Atypical teratoid/rhabdoid tumour (AT/RT) is an aggressive embyronal brain tumour, typically located in the posterior fossa in infants, characterised by rhabdoid cells, heterogeneous enhancement and restricted diffusion.
Description
Atypical teratoid/rhabdoid tumour (AT/RT) is a highly aggressive and malignant central nervous system (CNS) tumour. This neoplasm belongs to the family of embryonal tumours and predominantly affects the paediatric population, with a predilection for infants. It is most commonly located in the posterior fossa in infants and the supratentorial compartment in older children and adults. AT/RTs are characteristically heterogeneous, often demonstrating multiple cellular components, including areas that resemble primitive neuroectodermal tumours, mesenchymal and epithelial components.
Pathogenesis
The pathogenesis of AT/RTs is characterised by mutations in the SMARCB1 (also known as INI1 or hSNF5) or, less commonly, SMARCA4 genes, which encode for components of the SWI/SNF chromatin remodelling complex. This complex regulates gene transcription, and mutations can lead to uncontrolled cell growth and tumour development.
Subtypes
There are three histological variants of AT/RT:
- Classic AT/RT
- Tyrosine kinase (TRK)-rearranged AT/RT
- Epithelioid glioblastoma-like AT/RT
Epidemiology, Risk Factors & Associations
- Predominantly affects children, especially those less than 3 years old
- No known sex predilection
- Associated with mutations in the SMARCB1 or SMARCA4 genes
Clinical Features
- Symptoms depend on the location of the tumour and can include increased intracranial pressure, seizures, or focal neurological deficits
- May present with signs of rapid neurological deterioration due to the aggressive nature of the tumour
Complications
- High risk of metastatic spread within the CNS via the cerebrospinal fluid, with the spine being the most common site
- These tumours are highly malignant and often fatal, with a median survival of less than a year despite aggressive treatment
Pathological Features
Histopathology
- Macroscopic: Tumours are typically large, heterogeneous and may contain areas of necrosis or haemorrhage
- Microscopic: Characterised by rhabdoid cells, which are large cells with eccentric nuclei and prominent nucleoli
Radiological Features
General Features
- Characteristically demonstrates a heterogeneous appearance due to mixed cellular components and possible areas of necrosis or haemorrhage
CT
- Non-contrast: Hyperdense compared to brain parenchyma, may show calcification
- C+ Arterial: Heterogeneous enhancement
MRI
- T1: Isointense to hypointense compared to brain
- T2: Hyperintense
- FLAIR: Hyperintense
- DWI/ADC: Restricted diffusion
- T1 Gad+: Heterogeneous enhancement
Grading and Staging
AT/RTs are classified as WHO grade IV tumours, reflecting their highly aggressive nature. There is no specific staging system as they are primarily CNS tumours.
Diagnosis
Diagnosis is made by a combination of imaging findings and histopathological examination. Immunohistochemical staining for loss of INI1 protein can help confirm the diagnosis.
Differential Diagnosis
- Medulloblastoma: typically in the cerebellum and more common in older children and adolescents, lacks the characteristic rhabdoid cells of AT/RT
- Primitive neuroectodermal tumours: can be very similar histologically but usually occur in older children and adults, lacks the characteristic rhabdoid cells of AT/RT
Management
- Treatment includes aggressive surgical resection, radiation therapy, and chemotherapy. Despite treatment, prognosis remains poor due to the aggressive nature of these tumours.