Pneumocephalus and delayed hydrocephalus following endoscopic endonasal biopsy of skull base lesion: diagnostic pitfalls and the role of immunohistochemistry.

The endoscopic endonasal approach (EEA) has been increasingly utilized for interventions involving the middle cranial base because of its close anatomical relationship with the nasal cavity and nasopharynx. This technique is widely applied in neurosurgical and otorhinolaryngological practice for the management of pituitary lesions, sellar and parasellar pathologies, sphenoid sinus tumors, cavernous sinus lesions, and tumors of the nasal cavity and nasopharynx, offering improved surgical access and patient comfort. Endoscopic procedures may be associated with serious complications, including intracranial hemorrhage, pneumocephalus, cerebrospinal fluid (CSF) leakage, infection, and cranial nerve injury, which can occur in both early and late postoperative periods. We report a patient who developed early postoperative pneumocephalus, intracerebral hemorrhage, and CSF leakage following endoscopic endonasal biopsy of a lesion adjacent to the mid-cranial base. Based on clinical and radiological findings, the lesion was initially suspected to represent nasopharyngeal carcinoma. Therefore, the patient underwent an endoscopic endonasal biopsy rather than gross total resection. Histopathological and immunohistochemical analyses subsequently established the diagnosis of meningioma. Two weeks postoperatively, the patient developed CSF leakage, pneumocephalus, and intracerebral hemorrhage, and the skull base defect was repaired via an EEA. Subsequently, the patient developed hydrocephalus in the mid-to-late postoperative period, which was successfully treated with ventriculoperitoneal shunt placement, resulting in complete clinical recovery. This case highlights the need for close clinical and radiological follow-up not only in the early period but also in the mid-to-late postoperative periods. Furthermore, radiological findings suggestive of malignancy may be inconsistent with immunohistochemical results; this underscores the critical role of immunohistochemical examination in determining definitive diagnosis and prognosis.