As the abducens nerve passes near the apex of the petrous bone it is in close relation to the trigeminal nerve. Both may be implicated by inflammatory or infectious lesions of the petrous (apex petrositis), manifest by facial pain and diplopia (Gradenigo syndrome). Among the causes of this syndrome is osteomyelitis of the petrous bone. Fractures at the base of the skull and petroclival tumors may have a similar effect, and sometimes head injury alone is the only assignable cause. Occasionally, the sixth nerve is compressed by a congenitally persistent trigeminal artery. A congenital form of bilateral abducens palsy is associated with bilateral facial paralysis (Mobius syndrome) as discussed in Chap. 38. Patients with the Duane retraction syndrome type 1 (absent sixth nerve) have limited abduction and on adduction show characteristic retraction of the globe because of co-contraction of the medial rectus and lateral rectus muscles.
Cavernous Sinus Syndrome, Tolosa-Hunt syndrome, and Orbital Pseudotumor
Some of the diseases discussed previously are associated with a degree of pain, often over the site of an affected nerve or muscle or in the immediately surrounding area. But the development over days or longer of a painful unilateral ophthalmoplegia should raise suspicion for other conditions such as aneurysm, tumor, or inflammatory and granulomatous process in the anterior portion of the cavernous sinus or the adjacent superior orbital fissure (Table 13-4). In the cavernous sinus syndrome, involvement of the ocular motor nerves on one or both sides is accompanied by periorbital pain and chemosis (Fig. 13-5B). In a series of 151 such cases reported by Keane, the third nerve (typically with pupillary abnormalities) and sixth nerve were affected in almost all and the fourth nerve in one-third; complete ophthalmoplegia, usually unilateral, was present in 28 percent. Sensory loss in the distribution of the ophthalmic division of the trigeminal nerve was often added, a finding that is helpful in the differentiation of cavernous sinus disease from other causes of orbital edema and ocular muscle weakness.
Trauma and neoplastic invasion are the most frequent causes of the cavernous sinus syndrome. Thrombophlebitis, intracavernous carotid aneurysm or fistula, fungal infection, meningioma, and pituitary tumor or hemorrhage account for a smaller proportion (see “Septic Cavernous Sinus Thrombophlebitis” and “Cavernous Sinus Thrombosis” in Chaps. 12 and 33). A dural arteriovenous fistula is another rare cause.
The idiopathic granulomatous painful condition of the cavernous sinus has been termed Tolosa-Hunt syndrome; a similar process affecting structures of the orbit is known as orbital pseudotumor. Orbital pseudotumor causes an inflammatory enlargement of the extraocular muscles, which often also encompasses the globe and other orbital contents (Fig. 13-8). It is often accompanied by injection of the conjunctiva and lid and slight proptosis. One or more muscles may be involved and there is a tendency to relapse and later to involve the opposite globe. Visual loss from compression of the optic nerve is a rare complication. Associations with connective tissue disease have been reported and IgG4-related sclerosis has increasingly been identified as a cause. Ultrasonography examination or CT scans of the orbit show enlargement of the orbital muscles including the tendons, as opposed to thyroid ophthalmopathy in which the muscles are enlarged but the muscle tendons are typically spared.