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Neuroradiology Case of the Week
Case 391
March 2009
Sam McCabe, MD, and PL Westesson, MD, PhD, DDS
Clinical
Presentation: Patient is a 42-year-old male with right-sided orbital pain, increased with eye movement.
Imaging Findings: Non-contrast CT images depict a large, destructive mass centered in the right retrobulbar space. It demonstrates bony destruction and direct invasion of the right ethmoid and maxillary sinuses and nasal cavity.
MR images demonstrate a homogeneous lesion slightly hyperintense to skeletal muscle on T1 weighted images. It enhances avidly and engulfs the medial and inferior rectus muscles.
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| Figure 1: Axial non-contrast CT demonstrates a homogeneous soft tissue mass occupying the right orbital apex and extending into the adjacent ethmoid sinus. Destruction of the bony lamina papyracea is evident. |
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| Figure 2: Coronal reformatted CT image demonstrates invasion of the right maxillary sinus and nasal cavity by the mass. The optic nerve is not directly involved but is deviated superolaterally by the lesion. |
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| Figure 3: Axial post-contrast T1 MR image demonstrates enhancement of the thickened right paranasal mucosa as well as the anteromedial aspect of the lateral pterygoid muscle, suggesting infiltration by the orbital mass. |
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| Figure 4: Coronal T1-weighted MR demonstrates the extent of the homogenous destructive orbital lesion, which directly invades the ethmoid and maxillary sinus as well as the nasal cavity. |
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| Figure 5: Post-contrast coronal T1 MR image at the same level demonstrates intense enhancement of the mass. The medial and inferior rectus muscles cannot be clearly delineated. |
Diagnosis: Orbital pseudotumor (biopsy)
Discussion: Orbital pseudotumor is an idiopathic inflammatory condition of the orbit. Leading hypotheses as to its etiology include immune or autoimmune-related versus a low grade fibrosarcoma with lymphomatous (inflammatory) cells. Because it is not associated with known underlying vasculitis, neoplasm, infection, or systemic inflammatory condition, pseudotumor is a diagnosis of exclusion. Typically this entity will present with orbital pain and restricted eye movements. Uveitis, scleroretinitis, proptosis, and even retinal detachment can also be seen. Peak incidence is around 45 years of age. There is no sex predilection. OP is bilateral in up to 25% of cases. Treatment with steroids is usually effective. Radiation therapy is used for unresponsive or refractory cases. Tolosa Hunt syndrome is an etiologically related condition of intracranial pseudotumors with similar imaging and histopathological characteristics.
Imaging depicts a focal or diffuse enhancing soft tissue mass within the orbit. It may demonstrate infiltrative features with poorly defined margins and extension into adjacent tissue compartments, such as in our case. Alternatively, the mass may be confined to a region within the orbit and lack aggressive features. Subcategories including myositic, lacrimal, apical, anterior and diffuse are based both on the location and extent of disease. The myositic and lacrimal forms are the most common. The myositic form may involve any of the extraocular muscles without preference. Multiple muscles are involved in 50%. A key point is that the inflammation does not spare the tendon, allowing this entity to be distinguished from Graves opthalmopathy, which spares the muscle tendon and has a typical pattern of muscular involvement (inferior rectus first). The lacrimal form is most often confused with sarcoidosis or Sjogren's disease.
References:
- Weber AL, Romo LV, Sabates NR. Pseudotumor of the orbit. Clinical, pathologic, and radiologic evaluation. Radiol Clin North Am. 1999 Jan;37(1):151-68, xi. [PubMed] [MD Consult]
- Jacobs D, Galetta S. Diagnosis and management of orbital pseudotumor. Curr Opin Ophthalmol. 2002 Dec;13(6):347-51. [PubMed]
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