Pediatr Radiol (2015) 45:118–123 DOI 10.1007/s00247-014-3188-5
Blunt renal trauma in children with pre-existing renal abnormalities Kelly Dahlstrom & Brian Dunoski & Jeffrey Michael Zerin
Received: 1 May 2014 / Revised: 25 July 2014 / Accepted: 11 September 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract The kidneys are the most commonly injured genitourinary organ in children following blunt abdominal trauma. Though the retroperitoneal location affords the kidneys some protection from the forces experienced in blunt abdominal trauma, the kidneys are at greater risk of injury when a disease process exposes them from their normal shielded location. In such cases, the injuries may appear to be disproportionate in relation to the severity of the trauma history, confusing the imaging findings. Recognition of both the underlying disease process as well as the manifestations of acute trauma is important; therefore, we present a pictorial essay of traumatized kidneys in children with pre-existing renal abnormalities. Keywords Renal trauma . Kidney . Computed tomography . Genitourinary tract . Renal tumor . Congenital anomaly . Children
Introduction The kidney is the most common genitourinary tract organ to sustain injury following blunt abdominal trauma in children, CME activity This article has been selected as the CME activity for the current month. Please visit the SPR Web site at www.pedrad.org on the Education page and follow the instructions to complete this CME activity. K. Dahlstrom Kansas City University of Medicine and Biosciences, Kansas City, MO, USA B. Dunoski (*) Pediatric Radiology Department, Children’s Mercy Hospital and Clinics, 2401 Gillham Road, Kansas City, MO 64108, USA e-mail: [email protected]
J. M. Zerin Division of Pediatric Imaging, Children’s Hospital of Michigan, Detroit Medical Center, Wayne State University School of Medicine, Detroit, MI, USA
injury that tends to be of greater severity than that in adults. Several anatomical differences between the pediatric and adult kidney have been implicated as the etiology for this observed difference: the relatively larger in size and lower position in the abdomen in children, relative paucity of perirenal fat, weaker abdominal wall muscles, more elastic ribs [1–3]. Additionally, the potential cleavage planes presented by persistent fetal lobation of the kidneys increase the risk of renal laceration . It has been postulated that pre-existing renal abnormalities resulting in abnormal renal size, position or parenchymal consistency predispose the kidney to injury, even following relatively low-force traumatic injuries [1, 3–6]. Blunt abdominal trauma accounts for nearly 90% of renal injuries in children ; Broghammer et al.  reported the three most common mechanisms of injury associated with blunt abdominal trauma in children as motor vehicle accidents, motor vehicle vs. pedestrian and falls from height. Two separate studies report 12.6% and 15.4% of kidney injuries in children occur in the setting of pre-existing renal anomalies [3, 9]. Despite this not insignificant figure, the mechanism for increased susceptibility of abnormal kidneys to injury remains unclear. Rapid deceleration forces encountered with blunt abdominal trauma predispose children to ureteropelvic junction or vascular pedicle injury, especially when the kidney is abnormally enlarged [1, 10–12]. Direct compressive forces can compress the kidney if it is displaced from its relatively protected position in the retroperitoneum by processes where the kidney is abnormally enlarged (hydronephrosis, cystic renal disease or a renal mass) or from failure of normal ascension of the metanephros (crossed-fused renal ectopia, horseshoe kidneys). Computer simulations have shown that elevated pressure within a hydronephrotic renal pelvis amplifies the force of impact, thus increasing the probability of tissue injury . Application of trauma guidelines for imaging injured children has proven difficult; numerous studies have illustrated a
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disconnect between the clinical presentation and the presence and severity of renal injury [5, 7, 13–16]. When the traumatic injury is relatively minor, US is the most appropriate initial imaging modality in children. In children with more severe injuries, CT is the preferred modality and should always be performed in accordance with ALARA principles. Contrast dose timing for trauma-protocol CT examination is generally during the nephrogenic phase; judicious selection of which patients receive delayed scanning or pre-dosing of intravenous contrast help to limit the dose of ionizing radiation when evaluating for urine leak [17, 18]. Follow-up imaging is best accomplished with US or potentially MR-Urography to further reduce exposure to ionizing radiation. The presence of pre-existing renal pathology can have a significant impact on trauma management; accurate imaging diagnosis is of paramount importance to determine the severity of solid organ injury and guide the clinician as to whether surgery or conservative management is needed [6, 8]. Though conservative management for severe renal injuries has been shown to be effective, the presence of pre-existing renal pathology may alter the treatment plan or even prohibit nonoperative management [5, 14, 19].
which suggest chronicity of the hydronephrosis (Fig. 1). Collecting system disruption decompresses the hydronephrotic kidney, which results in a perinephric fluid collection representing urinoma. The pre-existing collecting system dilatation may be exacerbated when a blood clot acutely obstructs the ureteropelvic junction (Fig. 2). Coexistent hemorrhage may increase the size of the perinephric collection; the renal injury may therefore be misinterpreted as more severe. Parenchymal hematoma may be simulated by hemorrhage into a dilated calyx (Fig. 3). Distortion of the kidney anatomy by the underlying congenital hydronephrosis or the perinephric collection may erroneously suggest higher grade of renal injury. Though pyeloplasty may be desired as definitive treatment, measures such as nephrostomy or ureterostomy placement may be utilized to alleviate acute hydronephrosis due to a thrombus. Recognition of the anatomical distortion due to the UPJ obstruction is important to avoid misplacement of temporizing drains into the perirenal collection, which could then prevent its tamponade.
