This condition is usually associated with osteomyelitis in a cranial bone and originates from an infection in the ear or paranasal sinuses, or it is from a surgical procedure, particularly if the frontal sinus or mastoid had been opened or a foreign device inserted. Rarely, the infection is from a remote source or spreads outward from a dural sinus thrombophlebitis. Pus and granulation tissue accumulate on the outer surface of the dura, separating it from the cranial bone.
The symptoms are those of a local inflammatory process: frontal or auricular pain, purulent discharge from sinuses or ear, and fever and local tenderness. Sometimes the neck is slightly stiff. Localizing neurologic signs are usually absent. Rarely, a focal seizure may occur, or the fifth and sixth cranial nerves may be involved with infections of the petrous part of the temporal bone. The CSF is usually clear and under normal pressure but may contain a few lymphocytes and neutrophils (20 to 100 per mL; fewer than in subdural empyema) and a slightly increased amount of protein.
Treatment consists of antibiotics, usually vancomycin and cephalosporin, aimed at the appropriate pathogen(s)—often S. aureus. Later, the diseased bone in the frontal sinus or the mastoid, from which the extradural infection had arisen, may have to be removed. Results of treatment are usually good.
(See Chap. 42)
These types of abscesses possess unique clinical features and constitute important neurologic and neurosurgical emergencies. They are discussed in Chap. 42 with other diseases of the spinal column and spinal cord.
INTRACRANIAL SEPTIC THROMBOPHLEBITIS (SEE ALSO CHAP. 33)
The dural sinuses drain blood from all of the brain into the jugular veins. The largest and most important of these, and the ones usually involved by infection, are the lateral (transverse), cavernous, petrous, and, less frequently, the longitudinal (sagittal) sinuses. A complex system of lesser sinuses and cerebral veins connects these large sinuses to one another as well as to the diploic and meningeal veins and veins of the face and scalp. The basilar venous sinuses are contiguous to several of the paranasal sinuses and mastoid cells.
Usually there is evidence that septic thrombophlebitis of the large dural sinuses has extended from an infection of the middle ear and mastoid cells, the paranasal sinuses, or skin around the upper lip, nose, and eyes. Other forms of intracranial infection frequently complicate these cases, including meningitis, epidural abscess, subdural empyema, and brain abscess. Occasionally, infection may be introduced by direct trauma to large veins or dural sinuses. A variety of organisms, including all the ones that ordinarily inhabit the paranasal sinuses and skin of the nose and face, may give rise to intracranial thrombophlebitis. Streptococci and staphylococci are the ones most often incriminated. With the exception of fever and poorer outcome, the syndromes associated with septic phlebitis discussed below are similar to those produced by noninfectious thrombosis of the veins, as discussed in Chap. 33, on cerebrovascular diseases. Some of the subtle differences between syndromes involving each of the major venous sinuses are detailed in the following text.