Refractory Bacterial Meningitis Associated with an Occult Posterior Fossa Dermal Sinus Tract in an Infant: A Case Report.

Posterior fossa dermal sinus tracts are extremely rare congenital lesions that may extend intracranially and communicate with the dura or brain tissue. This abnormal connection can provide a persistent route for bacterial entry into the central nervous system, predisposing patients to severe infections such as meningitis. We report the case of a 1-year-old boy with refractory bacterial meningitis that remained unresponsive to prolonged broad-spectrum antibiotic treatment. MRI revealed an occult posterior fossa lesion, and cerebrospinal fluid NGS detected multiple microorganisms of uncertain clinical significance, none of which was considered the definitive causative pathogen. Intraoperatively, a sinus tract was found communicating with an intracranial cystic lesion, subsequently confirmed as an infected dermoid cyst on histopathology. After surgical excision and postoperative intraventricular antimicrobial therapy, the patient showed sustained improvement with no recurrence at 6-month follow-up. This case suggests that an occult posterior fossa dermal sinus tract may represent an underrecognized anatomical source of treatment-resistant meningitis and highlights the importance of early structural evaluation when standard antimicrobial therapy fails. Timely surgical intervention may be important for source control and prevention of recurrence.