Unilateral mastoid hypertrophy.

A 34-year-old man lacerated his forehead and was brought to the emergency room. Skull films (fig s. 1 A and 1 B) showed small and large rad iolucent , air-containing ce lls extending from the upper posterior reg ion of the mastoid area on the left side, across th e temporal-occipital suture into th e squamous portion of the occipital bone, and into the posterior part of the parietal bone. The septa of the numerous air ce lls were delicate and showed no evidence of thickening. The cells measured 230 mm . Th e mastoid air ce lls on the opposite (right) side were well developed, of normal size, and showed no extension beyond the temporal bone. The patient 's history was completely negative and the physical examination was negati ve. Computed tomography (CT) (figs. 1 C and 1 D) showed external symmetry of the skull. It showed that the excessive air-cell development caused inward displacement of the inner table of th e sku ll wi th encroachment of th e upper posterior fossa and supratentorial region of th e left posterior calvaria. The lumen of th e air cell s contained gas with a CT attenuation value of 1,000 Hounsfield units (H) . The inward displacement of the left occ ipital lobe area caused 1.0 mm of displacement of the pineal gland to the right of th e midline . Th ere was no displacement or deform ity of the ven tricular system of th e brain , but the quadrigeminal c istern (cistern of Galen ) had minimal flattening of its left lateral border. The d iploic space between th e internal and external tables of the skull was widest in the occipital squamous region where it measured 20 mm . The patien t remained well during a year of fo llow-up.