BACKGROUND: Incidental skull lesions are increasingly detected due to the widespread use of brain imaging. We have encountered an unusual cohort of unclassifiable calvarial spindle cell lesions showing phenotypic overlap with perineurioma and meningioma, which we sought to further characterize. MATERIAL AND METHODS: Cases of unclassifiable low-grade spindle cell lesions arising in the calvarium were collected. Clinical, radiological and pathological findings were reviewed. All cases were uniformly stained for a panel of meningothelial and perineurial immunomarkers. RESULTS: Eight cases were identified (6 females, 2 males; 51-81 years), arising in the parietal (n = 4), frontal (n = 3), parietal-occipital (n = 1) bones. Radiologically, the lesions appeared as lytic with non-aggressive features, but progressive enlargement was documented in cases with serial imaging. Histologically, all cases were composed of uniform, bland spindle cells with elongated, tapered cytoplasm and inconspicuous nuclei arranged in short fascicles and whorls. Immunohistochemically, all cases were positive for EMA (8/8) and Collagen IV (3/3). The lesions showed consistent but limited staining for SSTR2a (2 cases, 6%-50%; 4 cases, 1%-5%). The lesional spindle cells were negative for PR (0/7), GLUT1 (0/6), S100 (0/6), CD34 (0/5), SOX10 (0/4) and claudin 1 (0/3). Follow-up (available in 6 patients; range 6-61 months, median 15.5 months) showed no evidence of recurrence after curettage or excision. CONCLUSION: Perineurioma-like, EMA-positive calvarial neoplasms are a rare group of spindle cell tumours for which no local recurrence or distant metastasis has been documented to date, although they do show a propensity for progressive growth. Recognition of their distinctive clinicopathological and radiological features is important for accurate diagnostic classification and appropriate patient management.
Rizwan et al. (2026) studied this question.