Question 1

B. Correct! This is an angiomyolipoma (AML). Images demonstrate a lesion containing macroscopic fat arising from the lateral aspect of the left kidney. Macroscopic fat typically demonstrates loss of signal on fat-suppressed images. Microscopic fat does not demonstrate loss of signal on fat-suppressed images; rather, it exhibits a loss of signal between in- and out-of-phase chemical shift imaging. The components of an AML include blood vessels (angio), smooth muscle (myo), and fat (lipoma).

Other choices and discussion

A. A myelolipoma is typically a macroscopic fat-containing lesion of the adrenal gland. In this case, the lesion clearly arises from the kidney. Note the “claw” sign. The “claw” represents normal renal parenchyma around the lesion, suggesting the organ of origin.

C. In this anatomic region, liposarcomas generally arise from the retroperitoneum and exert mass effect on the kidney. They rarely arise de novo from the kidney. Liposarcomas are usually hypovascular. The key to making the diagnosis of liposarcoma is determining that the site of origin is the retroperitoneum rather than the kidney.

D. Although 5% of RCCs contain fat, that fat is usually microscopic. Sonographically, however, AML and RCC may be indistinguishable. In some challenging cases, a lipid-poor AML may be indistinguishable from RCC with any type of imaging, and surgery may be indicated to exclude RCC.

Question 2

C. Correct! Embolization/ablation is recommended. The greatest risk for an AML is hemorrhage. The risk increases when the lesion reaches 4 cm in size or when the patient is pregnant.

Other choices and discussion

A. Conservative management with imaging is acceptable if the lesion is small (< 4 cm) and the patent is asymptomatic.

B. This lesion is benign but its size warrants treatment.

D. This lesion is usually successfully treated with embolization and ablation, which have lower risks than surgery.

Question 3

A. Correct! Renal AMLs are associated with TS. TS, also known as Bourneville disease, is a neurocutaneous disorder. A total of 20% of all AMLs are associated with TS, and up to 75% of individuals with TS have AMLs. When associated with TS, AMLs tend to be bilateral and multiple. Classically, TS is associated with the triad of mental retardation, seizures, and adenoma sebaceum. However, that classic triad is often absent. Other manifestations of TS include facial angiofibromas, cortical/subcortical tubers, subependymal giant cell astrocytomas, lymphangiomyomatosis of the lungs, and cardiac rhabdomyomas. This disorder is inherited in an autosomal dominant fashion but can be sporadic.

Other choices and discussion

B. Von Hippel-Lindau is associated with multiple renal/liver/pancreatic cysts as well as clear cell–type RCC. There is an increased risk of pheochromocytoma, papillary cystadenoma of the epididymis, and pancreatic neoplasms (serious cystadenoma and islet cell tumors). There is an association with central nervous system hemangioblastomas and retinal angiomas. This disorder can be inherited (autosomal dominant) or sporadic.

C. Neurofibromatosis 2 is an autosomal dominant condition classically associated with multiple schwannomas, meningiomas, and ependymomas.

D. Birt-Hogg-Dube syndrome is an autosomal dominant multisystem disease involving the kidneys, skin, and lung. It is characterized by multiple bilateral renal tumors (chromophobe/clear cell RCC and oncocytoma), multiple lung cysts (with an increased risk of spontaneous pneumothorax), and cutaneous lesions (papules and angiofibromas).

Question 1

C. Correct! This is a teratoma. A mature teratoma is a slowly growing ovarian tumor having at least two of the three germ cell layers. In this case, the computed tomography (CT) demonstrates fat density (matching the density of the surrounding pelvic fat) and soft tissue density. Although CT and magnetic resonance imaging are excellent at diagnosing a teratoma, ultrasound is the modality of choice because of its convenience, lack of ionizing radiation, and high accuracy. Ultrasound typically demonstrates a cystic adnexal mass with mural components, often including an echogenic mass with posterior shadowing.

Other choices and discussion

A. A hemorrhagic cyst would not demonstrate fat on CT. On ultrasound, a hemorrhagic cyst appears as a complex cyst with internal blood products. Acute blood is hyperechoic and becomes increasingly hypoechoic over time.

