Pneumocephalus: Presence of air or gas within the intracranial cavity (e.g., epidural space, subdural space, intracerebral, etc.) which may result from traumatic injuries, fistulous tract formation, erosions of the skull from NEOPLASMS or infection, NEUROSURGICAL PROCEDURES, and other conditions.Frontal Sinus: One of the paired, but seldom symmetrical, air spaces located between the inner and outer compact layers of the FRONTAL BONE in the forehead.Craniotomy: Any operation on the cranium or incision into the cranium. (Dorland, 28th ed)Cerebrospinal Fluid Rhinorrhea: Discharge of cerebrospinal fluid through the nose. Common etiologies include trauma, neoplasms, and prior surgery, although the condition may occur spontaneously. (Otolaryngol Head Neck Surg 1997 Apr;116(4):442-9)Maxillary Fractures: Fractures of the upper jaw.Fistula: Abnormal communication most commonly seen between two internal organs, or between an internal organ and the surface of the body.Osteoma: A benign tumor composed of bone tissue or a hard tumor of bonelike structure developing on a bone (homoplastic osteoma) or on other structures (heteroplastic osteoma). (From Dorland, 27th ed)Ventriculoperitoneal Shunt: Surgical creation of a communication between a cerebral ventricle and the peritoneum by means of a plastic tube to permit drainage of cerebrospinal fluid for relief of hydrocephalus. (From Dorland, 28th ed)Clostridium septicum: A species of gram-positive bacteria in the family Clostridiaceae. Infections have a strong association with malignancies and also with GAS GANGRENE.Sphenoid Sinusitis: Inflammation of the NASAL MUCOSA in the SPHENOID SINUS. Isolated sphenoid sinusitis is uncommon. It usually occurs in conjunction with other paranasal sinusitis.Sneezing: The sudden, forceful, involuntary expulsion of air from the NOSE and MOUTH caused by irritation to the MUCOUS MEMBRANES of the upper RESPIRATORY TRACT.Petrous Bone: The dense rock-like part of temporal bone that contains the INNER EAR. Petrous bone is located at the base of the skull. Sometimes it is combined with the MASTOID PROCESS and called petromastoid part of temporal bone.Subarachnoid Space: The space between the arachnoid membrane and PIA MATER, filled with CEREBROSPINAL FLUID. It contains large blood vessels that supply the BRAIN and SPINAL CORD.