35 Renal Mass


35 Renal Mass

Steven S. Chua, Chakradhar R. Thupili, Eduardo J. Matta, and Kaustubh G. Shiralkar

35.1 Case 1

A 63-year-old woman presents with lower back and bilateral lower extremity pain. An MRI of the lumbar spine without contrast was performed to evaluate for radiculopathy.

35.1.1 Imaging Impression

An ill-defined right renal mass is incompletely evaluated in this noncontrast lumbar spine MR examination (▶ Fig. 35.1). The appearance is worrisome for malignancy and additional imaging is required.

Fig. 35.1 T2-weighted (a) and T1-weighted (b) axial images of the lumbar spine demonstrate a heterogeneous to hyperintense T2 and a T1 isointense mass within the right kidney, partially seen (yellow arrow). The right renal mass is less apparent and more ill defined in the T1-weighted image.

35.1.2 Diagnostic Testing Needed

Given that an incompletely characterized right renal mass without diagnostic features of a simple cyst is visualized, additional imaging is required and a CT renal mass protocol was subsequently performed with findings compatible with a 6-cm right renal cell carcinoma (RCC) shown in ▶ Fig. 35.2.

Fig. 35.2 A CT renal mass protocol demonstrates a right renal expansile 6-cm hypodense mass in the axial precontrast (a) image, which enhances in the axial (b) and coronal (d) nephrographic phase, showing mild washout in the axial excretory phase (c), compatible with a renal cell carcinoma (RCC). The yellow arrows indicate the right RCC.

35.1.3 Imaging Interpretation

A right expansile 6-cm arterially enhancing renal mass with washout compatible with an RCC.

35.2 Case 2

An 80-year-old woman presents with back pain after a fall. MRI of the lumbar spine without contrast was performed for evaluation.

35.2.1 Imaging Impression

A left renal mass with high T1 and T2 signal is incompletely evaluated by the noncontrast lumbar spine MRI (▶ Fig. 35.3). As the signal intensity of this mass does not follow that of fluid, and it is incompletely imaged, additional imaging is required.

Fig. 35.3 T2-weighted (a) and T1-weighted (b) axial images of the lumbar spine demonstrate a T1 and T2 hyperintense left renal mass measuring about 3.8 cm.

35.2.2 Additional Testing Needed

The finding of a left renal mass without imaging characteristics of a renal cyst on MRI (well-marginated and homogeneously high in signal on T2 and low in signal on T1 weighted images) requires additional imaging to exclude malignancy. If the lesion was detected on a lumbar spine CT without intravenous contrast, incomplete imaging, heterogeneity, or internal density measurements between 20 and 70 HU, it would require additional imaging. The ACR recommends CT scan with and without intravenous contrast or MRI pre- and postcontrast, especially if the lesion is < 1.5 cm. 1 , 2 , 3 Given that the lesion is T1 and T2 hyperintense, there is suggestion of a fat-containing lesion like an angiomyolipoma. If there had been a fat-saturated sequence (frequency selective), the presence of signal loss in the left renal lesion would be compatible with an angiomyolipoma with macroscopic fat. Angiomyolipomas can also contain microscopic fat, and loss of signal in the opposed-phase image in chemical shift MR will confirm that finding.

Unlike microscopic fat-containing RCCs, angiomyolipomas typically do not contain calcifications. Therefore, a fat-containing mass in the kidney without calcifications most likely represent an angiomyolipoma.

Fortunately, a CT with and without contrast was performed about 10 years prior to the MRI and that CT demonstrated a left renal fat-containing lesion with macroscopic fat without calcifications, compatible with a macroscopic fat-containing angiomyolipoma. On the other hand, a lesion with macroscopic fat and calcification within the kidney is highly suspicious for a RCC. No further imaging was necessary, given that the lesion was less than 4 cm. However, if that lesion were larger than 4 cm, there is a propensity for bleeding and the blood supply to these lesions are typically embolized, especially if a renal artery aneurysm is greater than 0.5 cm. 3 , 4

35.2.3 Imaging Interpretation

Left renal lesion containing macroscopic fat, compatible with a 3.8-cm renal angiomyolipoma.

Fig. 35.4 A prior abdomen and pelvis CT performed for abdominal pain showed a macroscopic fat containing left renal lesion measuring about 3.8 cm in the precontrast phase (a), with mild enhancement in the portal venous phase (b). This left renal lesion is compatible with a lipid-rich angiomyolipoma. Given that the mass is less than 4 cm, no further follow-up is necessary.

35.3 Differential Diagnosis

Differential diagnosis (DDx) for lesions of the kidney are presented in ▶ Table 35.1.

Table 35.1 Differential diagnoses (DDx) of renal lesions 5 , 6




This term usually refers to a solid lesion in the kidney and can range from primary renal cell carcinoma (RCC), urothelial cancer, lymphoma, and inflammatory myofibroblastic tumors to metastatic disease. Tumors that metastasize to the kidney include melanoma, solid tumors of the breast, lung, and gastrointestinal and genitourinary systems, More benign-appearing lesions of the kidney include angiomyolipomas and oncocytomas. Angiomyolipomas show macroscopic fat, which will demonstrate loss of signal in fat-saturated (frequency-selective) sequences on MR and may also show microscopic fat, which will demonstrate loss of signal in the opposed-phase sequences (chemical shift type II) in MR, and generally do not contain calcifications, unlike microscopic fat-containing RCCs, which can contain calcification. Oncocytomas may show a stellate scar and enhance avidly, with progressive enhancement.


Pseudotumors include hypertrophied columns of Bertin, an extension of the cortex into the medulla of the kidney, which enhance similar to renal parenchyma on all phases. In addition, the dromedary bulging from the interpolar region of the left kidney and fetal lobulations are also examples. No further follow-ups are required.

Focal infection

Focal pyelonephritis or intrarenal abscesses are also considerations for renal masses. Typically, if pyelonephritis or intrarenal abscesses were discovered on imaging, a follow-up scan after treatment with a CT abdomen and pelvis with contrast is performed.


Pseudoaneurysm of the renal artery or renal vein can have masslike appearance in the kidney especially in noncontrast images. However, on contrast imaging, these lesions follow the enhancement profile of the vessels.


This structure is the most common lesion of the kidney. Cysts can range from benign to complex, classified by the Bosniak criteria 7 on CT or MR imaging. Benign cysts can be simple with fluid, contain varying amounts of proteinaceous or hemorrhage components to minimally complex with septations and thin calcifications, to complex with thickened irregular septations with enhancing nodularities to cystic renal cell carcinoma. Please see Table 35.2 for more details.

Renal sinus cyst

This term refers to cysts found in the renal sinus and include parapelvic cyst (cyst extending from the renal parenchyma into the renal hilum) vs. peripelvic cyst (lymphatic cysts extending from the hilum into the renal cortex), and can mimic hydronephrosis. An excretory phase with contrast in the renal collecting systems can show that hydronephrosis is not present with these cysts not opacifying with contrast as they are not connected to the collecting system.

Calyceal diverticulum

A calyceal diverticulum extends from and is connected to the renal collecting system and will opacify with contrast in the excretory phase of a contrast-enhanced CT/MR examination. Frequently, milk of calcium or calcium deposits can be found in this herniated sac.

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Jun 28, 2020 | Posted by in NEUROLOGICAL IMAGING | Comments Off on 35 Renal Mass

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