B. An endometrioma would not demonstrate fat on CT. Its appearance on ultrasound can mimic that of a hemorrhagic cyst.

D. Ovarian serous cystadenomas do not contain fat. They tend to be cystic, large, and often bilateral. In addition, they are more common in older women.

Question 2

C. Correct! Torsion is the most common complication of a teratoma, occuring in 5 to 15% of cases. For this reason, these masses are often resected when they are large. The risk of torsion increases once the ovary reaches 5 cm in size.

Other choices and discussion

A. The rate of malignant transformation is < 2%. It can occur in any of the three germ cell layers (ectoderm, mesoderm, and endoderm). Squamous cell carcinoma arising from the lining of the cyst is the most common type. Factors associated with malignant transformation of a dermoid include patient age > 45 years, tumors > 10 cm, elevated serum tumor markers, and a predominantly enhancing soft tissue component.

B. Hemorrhage is a rare complication.

D. Rupture is a rare complication (1 to 4% of patients). Infection is also a rare complication.

Question 3

A. Correct! This is a Rokitansky nodule, which is also referred to as a dermoid plug. It is typically composed of hair, dermal elements, teeth, and/or sebacious material. A Rokitansky nodule has an echogenic and nodular appearance on ultrasound.

Other choices and discussion

B. Calcification can contribute to (but is not the only component of) the Rokitansky nodule.

C. If the lesion were simply a cyst with blood products, a retracted clot would be the correct choice. However, the additional elements shown on CT confirm a teratoma.

D. Fat can contribute to (but is not the only component of) the Rokitansky nodule.

Question 1

B. Correct! This is an intraperitoneal bladder rupture. The initial images demonstrate thickening of the superior bladder wall with adjacent fluid, and the delayed images demonstrate contrast surrounding loops of bowel with tracking into the paracolic gutters. Intraperitoneal bladder rupture represents 10 to 20% of all bladder injuries. It occurs with individuals that sustain a direct blow to a distended urinary bladder. On imaging, extravasated contrast insinuates between bowel loops. This is known as a type 2 injury by cystography.

Other choices and discussion

A. There is no evidence of bowel injury. The density of the contrast within the abdomen on the delayed images matches that in the ureter, confirming its origin from the urinary system/bladder. Additionally, there is no oral contrast on these images. The standard computed tomography protocol for blunt abdominal trauma is computed tomography of the abdomen and pelvis with intravenous contrast but no oral contrast.

C. Extraperitoneal bladder rupture is the most common type of bladder injury (80 to 90%). It is most often associated with pelvic fractures or penetrating trauma. Extravasated contrast tends to accumulate within the prevesicle space (also known as the retropubic space or space of Retzius). This is known as a type 4 injury by cystography.

D. A ruptured hemorrhagic cyst would not produce such extensive and dense fluid throughout the abdomen. Furthurmore, this would not account for the irregular morphology of the bladder on the coronal image.

Question 2

B. Correct! Intraperitoneal bladder rupture requires surgery. Given the risk of chemical peritonitis, there is significant potential morbidity if the defect is not surgically corrected.

Other choices and discussion

A. Conservative management is only appropriate for extraperitoneal bladder rupture.

C. Radical cystectomy is a drastic measure and represents major surgery. In most cases, the urinary bladder is salvagable following trauma.

D. An indwelling Foley catheter is the treatment for extraperitoneal bladder rupture.

Question 3

C. Correct! The gravity method allows the least traumatic direct entry for contrast. Contrast administration should stop when the patient feels full or can no longer tolerate the instillation.

Other choices and discussion

A. Manually injecting contrast is too intrusive and may cause additional injury/discomfort.

B. Power injecting contrast is too intrusive and may cause additional injury/discomfort.

D. The indirect method of intravenous contrast administration would not ensure optimal urinary bladder filling, and a significant finding might potentially be missed.

Question 1

A. Correct! This is the classic appearance for a multilocular cystic nephroma. Multilocular cystic nephroma (MLCN) is typically encapsulated, T2 hyperintense, herniates into the renal pelvis, and has variable septal enhancement. This lesion has a bimodal age distribution which includes young men and middle-aged women.

Other choices and discussion

B. Hemorrhagic cysts are typically homogenously T1 hyperintense and nonenhancing.

C. This could represent a cystic RCC. Although it does have the the classic appearance of a MLCN, RCC is much more common than MLCN. These two lesions are often difficult to differentiate by imaging, and both lesions are often resected.

