Contributor: Gordon K. Klintworth
The imprecise term pseudotumor is well entrenched in the literature despite its shortcomings. In the orbit the designation refers to an idiopathic inflammatory process that often involves the extraocular muscles, the adjacent adipose tissue, and sometimes the lacrimal gland. An idiopathic orbital inflammatory pseudotumor is a diagnosis of exclusion, both clinically and histopathologically.
Numerous histopathologiv variants of the orbital tumor exist. A lipogranulomatous reaction may represent orbital fat necrosis. Another variant of the inflammatory pseudotumor is characterized by proliferating fibroblasts in a collagenous or myxomatous stroma reminiscent of nodular fasciitis. Vascularity is prominent, but the inflammatory cell infiltrate is scant and mitotic activity is inconspicuous. Foci of dense connective tissue without a significant inflammatory cell infiltrate characterize yet another type of orbital pseudo-tumor. An idiopathic granulomatous orbital inflammation, which has designated "sarcoidosis limited to the orbit" is related to other types of inflammatory orbital pseudotumor rather than sarcoidosis. An orbital inflammatory pseudotumor typically consists of a mixed inflammatory cell infiltrate of lymphocytes, plasma cells, eosinophils and occasionally epithelioid cells. Lymphoid follicles and germinal centers are found in some cases, and varying degrees of fibrosis are usually present. Extensive sclerosis often characterizes chronic lesions. Some inflammatory pseudotumors are composed predominantly of lymphocytes. Many inflammatory pseudotumors are composed predominantly of lymphocytes (lymphoid pseudotumor); others consist of a cytologically benign mononuclear inflammatory infiltrate composed of lymphocytes, plasma cells, macrophages, and rare eosinophils.
Inflammatory pseudotumor is a common cause of proptosis and partial immobility of the eyeball. The lesion is frequently biopsied. Patients with orbital inflammatory pseudotumors often develop ocular pain, proptosis, and decreased ocular motility. The diagnosis of orbital pseudotumor can only be mage histopathologically after excludin all known causes of orbital inflammatio
Pathogens, such as bacteria and fungi, need to be ruled out. Other lesions from which an orbital pseudotumor needs to be differentiated include various types of lymphoid tumor (reactive lymphoid hyperplasia [lymphoid hyperplasia - reactive, lymphoma, atypical lymphoid hyperplasia, mycosis fungoides, Waldenström macroglobulinemia, Burkitt lymphoma], systemic vasculitides (such a polyarteritis nodosa), limited Wegener granulomatosis [Wegener granulomatosis - limited], systemic Wegener granulomatosis [Wegener granulomatosis - systemic], various inflammatory diseases [sarcoidosis, Kimura disease, midline lethal granuloma,necrobiotic xanthogranuloma , Erdheim-Chester disease, Rosai-Dorfman disease], multiple myeloma, lymphoplasmacytoid tumor, inflammatory reactions around other lesions (such as a pleomorphic adenoma of the lacrimal gland or ruptured dermoid cyst).
Because biopsies provide a limited amount of material for histopathologic evaluation inflammatory reactions around other lesions such as a pleomorphic adenoma of the lacrimal gland or ruptured dermoid cyst may be mistaken for an inflammatory pseudotumor.