Rhabdoid tumour of the kidney is a rare, highly aggressive malignancy of early childhood, closely related to atypical teratoid/rhabdoid tumours (AT/RT) of the brain (see rhabdoid tumours).
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Epidemiology
Rhabdoid tumours occur exclusively in children, with 60% occurring before the age of 1 year of age, and 80% before the age of 2 years (average age of presentation = 11 months). Approximately 2% of paediatric renal malignancies are rhabdoid tumours 1.
Clinical presentation
Rhabdoid tumours are very aggressive and initial manifestation may be due to metastatic disease. Local symptoms and signs include haematuria and loin/flank mass. Additionally, patients may develop hypercalcaemia secondary to elevated parathormone levels 1.
Pathology
The term "rhabdoid" stems from the histologic appearance, which resembles that of a tumour of skeletal muscle origin, although in fact, rhabdoid cells are a distinct cellular population. All rhabdoid tumours share deletions in the long arm of chromosome 22, mapped to the INI-1 gene, believed to be a tumour suppressor 3.
Radiographic features
On all modalities, rhabdoid tumours appear as large, centrally located, heterogeneous soft-tissue masses, involving the renal hilum with indistinct margins.
CT
Rhabdoid tumours are large and heterogeneous, usually located centrally within the kidney. They are lobulated with individual lobules separated by intervening areas of decreased attenuation, relating to either previous haemorrhage or necrosis 2. Enhancement is similarly heterogeneous.
Calcification is relatively common, seen in up to 66% of cases 4 and is typically linear and tends to outline tumour lobules 2.
Subcapsular fluid accumulation is said to be a relatively characteristic feature, not often seen in other paediatric renal tumours. Although, due to the rarity of renal rhabdoid tumours, a paediatric renal neoplasm with a subcapsular fluid collection is still more likely to represent Wilms tumour 4.
Treatment and prognosis
Rhabdoid tumours have the worst prognosis of all renal tumours. It is highly aggressive and metastasises early, with up to 80% of patients presenting with metastatic disease, typically to the lungs and less often to the liver, abdomen, brain, lymph nodes, or skeleton 1,2.
Treatment consists of radical nephrectomy and resection of adjacent lymph nodes followed by chemotherapy. Survival is poor, with an 18-month survival rate of only 20%, and almost all patients succumbing before 5 years post-diagnosis 1,2.
Differential diagnosis
The main differential is that of the far more common Wilms tumour. Although imaging appearances can be similar, a number of features can help point towards the diagnosis of a rhabdoid tumour. These include 1,2:
- subcapsular fluid collections
- tumour lobules separated by hypoattenuating areas of necrosis or haemorrhage
- calcifications
- more common than in Wilms tumours (66% in rhabdoid vs 6-15% in Wilms) 2
- typically linear distribution outlining tumour lobules
- vascular and local invasion is more common
- a synchronous intracranial neoplasm is a distinguished feature of rhabdoid tumour 4
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