D. Oncocytomas are large, well-demarcated lesions that are less cystic than the test case. They classically have a nonenhancing central stellate scar (which is T2 hypointense), a finding seen in 30% of cases. Relatively homogeneous enhancement is common. Oncocytomas can be multiple and bilateral. There is also an association of oncocytomas with tuberous sclerosis and Birt-Hogg-Dube.

Question 2

C. Correct! This is Bosniak 3. Bosniak 3 lesions are indeterminate for malignancy and usually require resection or ablation. Key findings of Bosniak 3 lesions include thick/nodular septa and a wall with measurable enhancement (both are seen here). Malignant potential is 55%.

Other choices and discussion

A. Boniak 1 lesions are simple cysts with imperceptible walls. There is no malignant potential, and follow up is not necessary.

B. Bosniak 2 lesions are minimally complex cysts. These include hemorrhagic cysts < 3 cm, cysts with few thin septations (< 1 mm), and cysts with thin calcifications. There is no malignant potential, and follow up is not necessary.

Bosniak 2F lesions are slightly more complex cysts. These include hemorrhagic cysts > 3 cm in size, an increased number of (or minimal thickening of) septa, and nodular or thickened calcifications, but still no measurable contrast enhancement. The malignant potential is 5%. These require follow up at 6 months.

D. Bosniak 4 lesions are clearly malignant. These includes cysts with a solid-enhancing nodule or mass.

Question 3

B. Correct! Resection is the treatment of choice.

Other choices and discussion

A. While this entity is benign, it is not readily distinguished from RCC by imaging, and observation could be a mistake.

C. Embolization is not the standard of care. If performed, embolization is generally reserved for small tumors. One drawback of embolization is that it would probably require multiple treatments, thus prolonging the time period for therapy. In addition, because malignancy is not definitively excluded by imaging, resection is indicated.

D. Further imaging would not result in a more definitive diagnosis.

Question 1

C. Correct! The patient has a urethral diverticulum. These occur posterolateral to the urethra and above the level of the pubic symphysis. They can grow and surround the ureter posteriorly (“Saddlebag” morphology), as in this case. Symptoms include dysuria, dribbling, and dysparunia (the 3 Ds) as well as urinary frequency and urgency. A connection to the urethral lumen is demonstrated in most cases.

Other choices and discussion

A. Bartholin gland cysts typically occur posterior to the lower vagina and below the level of the pubic symphysis. They are associated with the labia majora and result from chronic inflammation leading to ductal obstruction. These cysts are usually asymptomatic but may require drainage due to superimposed infection.

B. Skene gland cysts are rentention cysts that form secondary to inflammation/obstruction of the paraurethral ducts. These are typically located lateral to the external urethral meatus and below the level of the pubic symphysis. Skene gland cysts are usually asymptomatic but may require drainage or excision due to superimposed infection.

D. Gartner duct cysts typically occur anterior to the superior vagina and above the level of the inferiormost aspect of the pubic symphysis. They result from the incomplete regression of the wolffian ducts. When Gartner duct cysts are located at the level of the urethra, they can cause mass effect on the urethra, giving rise to urinary tract symptoms.

Question 2

A. Correct! T2 is the MRI sequence of choice and should be obtained in all three planes. T2 is the most sensitive for the detection of small cystic lesions. MRI is the current test of choice for the diagnosis of urethral diverticulum. Historically, either contrast-enhanced radiography (voiding cystourethrography or double-balloon urethrography) or fiberoptic urethroscopy were used to make the diagnosis. However, these methods are invasive, difficult to perform, and uncomfortable for the patient. Additionally, if the urethral diverticulum contains hemorrhage, pus, or stones, the diverticulum may be missed.

Other choices and discussion

B. T1-weighted sequence is less sensitive than T2 for the detection of small cystic lesions. However, T1 is useful in detecting the sometimes-found internal hemorrhage.

C. Postcontrast images are less sensitive than T2 for making this diagnosis. However, contrast is useful in detecting underlying inflammation, infection, or malignancy.

D. Diffusion-weighted imaging is not the sequence of choice. However, diffusion-weighted imaging is to supplement the detection of underlying infection/malignancy.

