Five Top Tips for Evaluating a Renal Mass

1) Be familiar with the sonographic appearance of anatomical variants and renal pseudotumours.

Renal pseudotumours are very commonly encountered in ultrasound, particularly hypertrophied columns of Bertin (which are present in approximately half of all adults) and splenic (dromedary) humps.  Pseudomasses can also be secondary to persistent foetal lobulation, renal scarring and following nephron sparing surgery.

Be aware of the grey-scale and colour Doppler criteria for pseudomasses and apply them critically.  In some cases it can be difficult to determine whether there is a true renal mass or whether appearances are due to a pseudomass; in this situation ultrasound contrast microbubble administration (CEUS) can be invaluable for an accurate diagnosis and this is a recommended indication for CEUS in the EFSUMB guidelines (Recommendation 6).[1]

2) Not all solid renal masses are neoplastic: remember infection.

Focal pyelonephritis (lobar nephronia) may produce a focal solid renal mass that can be indistinguishable from a renal tumour.  This may be more echogenic, isoechoic or less echogenic than normal renal cortex, although increased echogenicity is most common.  As ultrasound practitioners we have the opportunity to evaluate the patient’s clinical status directly, where there is the possibility of urosepsis or if the patient is immunocompromised an infective cause should be excluded.  Interval imaging or aspiration/biopsy may be the most appropriate management.

In a patient with severe urosepsis (particularly if diabetic) where the kidney is difficult to identify with ultrasound, consider that this may be due to gas within the renal parenchyma.  Emphysematous pyelonephritis due to a gas-forming infection is a medical emergency – recommend urgent CT evaluation.

3) Beware of the echogenic renal mass.

Approximately a third of all renal cell carcinomas (RCC) are echogenic, the majority of small RCCs are echogenic and some are very echogenic.  Unlike CT and MRI, ultrasound cannot diagnose the presence of fat within a renal mass and therefore cannot differentiate angiomyolipoma (AML) from RCC with certainty.  The presence of an echo-poor rim, calcifications or cystic areas within an echogenic mass is likely to indicate an RCC and acoustic shadowing favours an AML but the bottom line is that CT or MRI is required to categorise all non-calcified echogenic renal masses that are > 1cm in size. 

4) Where multiple or bilateral solid renal masses are identified this is often an indication for renal mass biopsy.

Patients with multiple solid renal masses may still have multifocal RCC (in which cases a hereditary syndrome should be considered, particularly if the patient is young) but there is a wider differential diagnosis.   If the patient has a known visceral malignancy then renal metastases are a strong possibility, particularly if the patient has disseminated disease.  Multiple renal masses may also be the first presentation of patients with lymphoma, the kidneys being a common site of extra-nodal disease, usually in non-Hodgkin lymphoma.

Renal mass biopsy is an established indication for multiple/bilateral renal masses to ensure correct management.

5) Evaluate renal cysts meticulously

Cysts showing more than minimal complexity (one or two fine septa or mild calcification) should be considered suspicious for cystic RCC.   Review any previous renal imaging if available to establish whether the cyst is longstanding and unchanged in complexity, stability over a period of 5 years is required.  An increase in cyst complexity (rather than size) is a worrying feature.  When insufficient historical imaging or increasing cyst complexity is present, additional imaging is usually indicated to assign a Bosniak grade and allow triage to surgery, follow-up or discharge.

CEUS can be very helpful in further categorising complex cysts and is equivalent or superior to CT for this indication (EFSUMB CEUS Guidelines 2017 Recommendation 7).1

[1] The EFSUMB Guidelines and Recommendations for the Clinical

Practice of Contrast-Enhanced Ultrasound (CEUS) in Non-Hepatic

Applications: Update 2017 (Short Version). Sidhu PS et al. Ultrasvhall in Med. 2018;39:154-180