The “Epidemic” of the Small Renal Mass

In this review, we would like to introduce to primary health colleagues the increasing incidence of small renal mass (SRM) in the last decade.

SRMs are typically accepted as any renal mass less than 4 cm in diameter. The greatest reason for this increased incidence is the widespread use of imaging to diagnose other conditions in all sectors of modern healthcare. This new epidemiology of kidney cancer is widely seen throughout Western Europe and North America.1-3 

In Singapore, we have been seeing the phenomenon in the last decade. At the primary care level, where many patients undergo comprehensive health screening, including ultrasound studies of the abdomen, incidentally diagnosed SRMs are now a common clinical problem seen by general practitioners.

From the oncologic standpoint, it is important to note that SRMs are a heterogenous group of lesions and up to 20 to 30% are benign.4-6  

In terms of epidemiology, kidney cancer was the ninth most common cancer in males in Singapore between 2008 to 2012, making up 3.5% of all cancers.7  

It is 1.5 times more common in men than women, with peak incidence between 60 to 70 years of age.8-10 

The majority of cases are sporadic, with only 2-3% being familial, related to conditions such as Von Hippel-Lindau syndrome.11  

The most accepted environmental risk factor for development of RCC is tobacco exposure.11 Obesity and hypertension are other established risk factors.11,12 


Currently, fewer than 10% of RCC present with the classical triad of haematuria, loin pain and a mass.13 

However, up to 20% of patients have evidence of paraneoplastic syndromes, including hypertension, anaemia, polycythaemia, hypercalcaemia, pyrexia and deranged liver enzymes.14  

Thus it is essential to take a detailed medical history and conduct a physical examination. In the current context of SRM, patients are frequently asymptomatic at the point of diagnosis.


The mainstay of evaluation is a detailed contrast-enhanced computer tomography (CT) scan of the kidneys. Alternatively, in patients with renal impairment or contrast allergy, a magnetic resonance imaging (MRI) scan of the kidneys can be performed. Besides assessing the primary tumour and stage of disease, CT scans provide valuable operative information such as renal vascular anatomy, tumour position and status of the contralateral kidney, all of which contribute to the eventual surgical management plan.

Besides imaging studies, the other important determinant of the surgical plan of SRM is the patient’s overall renal function. Besides serum creatinine, the estimated glomerular filtration rate (eGFR) is now frequently used to determine the patient’s renal function, derived from the Modification of Diet in Renal Disease formula, or more commonly known as the MDRD formula.15 

To complete the workup, chest imaging (usually a chest x-ray or CT scan of the thorax) and in some cases, CT scan of the brain or bone scan, may be required to fully stage the disease.


Many patients ask about the role of renal biopsy in the management of SRMs. The sensitivity of a CTguided biopsy ranges from 85- 92%, with a specificity of 85- 100%.16,17  

The risks of bleeding or lung injury are minimal and, more importantly, tumour seeding along the needle track is extremely rare.18 Although the results of renal biopsy are improving, this is not routinely done in all patients with SRM because the diagnostic accuracy of modern CT or MRI imaging is approaching 80-90%.

We reserve renal biopsy for SRM for selected clinical scenarios, namely suspicion of metastasis to the kidney from a concurrent primary tumour elsewhere, suspicion of lymphoma or as a precursor to ablative therapy.



The traditional and gold standard treatment for RCC is a radical nephrectomy (RN). However, studies from the last two decades have demonstrated that RN is associated with progression to chronic kidney disease, greater risk of cardiovascular events and increased mortality.19,20 

Therefore, nephron-sparing strategies such as partial nephrectomy (PN) have emerged as the preferred approach for surgery in all patients with SRM.

PN consists of selective excision of the tumour together with an acceptable margin of normal renal tissue, allowing the preservation of the rest of the kidney. Data has shown that PN has equivalent oncological outcomes compared to RN.21 PN is typically performed with the renal vessels clamped to facilitate excision of the tumour and repair of the kidney defect. It is important that the duration of ischaemia is kept to a minimum to prevent irreversible damage to the nephrons. It is worth mentioning that complication rates of PN are slightly higher than those of RN, mainly due to the increased risk of bleeding, urinary leak and need for repeat operation.21 Local recurrence rate for PN is low, between 1-2%.22,23 

Small Renal Mass Fig 1 - Da Vinci 
Small Renal Mass Fig 2 - Robotic 

At Tan Tock Seng Hospital (TTSH), we offer PN as the treatment of choice for all patients with SRMs who are medically fit for surgery. We now perform PN through minimally invasive approaches, either with conventional laparoscopic technique or advanced robotassisted technique using the Da Vinci Surgical System (figures 1 and 2).

