Nonspecific orbital inflammation (NSOI), also known as idiopathic orbital inflammation (IOI) or orbital pseudotumor, is an inflammatory condition that can affect the extraocular muscles, orbital fatty tissues, lacrimal gland, and sclera without any underlying condition. This disease is a diagnosis of exclusion as it can manifest as infections, neoplasms, or other systemic conditions.

NSOI is the third most common orbital inflammatory disease, followed by thyroid disease and lymphoproliferative disease. It can present unilaterally or bilaterally. Bilateral cases are more often seen in children. It can affect all ages and either sex, but there is a higher predominance in middle-aged patients and in female patients.

Patients will classically present with sudden-onset diffuse chemosis and orbital pain. They can also present with proptosis, diplopia, and visual changes. Rarely, NSOI can present as a focal mass or with optic nerve sheath swelling (perineuritis). CT / MRI and rarely orbital biopsy can aid in diagnosis. The treatment of choice is oral corticosteroids, but other options such as external beam radiotherapy, chemotherapeutic agents, or surgical decompression may be used.