Polycystic kidney disease
The most common site of congenital urinary tract obstruction is at the ureteropelvic junction (UPJ). It occurs more frequently in boys and may be bilateral in up to 25% of cases . The typical imaging findings include hydronephrosis without hydroureter and, when long-standing and severe, renal parenchymal thinning. The degree of obstruction and its implication of renal function may be further assessed with nuclear medicine or contrast-enhanced cross-sectional imaging modalities (notably MR Urography). Important clues to correctly diagnosing pre-existing hydronephrosis in an injured kidney include renal enlargement and parenchymal thinning, both of
Autosomal recessive polycystic kidney disease (ARPKD) is the most common inherited cystic renal disorder in infants and children, occurring in 1 in 20,000 live births. Although autosomal dominant polycystic kidney disease (ADPKD) is more common overall with an incidence of 2 in 1,000 live births, it may not become clinically or radiographically apparent until later in childhood or during adult life. While there may be some overlap of imaging features of the different types of polycystic kidney disease early in life, ARPKD presents in infancy with symmetrically enlarged kidneys, typically much greater than two standard deviations above normal for age, with abnormally echogenic renal parenchyma. ADPKD presents later in life with larger discrete cysts interspersed between normal-appearing intervening renal parenchyma [21, 22].
Fig. 1 A 10-year-old girl with abdominal pain and gross hematuria following minor abdominal injury. a Contrast-enhanced CT image demonstrates moderate right hydronephrosis and a large perinephric fluid collection, most consistent with combined urinoma and hematoma (stars). Note diffuse renal cortical thinning. b Contrast-enhanced CT
performed 1 week later shows near-resolution of the urinoma/hematoma. There is now severe right hydronephrosis with renal cortical thinning again noted. c On delayed imaging sequences, filling defects are visible within the right renal collecting system (arrows) representing residual blood clots
Ureteropelvic junction obstruction
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Fig. 2 A 10-year-old girl with abdominal pain following a minor abdominal injury. She presented to the emergency department after developing hematuria the following day. Axial (a) early and (b) delayed phase contrast-enhanced images from a CT demonstrate severe left hydronephrosis with cortical thinning and a non-dilated left ureter,
consistent with a congenital left ureteropelvic junction obstruction. The low-density collection (stars) about the renal hilum and at the lower pole of the left kidney likely represents a combination of urinoma and hematoma given density greater than expected for urine, though no active extravasation of contrast was demonstrated
Enlarged, polycystic kidneys may project inferiorly beyond the renal fossa, exposing the kidneys to greater risk of injury by providing both a larger target and potential cleavage planes for the energy encountered with blunt abdominal. Cyst rupture results in a perinephric fluid collection of variable size whose imaging characteristics are of simple fluid . Hemorrhage into pre-existing cysts in ADPKD may present as echogenic debris within the cysts (Fig. 4) or approximate the attenuation of normal intervening parenchyma on contrast-enhanced CT (Fig. 5). It is important to note that hemorrhage into a cyst may be related to a remote traumatic event. ARPKD may also present with non-shadowing echogenic foci on US, representing calcium citrate deposition but simulating hemorrhage .
and the horseshoe kidney. In crossed renal ectopia both kidneys are located on the same side of the spine, usually with the crossed kidney located inferiorly. In 90% of cases, there is parenchymal and fascial continuity between the two kidneys, in which case the term crossed-fused renal ectopia is applied. Horseshoe kidneys remain on their respective sides of the abdomen, and are usually joined between their inferior poles by an isthmus of parenchyma or fibrous tissue and may not ascend into the upper abdomen to the renal fossa . As with other congenital anomalies of the kidney, an ectopic kidney is less protected due to lack of the anatomical shielding in the normal renal fossa [6, 10]. Midline ectopic kidneys or the isthmus of a horseshoe kidney may be injured when compressed against the spine, which is often difficult to resolve with US due to the overlying bowel  (Fig. 6). Anomalous course of the renal vessels and the ureters is commonly associated with renal ectopia and may predispose these structures to injury, resulting in perinephric collections from a combination of urinoma and hematoma. Care should also be taken to differentiate the multiple renal vessels and more superficial collecting system structures overlying the ectopic kidney from perinephric hemorrhage.
