Generally defined as < 4 cm maximal diameter, solid lesion on imaging concerning for RCC.
Mostly incidental on imaging.
Incidence increasing due to more available imaging.
Classify as:
- Malignant, benign or inflammatory
- Solid, simple cystic or complex cystic
The issue with the small renal mass is that many are malignant (but often indolent), some are benign, and imaging cannot reliably distinguish between them.
Surgical treatment is associated with the risk of potentially significant morbidity, and therefore a balance needs to be found between risk of malignancy and risk of overtreatment.
What could it be?
What is the prognosis of a small renal mass?
Over 20 % of masses < 4 cm are benign.
About 40 % of masses < 2 cm are benign.
Clinical T1a tumours (< 4 cm) are typically indolent even if RCC ( ~ 2 % develop metastatic disease).
The main prognostic indicator is size, with larger lesions more likely to be malignant. Men are also more likely to have malignant lesions than women.
Someone is found to have an incidentally found small renal mass. How do you assess the patient?
History:
- Reason for imaging / presenting illness
- Pertinent symptoms – haematuria, flank pain, paraneoplastic symptomatology
- Medical history
- Co-morbidities and threat to life expectancy
- Renal function / history of renal diseases
- Renal risk factors / diabetes / Htn / smoking
- Personal and family history of malignancy
- Medications including anticoagulants
- Frailty and performance status
- Fitness for general anaesthesia
- Surgical history
- Previous abdominal surgery
- Urological history
- Stones, previous renal surgery
Exam:
- Performance status
- Blood pressure
- Abdominal examination (mass, scars) ; body habitus
- Stigmata of hereditary syndromes
Investigations:
- Bloods – Hb, renal function, LFTs, calcium
- Urinalysis – ?haematuria ?protein
Imaging
The goals of imaging are:
- Characterise the mass as best able – to determine risk of malignancy
- Assess for locally advanced, nodal or metastatic disease
- Assess suitability for further treatment options
- Confirm the presence and function of contra-lateral kidney
- Contrast enhanced CT
- MRI
- Ultrasound
- Nuclear medicine
Imaging of the renal mass
CT
- A multi-phase CT provides the most diagnostic information:
- Non contrast, arterial, nephrographic, delayed.
- Enhancement of 20 or more HU is indicative of malignancy (10 – 20 HU indeterminate)
- Areas of negative CT attenuation (-20 HU or less) suggest fat, and AML
MRI
- A good alternative for those who cannot have iodinated contrast (CKD, allergy)
- Enhancement of > 20 % on gadolinium based contrast suggests RCC
- Small risk of NSF with eGFR < 30
- May provide additional information for tumour thrombus, haemorrhagic cyst
Ultrasound
- Good for differentiating cystic vs solid masses
- Contrast enhanced ultrasound emerging role
Nuclear medicine
- DMSA can be useful in distinguishing pseudotumour (will be the same uptake as normal kidney) vs tumour
- FDG PET has limited role due to the uptake of FDG by the kidney and is not recommended in staging
- Sestamibi is taken up by mitochondria, which are in abundance in oncocytomas and also hybrid chromophobe/oncocytic tumours
- PSMA PET has emerging role for ccRCC
Cystic renal masses
There is a strict criteria for renal cysts to be defined as simple on ultrasound – anything not clearly a simple cyst should be further defined with multiphase cross-sectional imaging.
Thin wall
Avascular
Round or oval shape
No internal echoes (anechoic)
Through transmission with strong acoustic shadowing
CT will allow categorisation with Bosniak criteria:
MRI is useful for haemorrhagic cysts (bright on T1), long term surveillance in young people, or people who cannot have CT contrast.
Biopsy is generally unhelpful for cystic masses – poor diagnostic yield and risk of tumour spillage.
What are the treatment options for a small renal mass?
