 
Graves’disease is an
auto-immune affection which involves the thyroid and the orbit in both
hyper and enthyroid patients. Thyroid orbitopathy is responsable of 80
% of bilateral exophthalmos and is far more frequent in women. Orbital
fat and lacrymal gland are enlarged but the involvement predominates on
the extraocular muscles (fig. 14) : the inferior and medial recti being
the earliest and the most commonly involved with a typical
spindle-shaped enlargement. Optic neuropathy due to compression of the
optic nerve at the orbital apex can be evaluated by 3D CT reformations
as well as by MR imaging (fig. 14) and can be treated by orbital
decompression (ref. 8).
Pseudotumor, a non granulomatous
inflammatory process, composed of mature lymphocytes and with no known
etiology account for 4,7 to 6,3 % of all orbital disorders. They can
involve various anatomic components of the orbit and so periscleritis
(fig. 8), perineuritis (fig. 17), dacryadenitis, myositis (fig. 15) and
trochleitis (fig. 16) have been described (ref. 9). Fatty infiltration
as well as multiple locations are frequently found. The involvement of
the orbital apex results in Tolosa-Hunt syndrome (ref. 10) if the
superior orbital fissure and cavernous sinus are affected (fig. 17).
CT and MR imaging of myositis show
enlargement of one or several muscles including respective tendons
(fig. 15). Diagnosis is based on clinical symptoms (sudden onset of
diplopia, pain, redness), radiological findings and evolutive response
to steroid therapy in most acute cases but recurrences are frequent.
Biopsy is needed only in a few patients. The chronic form (sclerosis
pseudotumor) is not affected by steroid therapy (ref. 11). In childhood
orbital pseudotumor may mimic rhadomyosarcoma and in adulthood,
the main differential diagnosis are lymphomas or leukemia.
Hematogenous metastases from primary
tumors in the breast, lung, prostate or kidney can reach the orbit and
affect the extraocular muscles, the orbital fat and the periorbital
space with or without bone involvement (fig. 18). A particular form of
metastases associated with scirrous carcinoma of breast and responsable
for diffuse orbital infiltration with enophthalmos may mimic a diffuse
pseudotumor (ref. 10).
Plexiform neurofibroma associated
with type 1 neurofibromatosis , more infiltrative than solitary
neurofibroma, extends into the orbital fat, around the extraocular
muscles, in the eyelids in the distribution of the V1 nerve and may be
associated with a dysplasic orbit (fig. 19).
Wegener’s granulomatosis, a
necrotizing granulomatous inflammation affecting primarily the lungs
and the kidneys may involve the orbital apex bilaterally. The diagnosis
is based on serologic or pathologic findings (ref. 10).
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