Factors determining hydrocephalus after decompressive craniectomy: the role of interhemispheric hygroma

Post-traumatic hydrocephalus (PTH) is a recognized complication following decompressive craniectomy (DC) in patients with traumatic brain injury (TBI). Reported risk factors remain inconsistent across studies. Interhemispheric subdural hygroma has been suggested as a potential radiological marker, although its quantitative relevance has not been clearly established. This study aimed to evaluate the association between interhemispheric hygroma and hydrocephalus after DC and to explore whether hygroma thickness may help identify patients at higher risk of treatment requirement.

We conducted a retrospective observational study at a Level I trauma center including patients older than 15 years who underwent DC for TBI between 2011 and 2025. Radiological hydrocephalus was defined using a modified frontal horn index >33% combined with Gudeman CT criteria. Clinical, surgical, and radiological variables were analyzed. Multivariable logistic regression was used to identify independent associations. The discriminative performance of interhemispheric hygroma thickness for predicting hydrocephalus requiring treatment was assessed using receiver operating characteristic (ROC) curve analysis, and the optimal threshold was determined using the Youden index.

A total of 104 patients were included; 52 (50%) developed radiological hydrocephalus. The median follow-up of the cohort was 13.9 months (IQR 3.8-31.1). Follow-up duration differed significantly between patients with and without radiological hydrocephalus (21 vs. 12.3 months; p = 0.013), and between treated and non-treated hydrocephalus (32 vs. 12.4 months; p < 0.001). Interhemispheric hygroma thickness was greater in patients with hydrocephalus and remained independently associated in multivariable analysis (OR 1.19 per mm; 95% CI 1.03-1.39). In the subgroup with treated hydrocephalus, hygroma thickness also remained independently associated with treatment requirement (OR 1.30 per mm; 95% CI 1.01-1.67). ROC analysis showed good discriminative performance (AUC 0.81).

A threshold of approximately 8 mm demonstrated high sensitivity with acceptable specificity for predicting treatment. Interhemispheric hygroma thickness was independently associated with post-traumatic hydrocephalus after DC and with subsequent treatment requirement. These findings suggest that hygroma thickness may represent a useful radiological parameter for postoperative monitoring, although external validation is warranted.