ORBITAL INFLAMMATORY PSEUDOTUMOR

Signs and Symptoms

Chemosis and proptosis in orbital inflammatory pseudotumor.

There is no racial or gender predilection with orbital inflammatory pseudotumor (OIP) and patients may range from 4 to 80 years.¹ While chronic forms do exist, the typical presentation includes acute onset of orbital pain, swelling, chemosis and proptosis.² There may be significant injection overlying muscle insertions. There may be a palpable mass, and there is often ophthalmoplegia and diplopia. There may be associated vision loss with concurrent disc edema or optic atrophy secondary to nerve compression. The disease is typically unilateral and may be recurrent. However, this condition may be commonly bilateral in children. The term is used to describe any idiopathic inflammatory lesion that simulates a neoplasm within the orbit. It presents with compressive effects to orbital structures with evidence of inflammation and infiltration. It is believed to be a self-limiting disease and, while benign in nature, can cause serious ocular damage and possibly vision loss from optic nerve compression.

Pathophysiology

Orbital inflammatory pseudotumor can be subdivided into different types: granulomatous, sclerosing, vasculitic and eosinophilic, depending upon the histological characteristics.³ Granulomatous orbital pseudotumor is characterized by histiocytes and multinucleate giant cells. Sclerosing orbital pseudotumor presents with minimal inflammatory infiltrate with a greater degree of interstitial connective tissue. Vasculitic inflammatory pseudotumor involves primary vasculitis of small vessels with lymphocytes and granulocytes destroying the muscularis and elastic lamina of the vessels. Eosinophilic pseudotumor involves tissue eosinophilia without vasculitis.

Mechanisms ranging from autoimmunity to infectious to poor wound healing have all been proposed to account for the development of orbital inflammatory pseudotumor. The end effect is an inflammatory infiltrate occupying space and compressing tissues, vessels and nerves with a mass-lesion effect similar to a true tumor.

There are strong similarities between OIP and the Tolosa-Hunt syndrome of painful ophthalmoplegia. Diagnostic neuro-radiological testing of these two diseases shows identical signal intensity, albeit in different locations. Orbital inflammatory pseudotumor is typically orbital and Tolosa-Hunt syndrome is predominately retro-orbital, specifically localizing to the anterior cavernous sinus. This, in combination with nearly identical clinical presentations and histopathologic findings makes the two diseases nearly indistinguishable. Some have theorized that they are on the continuum of the same condition.⁴

Management

The diagnosis of OIP is usually a clinical one. Contrast-enhanced MRI with multiple coronal views and fat saturation is recommended. Lesions will be hypointense to orbital fat on T₁-weighted images and isointense or minimally hyperintense to fat on T₂-weighted images. High-resolution CT scan will demonstrate soft tissue swelling, but this is not the diagnostic modality of choice.⁵

Oral corticosteroids are the recommended treatment for OIP. This condition is extremely steroid-responsive and was, at one time, considered a diagnostic finding. Oral prednisone 60mg to 80mg qd with rapid tapering upon clinical improvement is acceptable therapy.⁵ Improvement typically occurs within 48 hours of steroid initiation. It must be cautioned, however, that malignant disease may also show a transient response to steroid treatment. Abrupt recurrence upon discontinuation of steroids is not characteristic of OIP and, therefore, less benign processes should be sought out. Radiation therapy may work in those who are not steroid responsive or can be used adjunctively. Other immunosuppressant agents have achieved some anecdotal success.

Clinical Pearls

• Consider OIP in cases of painful ophthalmoplegia.
• The differential diagnosis includes orbital cellulitis, thyroid ophthalmopathy, sarcoidosis, lymphoid tumor, lymphangioma and metastatic carcinoma.
• In that this is a diagnosis of exclusion, malignant disease must first be aggressively ruled out.
• Due to potential damage to orbital structures, biopsy typically is not indicated.

Other reports in this section

• Traumatic Optic Neuropathy
• Orbital Inflammatory Pseudotumor
• Brown's Syndrome
• Pseudotumor Cerebri