General Information
- Intracranial disease. Extension of intracranial tumors, usually frontal lobe or sphenoid wing meningiomas, may present with proptosis in addition to cranial neuropathy and decreased vision. Imaging, preferably with MRI, is indicated.
- Cavernous sinus arteriovenous fistula (AVF) (e.g., carotid–cavernous or dural sinus fistula): AVF is either spontaneous, indirect (usually in older patients, Barrow type B-D) or posttraumatic, direct (in younger patients, Barrow type A). A bruit is sometimes heard by the patient and may be detected if ocular auscultation is performed. Pulsating proptosis, arterialized “corkscrew” conjunctival vessels, increased IOP, retinal venous congestion, and chemosis may be present. May mimic an orbital disease, including TED and IOIS. In the early stages, often misdiagnosed as conjunctivitis, asymmetric glaucoma, etc. CT scan reveals enlarged superior ophthalmic vein(s), sometimes accompanied by enlarged extraocular muscles. An orbital color Doppler US shows reversed, arterialized flow in the superior ophthalmic vein(s). MRA or CTA may reveal AVF but a definitive diagnosis usually requires cerebral arteriography. Evidence of posterior cortical venous outflow on arteriography increases the risk of hemorrhagic stroke. Of note, posterior cortical venous outflow is more common in patients with bilateral orbital signs, but is seen in 10% of patients with unilateral presentation. Also remember that arteriography must be performed on both cerebral hemispheres and include the internal carotid, external carotid, and basilar arteries (“six vessel angio”). The cavernous sinuses are connected by the circular sinus and, on occasion, a carotid–cavernous fistula manifests clinically in the contralateral orbit.
- Septic cavernous sinus thrombosis: Orbital cellulitis signs, plus dilated and sluggish pupils as well as palsies of the third, fourth, fifth, and/or sixth cranial nerves out of proportion to the degree of orbital edema. Decreasing level of consciousness, nausea, vomiting, and fevers can occur. May be bilateral with rapid progression. See 7.3.1, ORBITAL CELLULITIS.
- Orbital vasculitis (e.g., GPA and polyarteritis nodosa): Systemic signs and symptoms of vasculitis (especially sinus, renal, pulmonary, and skin disease), fever, markedly increased ESR, and positive cANCA or pANCA. Of note, cANCA may be normal in two-third of patients with the limited sino-orbital variant of GPA.
- Varix: A large, dilated vein in the orbit that produces proptosis when it fills and dilates (e.g., during a Valsalva maneuver or with the head in a dependent position). When the vein is not engorged, the proptosis disappears. CT demonstrates the dilated vein if an enhanced scan is performed during a Valsalva maneuver. Calcification may be seen in long-standing lesions.
- Poorly understood processes:
- Tolosa–Hunt syndrome (THS): NOT equivalent to orbital apical IOIS. Histopathologically, a granulomatous inflammation of the orbital apex and/or carotid siphon within the cavernous sinus. Presents with acute pain, cranial neuropathy, and sometimes proptosis. A diagnosis of exclusion. Difficult to diagnose with CT. MRI shows isolated, ipsilateral enlargement of the cavernous sinus. Usually sensitive to corticosteroid therapy, but pain typically responds much more quickly than external ophthalmoplegia, which may take weeks to resolve. Because confirmatory biopsy is usually not feasible, every patient with presumed THS must be followed long-term, even after rapid response to corticosteroids, to rule out other etiologies. Repeat imaging is usually indicated several months after the initial event to rule out progression. Presumed THS recurs in about one-third of patients. Remember that other significant pathologies, including sarcoidosis, lymphoma, metastasis, and even aneurysm may show a temporary response to corticosteroids.
- Sclerosing orbital pseudotumor: Likely not a true orbital inflammation or a subtype of IOIS. May be a form of idiopathic multifocal sclerosis. Presents with chronic pain, external ophthalmoplegia, and possibly optic neuropathy. Diagnosis requires biopsy. Histopathology shows wide swaths of monotonous fibrous tissue interspersed with mild inflammation. Treatment is difficult and may necessitate antimetabolite therapy, debulking, and in severe cases, exenteration.
- Orbital amyloid: May be primary (isolated) or secondary to systemic disease. All patients require a systemic workup, including a cardiology consult to rule out cardiomyopathy. Diagnosis is made by judicious orbital biopsy (this lesion is highly vascular and hemostasis is often difficult to obtain). Treatment is highly variable.