Renal ectopia Abnormal ascension of the fetal metanephros results in renal ectopia. Ectopic kidneys can be located anywhere between the pelvis and the normal renal fossa, with the majority in the pelvis. Two notable variations of congenital anomalies of renal migration include crossed renal ectopia
Fig. 3 A 12-year-old boy with flank pain and gross hematuria after being tackled during a football game. Axial (a) and coronal (b) images from a contrast-enhanced CT show severe right hydronephrosis and renal cortical thinning consistent with a congenital UPJ obstruction. Hemorrhage
into the collecting system manifests as mixed-density attenuation (arrows). Perinephric fluid represents a combination of urinoma and hematoma (stars)
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Fig. 4 A 12-year-old girl with a known history of autosomal dominant polycystic renal disease who had hematuria following a motor vehicle accident. a Axial unenhanced CT image demonstrates enlarged kidneys with innumerable cysts of varying size, two with hyperdense attenuation
consistent with hemorrhage. b Following contrast administration, the hemorrhage is similar in attenuation to the normal enhancing renal parenchyma (curved arrows)
Fig. 5 A 16-year-old boy with known autosomal dominant polycystic kidney disease who presented to the emergency department with painless gross hematuria. Longitudinal (a) and transverse (b) sonograms of the left kidney demonstrate multiple cysts of variable sizes, some containing echogenic debris consistent with intracystic hemorrhage (arrows)
Renal masses There are a multitude of renal masses that occur in children, though a detailed discussion of these masses is beyond the scope of this article. The most common renal malignancy in children is Wilms tumor; other less common pediatric renal tumors include clear cell sarcoma, renal cell carcinoma, renal lymphoma and atypical teratoid-rhabdoid tumor. Congenital mesoblastic nephroma is most often seen in children younger
than 12 months. Children with tuberous sclerosis may have angiomyolipomas, which have a tendency to hemorrhage, especially with increasing size . Though discovery of a renal tumor following trauma may fortuitously lead to earlier diagnosis, it is important to recognize that the imaging manifestations of a traumatized kidney with a pre-existing mass are often out of proportion to the trauma. Schmidlin et al.  proposed renal tumors decrease tissue resistance of the kidney thus affording the organ less
Fig. 6 A child with blunt abdominal trauma. Axial (a, b) and reconstructed coronal oblique (c) images demonstrate a crossed-fused ectopic right kidney with incomplete laceration (arrow) and a large retroperitoneal hematoma (stars)
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Fig. 7 A newborn boy born with a distended abdomen and anemia. Axial contrast-enhanced CT images (a, b, c) demonstrate a large, heterogenous right renal tumor (arrows) with an adjacent intermediate-density
collection (stars). The tumor was later confirmed to be a neonatal Wilms tumor with intrapartum extraperitoneal and intraperitoneal rupture
protection during trauma; additionally, large tumors tend to displace the kidney from the renal fossa, which predisposes the kidney laceration or fracture. New vessels created by tumor-induced angioneogenesis tend to be fragile and hemorrhage from relatively minor injuries (Figs. 7 and 8). Tumor necrosis or intratumoral hemorrhage may look similar to a hematoma (Figs. 8 and 9). If a mass obstructs urine outflow, there is greater risk of collecting system injury as also seen
with UPJ obstruction. Major vascular injury is more likely when the mass stretches the renal pedicle. Accurate tumor staging is challenging when the affected kidney is injured. Surgery is curative in stage I Wilms tumor, where the capsule is intact and there is no vascular invasion; the presence of perinephric tumor or intra- or extraperitoneal spread necessarily upstages the tumor and precludes an otherwise curative nephrectomy. Accurate measurement of a
Fig. 8 A 2-year-old boy who tripped at the park, landing first on all fours and then onto his abdomen. He subsequently complained of abdominal pain and vomited. He also appeared pale and, according to his parent, he was “not behaving like himself.” Axial (a) and coronal (b) contrast-enhanced CT images demonstrate a very large right renal tumor with mixed-density attenuation (arrows). The normal renal parenchyma is compressed medially (curved arrows). A small perinephric fluid collection represents hemorrhage (stars). The patient was stabilized hemodynamically and subsequently underwent successful pre-nephrectomy catheter embolization of the right kidney with alcohol (c, d). Right nephrectomy was then performed; the pathology was favorable histology Wilms tumor (stage 3)
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Fig. 9 A 15-year-old boy with persistent abdominal pain 2 weeks after falling onto his bicycle handlebars. Contrast-enhanced CT images (a, b) demonstrate an extensively necrotic neoplasm of the lower pole of the left
kidney (arrows). A thin rim of mixed-density fluid (stars) around the tumor suggests rupture and hematoma, which were documented at nephrectomy. The pathology diagnosis was renal cell carcinoma
fractured renal cell carcinoma as part of its accurate staging may be difficult, and as with Wilms tumor, spillage of tumor into the perinephric fat and beyond increases the tumor stage.
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Conclusion Pediatric kidneys are more prone to injury following blunt abdominal trauma than adult kidneys due to anatomical differences in children. The presence of pre-existing abnormalities may increase the risk of renal injury, often manifesting as more severe damage than would normally be dictated by the mechanism of injury. Trauma to a kidney with a pre-existing lesion often presents with complex and confusing imaging features. Knowledge of and consideration for the presence of pre-existing renal lesions by the interpreting radiologist is therefore paramount to correctly diagnosing both the injury and the pre-existing abnormality, which ultimately has significant impact on trauma management for the clinician. Conflicts of interest None
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