Question 3

B. Correct! Adenocarcinoma is the most common cancer type to arise within a urethral diverticulum. Note that the overall incidence of malignancy within a diverticulum is low. Adenocarcinoma also occurs within urachal remnants and diverticula.

Other choices and discussion

A. Transitional cell carcinoma is the most common cell type in the genitourinary tract and is found most commonly within the bladder, urethra, and ureters.

C. Sqamous cell carcinoma is not common within the genitourinary tract. About 5% of bladder cancers are of squamous cell origin.

D. Small cell carcinoma is not common within the genitourinary tract.

Question 1

C. Correct! This is a case of transitional cell carcinoma (TCC). This is the classic appearance of a ureteral tumor by plain film urography, with the formation of a meniscus or a “goblet” sign. The lack of upstream ureteral dilatation suggests that this process developed slowly. TCC is most commonly found in an older population (average age of 65) with a 4:1 predilection for males. A total of 96% of cases are found in the urinary bladder, 3% in the renal pelvis, and 1% in the ureter. These tumors are usually characterized as either papillary or nonpapillary.

Other choices and discussion

A. Renal calculus is unlikely given lack of upstream dilation, which would be expected with a stone of this size. In addition, this stone would have to be radiolucent, and a stone would not produce the meniscus effect seen here.

B. A blood clot of this size would be expected to cause upstream dilatation of the collecting system.

D. RCC is extremely rare in the ureter.

Question 2

A. Correct! Risk factors and industrial exposures linked to TCC cancer development include smoking, certain amine and phenyl dyes, cyclophosphamide, phenacetin, and aristolochic acid (Balkan nephropathy).

The other choices are all incorrect.

Question 3

B. Correct! Metachronous tumors of the urinary tract are more common with upper urinary tract TCC. Metachronous tumors are those that occur at different times. Approximately 40% of patients with upper urinary tract TCC will develop additional sites of tumor distally (usually in the bladder). The surgical treatment of choice for an upper tract TCC (involving the kidney or ureter) is a nephroureterectomy (where the ipsilateral kidney and ureter are removed).

Other choices and discussion

A. Only 2 to 4% of patients with bladder TCC develop tumor elsewhere within the urinary tract. Surgical treatment for bladder TCC typically consists of radical cystectomy with ileal conduit formation. (The bladder is first removed. Then a portion of the ileum is removed and connected to the ureters to serve as the urinary bladder.) The conduit drains through an ostomy.

C. Urethral TCC is extremely rare. Most carcinomas of the urethra are squamous cell.

D. There is an increased risk of metachronous RCC in patients von Hippel-Lindau disease, patients diagnosed with RCC before the age of 40, and patients with familial RCC.

Question 1

B. Correct! This is a duplex kidney. The first image demonstrates a cystic structure in the left upper pole, which is contiguous with the dilated ureter seen on the magnetic resonance urogram (second image). There is also focal atrophy at the upper pole of the left kidney. This atrophy is the result of chronic obstruction. The remaining lower portion of the kidney is normal and has a nondilated collecting system. These are all typical findings of a duplicated collecting system with two ureters. The visible ureter is dilated and extends from the upper pole moiety. The ureter of the lower pole moiety is not visible. A duplicated system is one of the most common congenital renal anomalies. The extent of duplication is on a spectrum. It may be a simple as duplication of only the renal pelvis, draining with a single ureter, or two distinct collecting systems that drain into the bladder. When the latter occurs, the anatomy usually follows the Weigert-Meyer rule (see below). Duplication is seen in 0.7% of the population, and mild forms are often overlooked with imaging. Most cases are asymptomatic, but complications of infection, obstruction, and reflux sometimes occur.

Other choices and discussion

A. If a left ureterovesical junction stone were to cause this degree of ureteral dilatation, atrophy of the entire kidney would be expected. Additionally, given lack of perinephric edema, this process appears to be chronic.

C. A congenital megaureter could be the answer, if a normal collecting system wasn’t visualized in the lower portion of the left kidney. A true primary congenital megaureter is related to a distal adynamic segment with proximal dilatation. This is analogous to primary achalasia in the esophagus. This entity is often diagnosed in children. This can rarely be associated with congenital megacalyces. Vesicoureteric reflux can also result in ureteral dilatation.

D. The cystic structure in the first image is a part of the dilated collecting system. A renal sinus cyst does not connect to the renal pelvis and collecting system.

