Rhabdoid

In pathology, the term “rhabdoid” is used to describe tumour cells that resemble rhabdomyoblasts, which are immature skeletal muscle cells. However, these cells are not true rhabdomyoblasts and the tumours they arise in are not related to muscle tissue. Rhabdoid cells can be seen in a wide variety of tumour types and the presence of these cells in a tumour is generally associated with a poor prognosis.

Tumours containing rhabdoid cells

Rhabdoid cells can be found in a variety of tumours, including:

• Atypical teratoid/rhabdoid tumour (AT/RT): A very aggressive tumour usually occurring in the central nervous system (CNS) of young children.
• Rhabdoid tumour of the kidney: A rare and aggressive pediatric renal tumour.
• Malignant rhabdoid tumour (MRT): Originally described in the kidney but can occur in almost any part of the body, including the liver, skin, and soft tissues.
• Malignant peripheral nerve sheath tumour (MPNST): MPNST is a type of sarcoma that arises from cells in a nerve. MPNSTs that contain rhabdoid cells are described as Triton tumours.
• Rhabdoid features in other tumours: Including some carcinomas and sarcomas, where the presence of rhabdoid cells signifies a particularly aggressive course.

Microscopic appearance of rhabdoid cells

Under the microscope, rhabdoid cells are characterized by:

• Discohesive (single cells, not stuck together).
• Large, eccentric nuclei.
• Prominent nucleoli.
• Ample cytoplasm that is eosinophilic (pinkish with standard H&E staining).
• Inclusion-like cytoplasmic bodies, which are dense accumulations of intermediate filaments.

Markers for identifying rhabdoid cells

Immunohistochemical markers are used to help identify rhabdoid cells and can include:

• Muscle-specific markers (such as desmin and MyoD1): While rhabdoid tumours are not of muscular origin, checking for muscle-specific markers like desmin and MyoD1 can be important in the differential diagnosis. Desmin positivity is generally not expected in rhabdoid tumours but may be evaluated to differentiate rhabdoid features from those of true muscle-derived tumours or to rule out rhabdomyosarcoma, especially in pediatric cases.
• Loss of INI1/SMARCB1 expression: This is a hallmark feature of many rhabdoid tumours. The INI1 gene, also known as SMARCB1, is a tumour suppressor gene, and its loss is critical in the pathogenesis of rhabdoid tumours.
• Vimentin: Often positive in rhabdoid tumours, reflecting the mesenchymal origin of these cells.
• Epithelial markers (such as cytokeratins): May be positive in rhabdoid features within carcinomas.
• Epithelial membrane antigen (EMA): Can also show positivity in rhabdoid tumours.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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