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Orbital RMS is primarily a disease of young children with mean age at diagnosis of 8 years; however it can occur at any age. There is slight predilection for males with roughly a 5∶3 male to female ratio. There appears to be no racial predisposition and the tumor is invariably unilateral. Most tumors are retrobulbar resulting in proptosis but it can arise from extraconal space especially superior or superonasal area[6]. The classic alveolar RMS is composed of nets of poorly differentiated cells with central loss of cellular cohesion surrounded by a frame works of dense fibrous septa these forming irregular alveolar spaces. Alveolar tumors are more common among adolescents, often arise in the extremities and carry a worse prognosis. Embryonal RMS is by far the most common variant found in the head and neck region including the orbit. RMS are rare in patients older than 40 years, most in this age group are of the pleomorphic subtype with a reported median age range of 5056 years[7].
In 1962 Porter Field and Zimmerman refuted the prevailing assumption that embryonal RMS originate from preformed muscle. It is now widely believed and accepted that embryonal RMS arises from undifferentiated mesenchymal cells that possess the capacity to differentiate into striated muscle. The adult RMS arises from voluntary muscles and is extremely rare since fully mature muscle cells are not prone to malignant changes[8]. Patients with orbital RMS generally present with proptosis in 80%100% and globe displacement in 80%. Pain is a symptom in 10% of cases and it usually occurs in more advanced cases. Ocular motor nerve involvement result in ophthalmoplegia but recovery after initiation of chemotherapy is almost 100% due to reduction of tumor size that result in relieve compression on the nerve. In contrast to ocular motility the prognosis for visual recovery is much worse which is due to optic atrophy[9].Visual impairment is usually minimal until tumors become advanced. Concerning anatomical location RMS in the orbit produces early ocular symptoms and signs as compared to tumors in the more occult locations and this permits earlier recognition of the tumor. In addition there are few lymphatic channels in the orbital area and therefore early lymph node metastasis rarely occurs.
In adults proptosis tends to have slower course and rarely attains a large size. In regions where medical care is not readily available, RMS can attain immense proportions and destroy the eye and hence vision as in our case. CT and MRI form central part in the diagnosis of RMS and usually appear isointense or gives slightly higher signal than the extra ocular muscles and lower signal than fat on T 1weighted images, on T2 weighted images the lesion gives high signal with respect to muscle and orbital fat. Orbital RMS can invade orbital bone and extend into cranial cavity, metastasis mainly to lungs and bones; regional lymph node metastasis is rare. Distant metastasis from RMS is usually fatal in spite of intensive chemotherapy and symptomatic treatment.
In 1972 inter group RMS (IRS) study was established to increase knowledge and to improve therapeutic results for RMS from all locations. Four consecutive clinical trials had been conducted and reported. A staging classification of RMS employed by IRS, briefly group one is defined as localized disease completely resected; group two, microscopic disease remaining after biopsy, group three is gross residual disease remaining after biopsy, group four is distant metastasis present at onset. This classification can assist in selecting treatment and in predicting prognosis. This classification can also be applied to cases of orbital RMS.
Until late 1960s orbital exenteration was generally considered to be the treatment of choice for orbital RMS. However the mortality rate for patients with orbital RMS continued to be greater than 70% in early 1970s. It was gradually recognized that orbital exenteration did not provide affected patients with a better prognosis and there was a gradually trend toward treatment with limited biopsy followed by various regimens of irradiation and chemotherapy. Hence, orbital exenteration is rarely performed as primary treatment today. It may be justified for extremely advanced disease that had destroyed the eye as frequently seen in third world countries. In medically advanced countries it still employed for some aggressive tumors that have been resistant to irradiation and chemotherapy.
In late 1960s and early 1970s systemic chemotherapy was incorporated into protocols for treatment of RMS. This was usually combined with radiotherapy with continued success. The agents employed were Vincristine and Actinomycin D.In 1979 a review of orbital RMS treated with combined surgery, irradiation and chemotherapy demonstrated control of the primary tumor and salvage of the eye in over 90% of cases.
The latest management of RMS should include any combination of surgery, irradiation and chemotherapy. Surgery can be done by complete or near complete surgical removal when that can be achieved with out major damage to vital structures like the optic nerve and extra ocular muscles.
Irradiation is used as adjunct to surgery or chemotherapy for tumor recurrence after standard irradiation and chemotherapy have failed to control the tumor although external beam irradiation has been employed in such cases implant brachytherapy using a specially designed radioactive plaque has been rarely used.
Orbital RMS has very favorable outcome with Actinomycin D and Vincristine, it has been shown by latest study that addition of Ifosfomide and Etoposide can improve outcome.
Systemic chemotherapy is considered the only therapeutic option for patients presenting with widely metastatic disease or with locally advanced disease not amenable to surgery or radiotherapy[10]. For the majority of these patients cytotoxic chemotherapy should be regarded as palliative although in small subset of patients long term survival may be achieved. Combination of chemotherapy may produce higher response rate. Recent series have reported improvements in the 5year survival rate from 5% to 15% with local therapy alone to 47% to 62% with multimodal therapy.
The prognosis for orbital RMS has improved greatly in recent years. Factors that appear responsible for better prognosis for RMS in orbital region include the more favorable anatomical location, the earlier stage of the disease at the time of diagnosis, more favorable tumor morphology and perhaps patient age.
Absence of liver metastasis, young age and histopathology grade were identified as favorable factors for response to chemotherapy, while presence of bone marrow metastasis was found to be an independent cause of adverse prognostic factor.
Nodal involvement appears to be an adverse prognostic factor in both pediatric and adult RMS. A review of 1,415 patients without distant metastases in IRSI and IRSII revealed a 10% incidence of clinical nodal disease at diagnosis and a 14% incidence of pathologic lymphatic metastases at resection. Nodal involvement was particularly common in patients with genitourinary tract tumors (prevalence 24% 41%) and extremity tumors (12%), and the 3year survival rate with local regional disease was 45%, compared with 75% with localized disease.
Tumor morphology also appears to be an important prognostic indicator, with Embryonal RMS the most common type in the orbit carrying more favorable prognosis. Alveolar RMS in which translocation exist between the FKHR gene locus and either PAX3 or PAX7 thus resulting in fusion protein which is associated with better outcome.
Metastatic disease at presentation is strongly associated with poor prognosis. As in our case. Despite the recent use of multimodal therapy the prognosis in older patients appears to be worse than in children. With over all response rate was 82%.
Increase tumor size was inversely related to prognosis. The 5 year survival rates for patients with tumors less than 5 cm, 510cm, and more than 10cm were 60%, 14% and 0% respectively. The 5 year survival of those with orbital alveolar RMS was 74% and embryonal RMS was 94%[11]. The embryonal cell type constitutes 80% of orbital tumors.
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