Incidence of Subdural Hygroma on Routine Early Postoperative Imaging Following Foramen Magnum Decompression for Chiari Malformation Type 1 in 156 Patients

Abstract

To determine the incidence of subdural hygroma(SDH) on routine early post-operative imaging following foramen magnum decompression(FMD) with dural opening in patients with Chiari 1 malformation (CM1). Clinical and radiological data of 156 consecutive patients with CM1 who underwent FMD (2006-2023) were retrospectively analysed. Computed tomography (CT) scans done on the 7th postoperative day or earlier were reviewed for the presence of SDH (infra-and supratentorial) and ventriculomegaly. There were 96 (61.5%) males. The median age was 29.1 years. 64/156 (41 %) patients had SDH on postoperative CT done at median interval of 7 days (IQR, 5.8-7 days) after surgery. 22/64 (34.4%) patients were symptomatic for SDH, the main symptoms being holocranial headache (n=16), CSF leak (n=5) and acute respiratory distress (n=3). There was significant association between development of ventriculomegaly or worsening of preexisting ventriculomegaly and presence of SDH (p=0.004). The associated ventriculomegaly, present in 7/22 patients with symptomatic SDH, was managed with external ventricular drainage (EVD)(n=2), ventriculoperitoneal shunt (n=3) or widening of FMD and EVD (1)/ventriculo peritoneal shunt (1) (n=2). Two patients with SDH and ventriculomegaly died and 2 were moribund at 3 months after surgery. At median follow up of 12 months, the other 18 patients with symptomatic SDH had symptom resolution. SDH is a common finding in the early post-operative scans of patients undergoing FMD and dural opening for CM1. While nearly two-thirds of these patients are asymptomatic, SDH with ventriculomegaly can be associated with mortality and significant morbidity and may require emergency treatment.