Small renal masses


Defined as solid cortical neoplasms of the kidney less than 4 cm, and comprise approximately 40% of all newly diagnosed renal tumors and they’re often detected incidentally when working up another medical complaint.

Many patients with small benign masses undergo unnecessary nephrectomy.

Among malignant masses the increasing size correlates with higher pathologic stage.

Growth rate for small renal masses is approximately 2-4 mm/year (Chawla SN et al).

Growth rate for small renal masses is similar for benign and malignant lesions (Siu W et al).

About 30% of small renal masses have no growth over 23-39 months of observation (Chawla SN et al).

Small renal masses that show no growth are as likely to be malignant as benign (Kunkle DA et al)

The smaller the  renal mass the greater the likelihood that it is benign.

Tumors measuring 3 cm or less rarely metastasize and have a slow growth rate.

Indications are small renal masses unsuited for or refusing surgical intervention that were followed found: lesions that were destined to grow fast and metastasize did so early, whereas most small tumors grew at a low rate or not at all (Rendon RA et al).

46% of masses less than 1 cm are benign, 22% of lesions between 1-2.9 cm or benign and 20% of those 30-3.9 cm or benign on the basis of  a review of 2700 and surgical excised solid renal tumorsK (Frank I et al).

The average growth rate of clinically significant renal carcinomas was 2.13 cm/year.



The growth rate of clinically significant renal cancer appears to be higher than the rate reported in surveillance trials. 



Renal tumors tend to grow faster in young patients.

The finding of macroscopic fat within a small  renal mass on CT  or MRI imaging is suggestive of a angiomyolipoma,  a benign  lesion.

The presence of calcification in a small renal mass is suggestive of a malignancy ( Silverman SG et al).

Assessment of small solid renal masses or complex cysts includes evaluating the size, shape and enhancement qualities to determine the presence of a malignancy.

Imaging studies to assess  small renal masses are best performed by renal CT scans or MRI scans.

No clear-cut clinical or radiological characteristics can predict

future growth or histological diagnosis.

Masses that are 70Hounsfields units or larger are likely hemorrhagic or proteinaceous and benign.

Heterogeneous masses with thick or irregular walls require further work up.

Enhancement on CT scan is defined as +20 Hounsfield units after contrast injection and such lesions need additional work up.

A change of less than 20 Hounsfield units likely indicates a cyst.

Most small real lesions that are malignant are low grade.

Papillary masses are not well characterized by CT contrast enhancement.

Three studies of excise regional cancers 3-4 cm in diameter, 14-26%

were grade 3 or  4, and 12-36% invaded perirenal fat (pT3a).

Patients with small renal masses and associated symptoms have a worse prognosis than asymptomatic patients with similar size tumors that are

detected incidentally ( Lee CT et al).

Metastases are present in 1-8 percent of patients with renal cancers measuring  3-4 cm, at the time of diagnosis (Chwala SN).

SEER  data from 1998-2003 showed  a 5.2% prevalence of metastases  at

presentation among 8792 patients with small renal cancers and a 1 cm

increase in the size of the primary cancer increase the prevalence of

metastases by 3.5% (Nguyen MM et al).

CT  guided needle biopsies have a sensitivity for detection of cancer

of 80-92% and a specificity of 83-100% (Volpe A, Shannon BA, Rybicki


Masses less than 3 cm  have a higher  false-negative rate on  needle


Benign,  nondiagnostic or non-malignant masses on needle biopsy  are to be followed with surveillance imaging, possibly repeat biopsy, or surgery.

The addition of  molecular or cytogenetic techniques can improve the accuracy of needle biopsy.

Small  kidney lesions solid or complex cystic type are classified class III or  IV Bosniak type.

T1a tumors are 4cm or less andT1b is 4cm or greater.

T1 a lesions pose little threat to many patients, particularly older patients, because only 60% may run a relatively indolent course, up to 20% are histologically benign, most commonly oncocytomas or atypical variants of angiomyolipomas.

Most T1 lesions are identified in asymptomatic individuals and are found incidentally.

Recent evaluation revealed that the incidence of small kidney cancers T1 has increased by more than 285% and for lesions less than 2 centimeters by 244% into those 2 to 4 cm (Hollingworth D et al ).

Surgical management is reserved for patients who have tumors with rapid doubling times or tumors that are the upper limits of 3-5 cm in greatest dimension.

Small renal masses may be managed with surgical resection, even a partially or radical nephrectomy, thermal ablation or active surveillance.

Active surveillance remains underutilized as an alternative option to primary intervention, employed in only 10-20% of eligible patients. 

Renal biopsy small masses can be characterized as: No risk of metastases with benign tumors such as oncocytoma and angiomyolipoma, low risk of metastases with an indolent tumor such as type I papillary renal cell carcinoma, chromophobe renal cell carcinoma and clear cell papillary renal cell carcinoma and intermediate to high risk of metastasis including clear cell renal cell carcinoma2 papillary renal cell carcinoma and unclassified renal cell carcinoma.

In a systematic review and meta-analysis renal mass biopsy is inaccurate and safe diagnostic procedure (Mrconi L et al).

Ablative procedures are potentially less invasive and associated with less morbidity than extirpative procedures.

Laparoscopic and percutaneous cryoablation have similar favorable oncological outcomes with minimal effect on renal function (Pessoa, R).

A Tc-sestamibi Single photon emission CT enhances the diagnostic performance of conventional imaging and can more readily classify renal masses into benign or indolent and aggressive sub groups.

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