Mesothelioma is known for its diverse growth patterns. In addition to the more common subtypes – several rare variants of the disease are known.

Small cell mesothelioma

The small cell variant of mesothelioma is rare and can be misdiagnosed as a small cell carcinoma. Desmoplastic mesothelioma should present at least a fifty percent ‘small cell’ morphology to qualify as a rare variant of mesothelioma. Small cell mesothelioma does not display the haematoxphilic nucleoprotein precipitates – commonly seen in small cell carcinoma.

Lymphohistiocytoid mesothelioma

This is an extremely rare variant of mesothelioma and only counts for one percent of cases, and was first reported in 1988. Lymphohistiocytoid mesotheliomas are predominantly ‘sarcomatoid’ or poorly differentiated ‘epitheloid’ tumours. These rare mesotheliomas can also be characterised by histiocytoid neoplastic cells – obscured by intense lymphocytic infiltration.

Deciduoid mesothelioma

Only 3 cases have been reported – 2 patients were described by ‘ Nascimento et al’.  These epithelioid mesotheliomas were found in the peritoneum in young women. The tumour cells were large with abundant glassy eosinophilic cytoplasm, reminiscent of decidual cells and followed an aggressive course. The 3^rd reported case described by ‘Orosz et al’ was deciduoid mesothelioma of the peritoneum found in a 15 year old girl, she died 11 months later.

Desmoplastic small round cell tumour

Desmoplastic small round cell tumours (DSRCTS) have distinctive pathological features that differ from mesothelioma. Although DSRCTS is not generally considered to be a variant of mesothelioma – it may represent a primitive form of mesothelioma or ‘mesothelioblastoma’.

Well – differentiated papillary mesothelioma

Well-differentiated papillary mesothelioma is a rare variant of ‘epithelial mesothelioma’ and is thought to present low malignant potential. Most reported cases of papillary mesothelioma developed in the peritoneum of young women where a history of asbestos exposure was not always apparent. The tumours present as ‘peritoneal nodules’ and rarely occur in the pleura. 

Benign multicystic mesothelioma

Benign multicystic mesothelioma  – also referred to as (peritoneal inclusion cyst) is a rare lesion found on the abdominal peritoneal surface, and is predominantly found in pre-menopausal women. It may form a large multicystic mass; and although benign, its existence can cause infertility.

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