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Rhabdomyosarcoma of the orbit

Dr Praveen Jha and Dr Frank Gaillard et al.

Rhabdomyosarcomas of the orbit account for approximately 10 - 20% of all rhabdomyosarcomas and are usually found in children.

Demographics and clinical presentation

As with other locations, rhabdomyosarcomas in the orbit are over represented 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.

Pathology

The vast majority of orbital rhabdomyosarcomas are of the embryonal sub type ^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.

Radiographic features

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 sub type more frequently arises in the superior orbit, whereas alveolar sub type is more common in the interior orbit ³.

CT

Rhabdomyosarcomas are typically homogeneous soft tissue masses isodense to normal muscle. The mass may extend into the eyelid or through bone into the paranasal sinuses (especially the ethmoid sinus) and superiorly into the anterior cranial fossa.

Following contrast administration, enhancement is usually present.

MRI

T1 :
- low to intermediate intensity, iso intense to adjacent muscle
- areas of haemorrhage are common in alveolar and pleomorphic sub types, but these are uncommon in the orbit ¹
T2
- usually hyper intense
C+ (GAD) : shows considerable enhancement

DSA

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.