Atypical Teratoid Rhabdoid Tumor - Diagnosis

Diagnosis

The standard work-up for AT/RT includes:

• MRI Magnetic resonance imaging of the brain and spine
• Lumbar puncture to look for M1 disease
• CT (Computed tomography) of chest and abdomen to check for a tumor
• Bone Marrow Aspiration to check for bone tumors. Sometimes the physician will perform a stem cell transplant
• Bone marrow biopsy
• Bone scan

The initial diagnosis of a tumor is made with a radiographic study (MRI or CT-). If CT was performed first, a MRI is usually performed as the images are often more detailed and may reveal previously undetected metastatic tumors in other locations of the brain. In addition, an MRI of the spine is usually performed. The AT/RT tumor often spreads to the spine. It is difficult to diagnosis AT/RT only from radiographic study; usually a pathologist must perform a cytological or genetic analysis.

Examination of the cerebrospinal fluid is important as one-third of patients will have intracranial dissemination with involvement of the cerebrospinal fluid (CSF). Large tumor cells, eccentricity of the nuclei and prominent nucleoli are consistent findings. Usually only a minority of AT/RT biopsies have Rhabdoid cells, making diagnosis more difficult. Increasingly it is recommended that a genetic analysis be performed on the brain tumor, especially to find if a deletion in the INI1/hSNF5 gene is involved (appears to account for over 80% of the cases). The correct diagnosis of the tumor is critical to any protocol. Studies have shown that 8% to over 50% of AT/RT tumors are diagnosed incorrectly.