Question 2

C. Correct! The upper pole obstructs and lower pole refluxes. According to the Weigert-Meyer law, the lower pole ureter inserts orthotopically (in its normal location), and the upper pole ureter inserts ectopically, inferiorly, and medially relative to the lower pole ureter. The ectopic insertion is often associated with a ureterocele, which can cause obstruction of the upper pole moiety. There is often distortion of the ectopic ureter insertion, resulting in reflux. On pyelogram, sometimes only the lower pole opacifies (due to upper pole obstruction). Mass affect from the dilated upper pole forms the classic “drooping lily” sign.

The other choices are incorrect.

Question 3

B. Correct! Use of contrast to confirm or exclude communication of the “cyst” with the collecting system is the best way to differentiate a renal sinus cyst from hydronephrosis. (A cystic structure filling with contrast that subsequently passes into the collecting system does not represent a renal sinus cyst.) In terms of which contrast study to select, the important point is to be able to compare precontrast to postcontrast, possibly including delayed imaging. Of the answer choices, multiphase CT is the best option.

A multiphase magnetic resonance imaging study is equally as effective as a contrast-enhanced CT for this purpose.

Note that a cystic structure in this region that opacifies could represent either hydronephrosis or a calyceal diverticulum, which also communicates with the collecting system. The morphology should be able to differentiate these choices.

Other choices and discussion

A. Renal ultrasound can often (but not always) differentiate parapelvic cysts from hydronephrosis.

C. A single phase of a contrast study can have limitations in making this diagnosis.

D. An intravenous pyelogram can demonstrate hydronephrosis and can often demonstrate deformities of the collecting system by adjacent renal sinus cysts, but the anatomic assessment is limited and intravenous pyelogram cannot demonstrate the cysts themselves.

Question 1

A. Correct! The kidneys are not in their expected location on these images, and a fused kidney is seen in the right lower quadrant. This is the characteristic appearance of crossed-fused renal ectopia. Computed tomography depicts the parenchymal band connecting the kidneys. Potential complications of this anomaly include nephrolithiasis, infection, and hydronephrosis. Crossed fused renal ectopia results from abnormal renal ascent in embryogenesis. Normally by the eighth week of life, the kidneys reach their appropriate position at the L2 level.

Other choices and discussion

B. A duplicated collecting system would not explain both the absence of a contralateral kidney and the pelvic kidney location.

C. A horseshoe kidney refers to fusion of both kidneys (either with a parenchymal or a fibrous band) with the respective kidneys remaining on their own side. With a horseshoe kidney, the inferior pole of each kidney is medially positioned while the superior pole is laterally positioned. This is the reverse of normotopic kidneys.

D. While the right kidney is low lying, a pelvic kidney is an incomplete diagnosis. Additionally, this would not account for the fusion of the kidneys.

Question 2

C. Correct! The abnormally fused kidney’s ureter inserts into its normal location (orthotopically); in this case, on the left side of the bladder.

Other choices and discussion

A. An inferior insertion of the ureter may be seen with a duplicated renal collecting system.

B. A fused insertion with the right ureter might occur along the spectrum of a duplicated collecting system.

D is incorrect.

Question 3

B. Correct! Renal agenesis can be association with a number of chromosomal anomalies, including Down syndrome and Turner syndrome.

C. Correct! Unilateral renal agenesis is commonly associated with müllerian duct anomalies.

Renal agenesis results from absence of induction of the metanephros by the ureteral bud at 6 to 7 weeks gestation. The metanephros becomes the adult kidney, and absence of its formation results in the complete absence of the structure. The metanephros is also important for normal internal genital formation, explaining the association of renal anomalies with wolffian and müllerian duct anomalies. In the absence of a kidney, always check the pelvic structures, as uterine anomalies in females and ipsilateral seminal vesicle agenesis in males are commonly associated. Adrenal agenesis is extremely rare and can be associated with renal agenesis.

Other choices and discussion

A. Caroli disease is a congenital disorder with multifocal cystic dilatation of the segmental intrahepatic bile ducts. It is associated with autosomal recessive and autosomal dominant polycystic kidney disease as well as medullary sponge kidney.

D. Budd-Chiari is hepatic venous obstruction and is not associated with renal agenesis.