Pseudotumor

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      Orbital pseudotumor is a non-specific inflammation of orbital tissues. It tends to be unilateral and accounts for 25% of all cases of unilateral exophthalmos. It can be remitting or chronic and progressive. It may spontaneously regress or respond to steroids. It involves predominantly the tissues immediately behind the globe. Endnote The scleral margin often appears thickened due to inflammatory edema of the sclera and fluid within Tenon's space. Pseudotumor is an infiltrative process and usually involves both the extraconal and intraconal spaces. It appears on CT scan as areas of soft tissue density with poorly defined margins.

      The earliest changes of pseudotumor may be subtle edema of the retrobulbar fat. MR imaging with fat suppression may be the most sensitive method for detecting these early changes. Orbital myositis refers to solitary involvement of one of the extraocular muscles, usually the inferior rectus. Sometimes, pseudotumor will appear as a discrete mass and simulate a neoplastic lesion. Lymphoma must be considered in these cases because benign pseudotumor may evolve to lymphoma. 

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