vascular malformation is 73% and 98%, respectibely.1 Most errors occur when the vascular malformations are of very slow flow, and if the lesion is composed of mainly echogenic stroma interspersed with small capillaries that are too small to be resolved by US. These lesions are sometimes misdiagnosed as lipoma ( ►Fig. 6a, b).
Atypical Lipoma In general, the accuracy of US in making a diagnosis of lipoma is high. This high level of accuracy applies particularly to superficial lipoma but also subfascial lipoma to a lesser degree. In our experience, the accuracy of US in diagnosing superficial lipoma has a sensitivity and specificity of 95% and 94%, respectively.1 A small number of lipomas are more hypoechoic than usual without the typical thin linear Fig. 6 Slow-flow vascular anomaly. A 48-year-old woman presented with a long-standing ankle mass that had increased in size recently. (a) Longitudinal gray-scale ultrasound (US) image shows a well-defined lobulated lipomatous appearing mass (arrow) on the medial aspect of the ankle joint. (b) Longitudinal color Doppler US image shows no detectable intralesional vascularity. The ultrasonographic appearances were initially considered to be a fibrolipoma with a differential diagnosis of a chronic epidermoid cyst. The lesion was later proven pathologically to be a vascular malformation.
unmistakable US (or MR imaging) appearances and shape of skeletal muscle.
Diabetic Muscle Infarction Diabetic muscle infarction typically gives rise to a focal illdefined swelling and hypoechogenicity within muscle that may be misinterpreted as a sarcoma or muscle metastatic deposit. One may see surrounding muscle or subcutaneous edema. Intralesional hemorrhage, fluid collection, or gas may occur. Initially, the affected area is hypovascular relative to the surrounding muscle but later become hyperemic.4 The typical patient has poorly controlled diabetes mellitus with nephropathy, neuropathy, or retinopathy that presents with an acute onset of muscle pain and swelling. This mainly subsides after about a week, at which stage a clinically palpable muscle mass may be present, simulating a sarcoma (►Fig. 5). Serial US examinations can help confirm the diagnosis, with progressive peripheral hyperemia, delineation, and regression of the infarction muscle area seen on serial US examinations.
Fig. 7 Atypical lipoma. A 51-year-old woman presented with a painless enlarging nodule in her right middle finger. (a) Transverse and (b) longitudinal gray-scale ultrasound images show a well-encapsulated relatively hypoechoic subcutaneous nodule (black arrows) with a few internal linear hyperechoic strands (white arrows) and small hypoechoic areas (curved arrows). The lesion was initially diagnosed as an epidermoid cyst but was later proven pathologically to be a lipoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Lipoma versus Slow-Flow Vascular Malformation
Pitfalls in Ultrasonography of Soft Tissue Tumors
Hung, Griffith
striations running parallel to the skin surface. In retrospect, even for these tumors, the US appearances of lipoma are still usually present, although they are more subtle than one usually encounters. These more atypical superficial lipomas are not infrequently misdiagnosed as epidermoid cysts (►Fig. 7a, b).
Nerve Sheath Tumor versus Vascular Leiomyoma Both nerve sheath tumors and vascular leiomyomas occur adjacent to the neurovascular bundle and are therefore open to misinterpretation. The typical US appearances of neural thickening of the entering and exiting nerves are not invariably evident in nerve sheath tumors arising from small peripheral nerves. In this instance, the US description of a small well-defined hypoechoic mass with internal hypoechoic areas and moderate hyperemia could well apply to either a nerve sheath tumor or a vascular leiomyoma (►Fig. 8a, b). Both these lesions occur alongside the neurovascular bundle, further adding to the confusion. The main distinguishing feature recognized thus far is that angioleiomyomas tend to have linear vessels with convergence to one point on color Doppler imaging.5
Atypical Nerve Sheath Tumors A small percentage of nerve tumors can either show no internal vascularity on color Doppler imaging or else possess
Fig. 9 Degenerated schwannoma. A 67-year-old man with lateral calf swelling and foot drop. (a) Transverse gray-scale ultrasound (US) image shows a predominantly cystic mass (arrows) present within the peroneus longus muscle. (b) Transverse color Doppler US image shows mild vascularity (arrows) along the wall of the cystic mass, but there is no central vascularity. This lesion, which is a cystic or degenerated schwannoma, may mimic a ganglion cyst or myxoma.
a purely cystic component as in a so-called ancient schwannoma. Both of these tumor types are clearly open to misinterpretation. Nerve sheath tumor without apparent vascularity may be misdiagnosed as a fibroma or granuloma on US. Alternatively, purely or partially cystic nerve sheath tumors may be diagnosed as ganglia or myxoma (►Fig. 9a, b). The clue in both these instances to the presence of a nerve sheath tumor would be demonstrable continuity with a parent nerve.
Conclusion
Fig. 8 Vascular leiomyoma. A 31-year-old woman with a painful calf nodule. (a) Longitudinal gray-scale ultrasound (US) image shows a welldefined solid hypoechoic subcutaneous mass (arrows). (b) Color Doppler US image shows linear intralesional vessels that converge to one point eccentrically (arrow). The lesion was initially diagnosed as a nerve sheath tumor but was later proven histologically to be a vascular leiomyoma. Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
As radiologists become more familiar with the varied appearances of soft tissue masses, US is becoming more accurate at arriving at a specific diagnosis of soft tissue masses, particularly superficial soft tissue masses, based on the US appearance alone. This helps optimize clinical efficiency and reduce patient anxiety. Also, being aware of the common and varied appearances of soft tissue tumors on US allows one to isolate with greater clarity
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
84
Pitfalls in Ultrasonography of Soft Tissue Tumors
References 1 Hung EHY, Griffith JF, Ng AWH, Lee RKL, Lau DTY, Leung JCS.
Ultrasound of musculoskeletal soft tissue tumors superficial to the investing fascia. AJR Am J Roentgenol. In press
85
2 Ryu JK, Jin W, Kim GY. Sonographic appearances of small organiz-
ing hematomas and thrombi mimicking superficial soft tissue tumors. J Ultrasound Med 2011;30(10):1431–1436 3 Walker E, Brian P, Longo V, Fox EJ, Frauenhoffer EE, Murphey M. Dilemmas in distinguishing between tumor and the posttraumatic lesion with surgical or pathologic correlation. Clin Sports Med 2013;32(3):559–576 4 Baker JC, Demertzis JL, Rhodes NG, Wessell DE, Rubin DA. Diabetic musculoskeletal complications and their imaging mimics. Radiographics 2012;32(7):1959–1974 5 Park HJ, Kim SS, Lee SY, Choi YJ, Chung EC, Rho MH. Sonographic appearances of soft tissue angioleiomyomas: differences from other circumscribed soft tissue hypervascular tumors. J Ultrasound Med 2012;31(10):1589–1595
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
the likelihood of a more sinister lesion that does not fit into recognizable tumor patterns and warrants further investigation, biopsy, or imaging follow-up. In this article, we presented some of the common mimics that one may encounter during routine US practice.
Hung, Griffith
Seminars in Musculoskeletal Radiology
Vol. 18
No. 1/2014
Copyright of Seminars in Musculoskeletal Radiology is the property of Thieme Medical Publishing Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
