Anaplastic oligodendroglioma involving the subcutaneous tissue of the scalp: Report of an exceptional case and review of the literature

Anaplastic oligodendroglioma [AO, World Health Organization (WHO) grade III] is an uncommon but aggressive tumor of the central nervous system that typically arises in adults. Clinically, patients present with seizures, and the prognosis is considered poor. Metastatic spread is extremely rare. We report an exceptional case of AO with extracranial scalp involvement, which arose in a patient with recurrent primary AO of the brain after chemoradiation, multiple cranial surgical resections, and subsequent scalp reconstruction. On histopathology, the subcutaneous tissue of the scalp contained several clusters and infiltrating cords of relatively small, epithelioid cells with hyperchromatic nuclei, scant eosinophilic cytoplasm, and perinuclear halos, which gave the cells a characteristic fried-egg appearance. By immunohistochemistry, the lesional cells were positive for glial fibrillary acidic protein and S-100. It is likely that surgical implantation and direct extracranial extension after craniotomy were the mechanisms responsible for dissemination of the patient's tumor.