Delayed intraparenchymal pneumocephalus causing internal capsule injury after endoscopic transsphenoidal surgery for recurrent Rathke’s cleft cyst: illustrative case

BACKGROUND: Pneumocephalus is a rare but serious complication after endoscopic transsphenoidal surgery (ETSS), usually associated with CSF leakage and occasionally progressing to tension pneumocephalus. Delayed intraparenchymal pneumocephalus causing focal brain injury after ETSS for recurrent Rathke's cleft cyst (RCC) is exceptionally rare. OBSERVATIONS: A 74-year-old woman underwent ETSS for recurrent RCC and was discharged on postoperative day (POD) 10 after an uneventful early course. On POD 37, she developed sudden left hemiparesis and mild dysarthria. Head CT demonstrated pneumocephalus extending from the sella toward the right internal capsule without rhinorrhea. With conservative management, the pneumocephalus gradually resolved, revealing parenchymal injury involving the posterior limb of the right internal capsule on CT and MRI. She later reported repeated nose blowing after discharge, including on the morning of symptom onset. Intraoperative endoscopic review revealed a depression in the anterior perforated substance, anatomically corresponding to the ruptured RCC and subsequent injury site. LESSONS: In recurrent or ruptured RCCs, occult communication between the sellar region and adjacent brain may permit air entry after postoperative Valsalva maneuvers. Strict counseling, recognition of high-risk parenchymal findings, and airtight multilayer reconstruction with a vascularized mucosal flap may reduce this risk. https://thejns.org/doi/10.3171/CASE26647.