Intracranial cellular schwannomas: a clinicopathological study of 20 cases.

Abstract

Cellular schwannoma is a specific subtype of schwannoma, prone to misinterpretation as a malignant neoplasm. Involvement of the intracranial compartment by these tumours is extremely rare. We aim to characterise this clinicopathological subgroup. We identified a total of 20 cellular schwannomas with predominant intracranial involvement. The mean age of the patients at the time of surgery was 37years (range=16-81), with a slight female predominance (1.5:1 ratio). The most common sites were the eighth (n=8) and fifth (n=6) cranial nerves. Three tumours involved the anterior cranial fossa/olfactory groove, and a single case involved the glossopharyngeal nerve. All tumours met established criteria for cellular schwannoma, and were composed of interlacing fascicles of spindle cells lacking Verocay bodies with minimal Antoni B pattern and variable chronic inflammation and foamy histiocytes. Rare findings included haemosiderin deposition (n=6), necrosis (n=4), brisk mitotic activity (>10 mitoses per 10 high-power fields) (n=2), focal epithelioid morphology (n=2), myxoid areas (n=2), neuroblastoma-like pattern (n=1) and granular cells (n=1). Immunohistochemical stains demonstrated expression of Schwann cell markers (S100 protein, SOX10, collagen IV) and preserved H3 K27 trimethylation in all cases tested. Fourteen patients had postoperative follow-up, ranging from 2months to 21years (mean=66months). In patients with follow-up, local recurrence/persistence developed in six cases; five tumours were initially incompletely resected. No metastatic disease or deaths were reported. Intracranial cellular schwannomas share morphological and immunophenotypical features with cellular schwannomas at others sites may demonstrate locally aggressive growth but appear to lack metastatic potential.