Pneumocephalus after posterior fossa surgery in the lounging position: risk analysis of intracranial air collections and clinical outcome by voxel-based volumetry.
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OBJECTIVE: Semisitting or lounging patient positions offer several advantages in neurosurgical procedures, particularly for the resection of large and highly vascularized posterior fossa lesions. However, concerns persist regarding potentially severe complications such as tension pneumocephalus (TP) and venous air embolisms. The aim of this study was to assess the extent and distribution of postoperative pneumocephalus and to identify risk factors of TP. METHODS: This retrospective analysis included consecutive patients who underwent posterior fossa surgery in the lounging position from January 2010 to November 2020 at a single center. Postoperative cranial CT scans acquired within 24 hours after surgery were registered and normalized to the common Montreal Neurological Institute space to measure intraventricular, subdural, and total intracranial air using voxel-based volumetry. TP was defined as intracranial air associated with reduced consciousness, and its treatment was typically performed via external ventricular drain (EVD) placement or subdural air exchange through mini burr hole trepanation. Patient characteristics, surgical details, and clinical outcome were evaluated. RESULTS: Overall, 836 patients (462 female, mean age 48.7 years) were included. The indication for surgery was resection of a posterior fossa tumor (96.1%, n = 803), vascular pathology (2.6%, n = 22), malformation (1.1%, n = 9), or other pathology (0.2%, n = 2). Lateral suboccipital and midline suboccipital approaches were performed in 93.8% (n = 784) and 6.2% (n = 52) of patients, respectively. Intracranial air was detected in all patients, with a mean volume of 74 ± 59 mL. The volumetric analysis revealed significantly higher mean volumes of intracranial air (midline: 94 ± 72 mL, lateral: 73 ± 58 mL) [t(828) = 2.44, p = 0.008 (95% CI 4-38)] and intraventricular air (midline: 29 ± 32 mL, lateral: 3 ± 14 mL) [t(828) = 11.36, p < 0.001 (95% 21-30)] in midline approaches compared with lateral approaches. TP occurred in 3.0% of patients, with higher rates (15.4%) in those who underwent midline craniotomies compared with lateral approaches (2.0%) [χ2(1) = 31.14, p < 0.001]. Patients with TP required longer ventilation, intensive care unit stays, and hospitalizations, although Karnofsky Performance Status scores did not differ significantly at follow-up. The logistic regression analysis identified surgical approach, age, duration of surgery, and sex as independent predictors of TP [χ2(4) = 41.34, p < 0.001]. The area under the curve (AUC) analysis indicated that intraventricular air volumes ≥ 27.6 mL were associated with EVD placement (AUC = 0.92, sensitivity = 0.90, specificity = 0.95). TP was managed effectively in all cases, with no long-term sequelae. CONCLUSIONS: These findings suggest that the lounging position can be performed safely with careful monitoring for TP, particularly in older male patients and those undergoing longer surgeries via midline approaches. Awareness of risk factors and early postoperative imaging can help mitigate complications and improve patient outcomes.