Granulomatous tissue response in germinoma, a diagnostic pitfall in endoscopic biopsy

We report a case of a 24-year-old man with a right thalamic germinoma that initially mimicked a granulomatous inflammation, compatible with neurosarcoidosis based on clinical symptoms, imaging results and histology of an endoscopically navigated biopsy. A second biopsy, prompted by clinical course, and performed openly from parieto-lateral revealed the underlying germinoma, obscured in the first biopsy by a granulomatous tissue response, particularly at the tumor edge. The present case highlights granulomatous inflammatory tissue response on the tumor edge of germinoma as a tumor-immanent diagnostic challenge. This diagnostic problem is aggravated by stereotactic and endoscopic approaches. We conclude that granulomatous inflammation in a specimen obtained by biopsy of a midline lesion should always be considered for the differential diagnosis of germinoma. Stereotactic and endoscopic surgery should sample several different target points within the lesion. Because of tumor heterogeneity of germinoma, the open biopsy approach is advantageous compared to endoscopic or stereotactic techniques for germinoma and should be considered if a germinoma is in the differential diagnosis and if allowed by the clinical situation.