Head & neck imaging
Case TypeClinical Cases
AuthorsG. Ege, H. Akman, H. Ege*
Patient56 years, male
The patient was screened with ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI). An enlarged superior rectus muscle was seen on US (Siemens Elegra, Erlangen, Germany, 7.5MHz linear transducer) and increased vascularity was noted with power Doppler (Figure 1). On orbital CT (Siemens Somatom Plus 4, Erlangen, Germany), isolated involvement of the right superior rectus muscle was detected (Figure 2). Optic nerves and periorbital fatty tissues were normal. Post-contrast scans showed enhancement. On MR imaging (Siemens Magnetom Open, Erlangen, Germany), the enlarged superior rectus muscle was isointense to other muscles on T1-weighted images and slightly hyperintense to periorbital fat on T2-weighted images (Figure 3). After contrast injection, markedly enhancement was seen. Following steroid therapy, symptoms resolved quickly so that the final diagnosis of orbital myositis was based on the response to steroids.
Although the disease is very seldom seen in children, a case with bilateral proptosis has been reported (3).
The inflammatory infiltrate, which is composed of polymorphic leukocytes, lymphocytes, and plasma cells, interspersed with a variable amount of fibrovascular tissue, may be diffuse or localised (4). In the very early stages of the disease, oedema and inflammatory infiltrate are evident; as the disease evolves, fibrosis and collagen fibrils are laid down. Typically, this process responds dramatically to treatment with corticostreoids.
The affected muscle shows irregular enlargement with extension into its tendinous insertions. The most commonly affected extraocular muscle is the medial rectus. Lateral rectus muscle enlargement with extension into an enlarged lachrymal gland is a relatively common manifestation of this disease (2). Also, isolated inflammation of the superior oblique muscle has been rarely reported in the literature (5).
Pseudotumour, Graves' disease and lymphoproliferative disease are the most common ophthalmological disease entities requiring evaluation by CT and MRI (4). On CT, orbital myositis shows enlargement of one or more of the extraocular muscles that extends anteriorly to involve the insertion of the muscle tendon (1). Involved muscle is usually isodense to slightly hyperdense compared with other muscles before the injection of contrast (2). Classically, the enlarged muscle has rugged, fluffy borders caused by infiltration of the surrounding fat by the inflammatory process.
Characteristic MR findings include extraocular muscle enlargement without dramatic changes in signal intensity (usually isointense to normal muscle) on T1-weighted images. On T2-weighted images, the involved muscle is isointense to minimally hyperintense compared with unaffected extraocular muscle tissue (1,2). In exceptional cases, the muscle can become markedly hyperintense. Homogeneous enhancement is usually seen within the involved muscle on CT or MR scans after intravenous contrast administration.
In differential diagnosis, various pathologies such as neoplastic (lymphoma, rhabdomyosarcoma, myeloma, neuroblastoma, leukaemic extraocular muscle infiltration, metastases), thyroid orbitopathy (Graves' disease), amyloidosis, granulomatous inflammation (e.g., fungal infection, tuberculosis, sarcoidosis), Wegener's granulomatosis, Tolosa-Hunt syndrome (with orbital involvement), traumatic (haematoma, orbital blow-out fracture with extraocular muscle herniation), and vascular (arteriovenous malformation, haemangioma, lymphangioma) should be considered (1,2).
Early recognition of orbital myositis may improve the change of a successful clinical outcome. In fact, the final diagnosis is often based on response to steroids. Biopsy is rarely indicated; it is reserved for the infrequent lesions that are steroid unresponsive.
[1] 1. Atlas SW, Galetta SL. The orbit and visual system. In Atlas SW (ed) MRI of the brain and spine. 2nd ed. Lippincott-Raven, Philadelphia, pp1030-4 (1996).
[2] 2. Bilaniuk LT, Atlas SW, Zimmerman RA. The orbit. In Lee SH, Rao KCVG, Zimmerman RA (eds) Cranial MRI and CT. 3rd ed. McGraw-Hill, New York, pp131-4 (1992).
[3] 3. Aydin K, Narin N, Erkilic K, Kurtoglu S, Hallac IK, Poyrazoglu MH. Bilateral proptosis caused by orbital myositis. A case report. Turk J Pediatr 1998; 40:135-8. (PMID: 9673541)
[4] 4. Weber AL, Romo LV, Sabates NR. Pseudotumor of the orbit. Clinical, pathologic, and radiologic evaluation. Radiol Clin North Am 1999;37:151-68. (PMID: 10026735)
[5] 5. Stidham DB, Sondhi N, Plager D, Helveston E. Presumed isolated inflammation of the superior oblique muscle in idiopathic orbital myositis. Ophtalmology 1998;105:2216-19. (PMID: 9855149)
URL: | https://www.eurorad.org/case/1251 |
DOI: | 10.1594/EURORAD/CASE.1251 |
ISSN: | 1563-4086 |