Soft tissue sarcomas(STS) are an unusual finding mainly affecting the pediatrics population. Rhabdomyosarcomas account for more than half of them. This percentage drops significantly in adults where it doesn't exceed 2–5%.
Rhabdomyosarcoma seems to originate from any immature mesenchymal cells regardless of what it was dedicated for.
Its pathogenesis is still poorly understood. Mutations in macrophage inhibitory factor (MIF) and p53 are responsible for tumor progression.Compared to pediatric RMS which has clear risk factors such as prenatal drug exposure and X ray, there are no studies published regarding the etiology of RMS in adults.
Stout et al in 1946 was the first to classify Rhabdomyosarcoma tumors. However, in 1956 Horn et al proposed the widely-used classification which comprises the embryonal, botryoid (a subtype of embryonal), alveolar (20% of cases and has the worst prognosis) and pleomorphic types. Whereas WHO classifies this tumor into Embryonal, alveolar,pleomorphic, and spindle cell/sclerosing RMS. The first well described Alveolar Rhabdomyosarcoma case was done by Riopelle et all in 1956.
Alveolar RMS, consists 20–30% of RMS in patients whose ages are 15 to 20 years old. It arises mostly from the deep soft tissue of the extremities, paraspinal, perineal regions and the paranasal sinuses.
Omental rhabdomyosarcoma in adults is uncommon and very rare as a primary site. All previous cases were alveolar. Here we perform a literature review of alveolar rhabdomyosarcoma of omentum. We have excluded two cases because they were not in english.
Consequently, six cases were studied with our case being the seventh one. Five of the seven cases were men. Ages ranged between 21 and 85 years old [Table 1].
Symptoms of omental tumors including ARMS are nonspecific and mass related, most commonly: abdominal discomfort (45.5%), abdominal mass (34.9%), and abdominal distention (15.2%). Other symptoms depending on our review were constipation(42.8%) followed by nausea and vomiting (28.5%), weight loss (28.5%) and pyrexia was an odd complaint in one case.
Ultrasonography (US) is usually the first performed investigation for abdominal complaints. The tumor is reported as a well defined mass with mixed echogenicity in most of the studies reviewed. MRI is the gold standard for RMS in the abdominal region. The mass appears hyperintense on T2, hypointense on T1 with heterogeneous enhancement.
Computed Tomography (CT) was widely used in most reviewed cases. RMS was described as a large, well defined and solid mass. Although no clear pattern of enhancement was found in the literature, one case mentioned mild enhancement.
PET scan defines the successfulness of treatment by detecting residual tumor, local recurrence and metastatic spread.
Metastatic cells most commonly affect lungs. But they also spread to bone, subcutaneous tissues, lymph nodes, liver, myocardium, kidney, adrenal glands, and the brain.
Definitive diagnosis can not be made on the basis of imaging studies as it has no pathognomonic sign and the diagnosis is made on the light of microscopy and immunostaining. The differential diagnosis encompass blue small round cell tumors: Ewing Sarcoma or primitive neuroectodermal tumor, Non-Hodgkin lymphoma (particularly B-cell lymphomas), Neuroblastoma, Desmoplastic small round cell tumor, Epithelioid sarcoma, poorly differentiated monophasic synovial sarcoma, clear cell sarcoma (previously known as malignant melanoma).
The gross appearance of ARMS is similar to all rhabdomyosarcomas. It appears as well-circumscribed nodular firm masses ranging in consistency and size. Cystic degeneration and areas of necrosis were mentioned in many studies.V Sennu et al reported increased vascularity within the tumor. Histologically, the tumor appears as irregular alveolar space made of sheets of predominantly small and round cells with abundant eosinophilic cytoplasm, small oval nuclei and prominent nucleoli separated by a fibrous septa. Mitotic figures and spindle cell myoblasts can also be seen.
Cross-striations which are the standard for RMS diagnosis can only be seen in 50–60% of cases, but among the 6 cases in the literature regarding the alveolar type only Sanjay Kumar Yadav et al mentioned it. On electron microscopy Z-bands can be identified. Immunohistochemistry reveals positivity for Desmin, Myogenin, MYOD-1, and Vimentin. Monoclonal antibodies against desmin, muscle specific actin, sarcomeric actin and myoglobin have a high specificity and sensitivity for diagnosing the myogenic nature of the tumor.
Treatment of RMS should be multidisciplinary according to the Intergroup Rhabdomyosarcoma Study (IRSG). Complete resection is essential and further excision is indicated if microscopic extensions were found. Concerning chemotherapy, all patients must receive a combination therapy of Vincristine, Actinomycin-d, Cyclophosphamide, Etoposide or Ifosfamide and Irinotecan to attain long term control of the tumor. Chemotherapy also improves survival and should be admitted shortly after diagnosis or after resection to encounter any metastasis. Nonetheless, Hawkins et al recommended against this as they have not seen any increase in survival rate in the adult population. Lastly, radiotherapy which has been used widely for the treatment of RMSs in infants has a significant role in reining residual disease. Doses between (36 and 54) Gy are usually utilized.
A follow up should be scheduled every 3 months in the first year, then every 6 months for the next two years and then once every year.
Prognostic factors for adult RMS (regardless of subtypes as they were insignificant prognostically) include: age, tumor size, extent of disease, and margin status. On the other hand Nestor F. Esnaola et al in their study which was published in the same year indicated the absence of association between these factors and survival rate in patients who underwent multimodellary treatment. Mostly, adults had significantly worse outcomes than children (5-year overall survival rates, 27%±1.4% and 61%±1.4%, respectively; P < .0001). In our review, 3 patients out of 7 died shortly after presentation including our case. Bad response to chemotherapy is a predictor of unfavorable outcomes.
We couldn't perform MRI or full body CT because the patient died before his scheduled date.
We couldn't get any image from the laproscopy nor the previous endoscopy.
We couldn't conduct more immunostaining examinations due to the shortage of these materials.
In our review we excluded two cases: "Alveolar rhabdomyosarcoma originating from the greater omentum" by H Svanholm as it was not in english and we couldn't reach a scanner version and "Alveolar Rhabdomyosarcoma: apropos of a rare location” by Petit ML et al as the tumor arises from mesentery and it was in french.