Rhabdomyosarcomas of the orbit account for approximately 10-20% of all rhabdomyosarcomas and are usually found in children.
As with other locations, rhabdomyosarcomas in the orbit are overrepresented in males, and in Caucasians. They typically occur in children below the age of 15 years.
Clinical presentation is typically with a rapidly enlarging mass, often in the upper inner quadrant 1. It is usually painless but causes proptosis and diplopia. Often the mass invades the eyelid causing marked oedema 1.
The vast majority of orbital rhabdomyosarcomas are of the embryonal subtype 1,3. Contrary to early belief, these tumours do not arise from the extraocular muscles, but rather develop from primitive mesenchymal cells that go on to differentiate into striated muscle cells 3.
CT and MRI are the modalities of choice for assessment of these masses, and to delineate adjacent structures.
It is important to report the location of the tumour epicenter as there is a correlation between location and histology: embryonal subtype more frequently arises in the superior orbit, whereas alveolar subtype is more common in the interior orbit 3.
Rhabdomyosarcomas are typically homogeneous soft tissue masses isodense to normal muscle. The mass may extend into the eyelid or through the bone into the paranasal sinuses (especially the ethmoid sinus) and superiorly into the anterior cranial fossa.
Following contrast administration, enhancement is usually present.
- low to intermediate intensity, isointense to adjacent muscle
- areas of haemorrhage are common in alveolar and pleomorphic subtypes, but these are uncommon in the orbit 1
- usually hyperintense
- T1 C+ (Gd): shows considerable enhancement
Treatment and prognosis
The mainstay of treatment is now a combination of radiotherapy and chemotherapy, which has achieved 5-year survival of over 90% for patients with embryonal rhabdomyosarcomas 2-3. In the small group of patients with alveolar rhabdomyosarcoma of the orbit, survival is lower but still good (75%) 3.
Radical surgery is no longer performed, with only a biopsy performed in many instances to confirm the diagnosis. (thus most tumours are Stage 1, Group III) 3. In some centres, extensive surgery is still performed to debulk the tumour 3.
The differential is essentially that of an orbital mass, and includes 4-5:
- 1. Weiss SW, Goldblum JR, Enzinger FM. Enzinger and Weiss's soft tissue tumors. Mosby Inc. (2001) ISBN:0323012000. Read it at Google Books - Find it at Amazon
- 2. Mccarville MB, Spunt SL, Pappo AS. Rhabdomyosarcoma in pediatric patients: the good, the bad, and the unusual. AJR Am J Roentgenol. 2001;176 (6): 1563-9. AJR Am J Roentgenol (full text) - Pubmed citation
- 3. Karcioglu ZA, Hadjistilianou D, Rozans M et-al. Orbital rhabdomyosarcoma. Cancer Control. 11 (5): 328-33. Cancer Control (link) - Pubmed citation
- 4. Burgener FA. Differential diagnosis in magnetic resonance imaging. Thieme Publishing Group. (2002) ISBN:313108121X. Read it at Google Books - Find it at Amazon
- 5. Weir J, Murray AD. Mosby's atlas and text of clinical imaging. Mosby Inc. (1998) ISBN:0723425558. Read it at Google Books - Find it at Amazon