The advantage of robot assistance is that it allows challenging tumours to be removed with a minimally invasive approach. Challenging tumours include those that are endophytic, posterior or centrally-located (figure 3).

A video of robot-assisted partial nephrectomy can be viewed here. Patients can therefore avoid the morbidity of open surgery while receiving nephron-sparing surgery. We have even treated a patient with bilateral synchronous SRMs successfully with staged bilateral robot-assisted PNs (figure 4).

The patient recovered from both operations uneventfully and was discharged on the 3rd postoperative day on both occasions. This surgical approach avoided the morbidity of bilateral flank open incisions.

PN is contraindicated for large tumours which are central in position, because it is difficult to preserve the renal hilum or the main collecting system. In such cases we may perform a RN instead if the patient’s renal function is adequate. In the modern era, virtually all RNs for SRM can be done laparoscopically, offering patients all the benefits of minimallyinvasive surgery, including reduced pain, smaller wounds, shorter hospital stay and earlier return to work.


Ablative therapy is the destruction of tumour tissue using energy sources. This form of treatment has been successfully employed in solid organ tumours such as in the liver and kidney. The two forms of ablative therapy for SRM, radiofrequency ablation (RFA) or cryotherapy, are both available in TTSH.

Ideal patients for ablative therapy have:

  • advanced age or prohibitive co-morbidities at high-risk for major surgery;
  • hereditary RCC with multifocal lesions (eg Von Hippel-Lindau Syndrome); and
  • a tumour in a functionally or anatomically solitary kidney.

There is more data and experience with cryotherapy than RFA. Cryotherapy uses repeated rapid freezing and gradual thawing cycles to cause immediate cellular damage and delayed microcirculatory failure in SRMs. One of the benefits of cryotherapy compared to RFA is that ultrasound can be used to monitor the ‘iceball’ that is generated in real-time, thus ensuring better results with ablation. Studies have reported up to 90-95% success rate with this approach.24,25 

Small Renal Mass Fig 3 - CT Image 

Small Renal Mass Fig 4 - CT Scan 

There is more limited experience with RFA and it can be difficult to monitor the treatment effects in realtime. Radiofrequency waves cause ionic agitation and the generation of temperatures ranging from 50- 100°C, and this results in tissue damage and coagulative necrosis. Some studies have reported 80- 90% success rates with RFA.26 

TTSH was the first hospital in Singapore to perform percutaneous cryotherapy in early 2014. This procedure is done under moderate sedation together with local anaesthetic as an outpatient procedure by the interventional radiologist. This is a valuable option for patients who are otherwise unfit for surgery but require intervention for the SRM. The patients whom we sent for cryoablation were elderly patients with prohibitive risk factors for surgery, whose tumours were increasing in size and therefore unsuitable for active surveillance.

However, it is important to note that the long-term oncologic efficacy of ablative techniques is not well established and it carries significantly higher recurrence rate compared to surgery. Therefore it is important for patients to understand that it is still not the first line treatment of choice SRM.


Studies have shown that the median growth rate of SRM is about 0.28 cm per year, with a 1.2% risk of metastasis during follow-up of patients on active surveillance.22,27  

Preliminary studies have demonstrated that active surveillance can be a possible option for elderly patients or those who are of poor surgical risk due to multiple co-morbidities.22,27  

However, it is usually not recommended for young, surgically fit patients due to the lack of long-term data and the need for frequent surveillance scans and thus radiation exposure. We reserve active surveillance for the few elderly patients who are unfit for surgery with SRM which remain stable in size over a period of time.


In the last decade, kidney cancers are being diagnosed at an earlier stage. A full range of treatment options are available for SRM and these are all available at TTSH. Patients may be overwhelmed by the range of treatment options if they are not counseled appropriately. We hope that through this article, we can engage our primary health partners in helping patients with SRMs understand their condition better and come up with the correct treatment strategy.


  • More than 50% of RCC are detected incidentally nowadays.
  • Small renal masses are defined as renal masses less than 4cm in diameter.
  • About 20% of small renal masses are benign.
  • Contrast-enhanced CT or MRI of the kidneys is required to characterise the tumour.
  • Nephron-sparing strategies should be the standard of care for SRM.
  • PN is the preferred surgical treatment of choice for SRM if technically possible.
  • Alternative options include cryotherapy, RFA and active surveillance.

Article is written by Dr Png Keng Siang. 


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