A 33-year-old woman with no known medical history presented with keratoconjunctivitis. Her primary care provider ordered an MRI examination of the orbits (Figure 1).
Infiltrative orbital mass
The differential diagnosis for an infiltrative orbital mass depends in large part on patient age, presence or absence of pain, history of systemic disease, known underlying primary neoplasm, and involved orbital structures. The primary diagnostic considerations for an infiltrative orbital mass in an adult woman include orbital pseudotumor, lymphoma, sarcoidosis, and metastatic disease. As these processes may have overlapping imaging appearances, clinical history is of utmost importance in rendering an appropriate list of differential diagnoses.
Orbital pseudotumor is an idiopathic orbital inflammatory process that typically presents clinically with an acute onset of pain, swelling, ophthalmoplegia, diplopia and proptosis.1,2 Clinical and imaging findings are unilateral in approximately 75% of cases. Although patients of all ages may be affected, the mean onset of clinical presentation is 50 years of age. Orbital pseudotumor has a variety of presentations, including localized or diffuse forms that may involve any orbital structure. On MRI, orbital pseudotumor is typically iso- to hypointense relative to muscle on T1 sequences, relatively hypointense on T2 sequences, and demonstrates diffuse enhancement.2 It may be classified according to the orbital structures involved, to include myositic, lacrimal, anterior, diffuse and apical subtypes. Of note, the myositic subtype affects both the extraocular muscle belly as well as its myotendinous junction, which helps distinguish orbital pseudotumor from thyroid ophthalmopathy, which typically spares the myotendinous junctions. Patients often respond well to steroid therapy.
Orbital lymphoma is the most prevalent orbital neoplasm in patients over age 60, commonly presenting with a palpable mass, proptosis and mildly restricted ocular motility. Clinical and imaging manifestations may be unilateral or bilateral. The presence of pain is fairly uncommon. While the tumor can vary in appearance from ill-defined and diffuse to a well-circumscribed mass, a helpful distinguishing feature is its ability to mold to orbital structures.3 On MRI, orbital lymphoma has variable signal characteristics but typically appears isointense on T1, and iso- to hyperintense on T2 sequences with fairly uniform contrast enhancement.3,4 Histologically, these tumors occur along a spectrum from benign lymphoid hyperplasia to lymphoma, with non-Hodgkin Mucosa-Associated Lymphoid Tissue (MALT) lymphoma being the most common.3,4
Sarcoidosis is a systemic granulomatous disease with numerous manifestations throughout the body, including the pulmonary, gastrointestinal, musculoskeletal, and central nervous systems. It most commonly occurs in the second to fourth decade of life. Noncaseating granulomas are a hallmark of the disease. Ophthalmic lesions develop in approximately 25% of patients with sarcoidosis, and visual abnormalities represent the most common extra-thoracic manifestation.5 Imaging characteristics are similar to and have significant overlap with orbital pseudotumor; virtually any orbital structure may be involved, including the globe, conjunctiva, extraocular muscles, retrobulbar space, lacrimal gland, and optic nerve.5
A number of malignancies are known to metastasize to the orbit, including breast, bronchogenic carcinoma, prostate and melanoma.3 The location within the orbit may be a clue to the primary malignancy. Breast cancer tends to metastasize to fat and muscle, melanoma to muscle, and prostate to bone. Scirrhous breast cancer will cause enophthalmos due to desmoplastic fibrosis.3 A known primary malignancy and other sites of metastatic disease should raise suspicion for metastases to the orbit in the setting of an orbital mass.
This case demonstrates the importance of differential diagnosis in the setting of an infiltrating orbital mass. In a young patient without a known history of sarcoidosis or primary malignancy, orbital pseudotumor and lymphoma become primary differential considerations. Both entities have protean manifestations and may involve any orbital structure. A useful differentiating feature is the presence of pain: Orbital pseudotumor is typically painful, while lymphoma is typically painless. Given the history of keratoconjuctivitis and rapid response to steroid therapy, the diagnosis of diffuse orbital pseudotumor was established. Otherwise, a tissue biopsy would have been required.
Infiltrative Orbital Mass. J Am Osteopath Coll Radiol.