Subdural tension pneumocephalus following surgery.

A clinical computed tomographic (CT) study of six patients, two with tension and four with benign postoperative subdural pneumocephalus, was done coupled with a data analysis of the literature. The mass effect of a tension subdural pneumatoma was demonstrable as shift in the midline structures when the air was unilateral, whereas an asymptomatic pneumocephalus showed no actual mass effect. Inspection of the digital lateral scout view studies usually provides a rough estimate of the magnitude of a pneumatoma; the volume of the air could be computed on the axial transverse CT scans. In a preliminary in vivo volume estimation, the subdural air measured more than 65 cm3 for the two symptomatic patients and less than 20 cm3 for the asymptomatic ones. Of 21 reported cases of postsurgical tension pneumocephalus, 18 (86%) had the pneumatoma in the subdural space. The predisposing neurosurgical conditions to tension pneumatoma included: (a) a preexisting open cerebrospinal fluid drainage device; (b) surgery on the posterior fossa in the sitting position; and (c) chronic subdural hematoma.