Contrary to metastatic tumors of the omentum, primary tumors of the omentum are very rare and sporadically reported. However, a primary malignant rhabdoid tumor in the omentum is very rare. RMS rarely affects adults. AS per the Pubmed survey, only three cases have been reported yet. The rhabdoid cells show round to tear drop shape with vesicular nuclei and a single large nucleolus. There are ill-defined round to oval hyaline inclusions composed of intermediate filaments in cytoplasm [1].
Intraperitoneal RMS, and in particular with omental involvement, in any age has been rarely reported in literature [2]. In general, the symptoms of omental tumors present as abdominal discomfort (45.5 %), abdominal mass (34.9 %), and abdominal distention (15.2 %). Unfortunately, there are no specific findings differentiating the origin or nature of the mass in imaging studies due to the extent of the omentum and the adhered organs. A considerable finding is displacement of the stomach, the transverse colon, and small bowel, by an extrinsic mass [3].
The treatment of omental tumors is complete excision via omentectomy. We diagnosed the mass as a malignant rhabdoid tumor based on the typical cellular morphology and immunohistochemical stains. Immunohistochemically, the rhabdoid cells express both cytokeratin and vimentin, but not myogenic differentiation nor INI1 protein [4].
For treatment, an aggressive operation to achieve total resection is recommended because the effectiveness of chemo radiotherapy has not been proven. The classic combination of ifosfamide, carboplatinum, and etoposide is recommended, and multidrug protocols including topoisomerase I inhibitors are recommended [5].
Vincristine, actinomycin, and cyclophosphamide (VAC) compared with vincristine, Actinomycin, and Cyclophosphamide with Vincristine, topotecan, and cyclophosphamide (VAC/VTC) for intermediate rhabdomyosarcoma was done at weeks 3, 9, 21, 27, 33, 39 did not show an improvement in outcome for patients with intermediate-risk RMS. The estimated 4-year FFS rates were 73 % for VAC and 68 % for VAC/VTC, which did not differ significantly [6].
Radiotherapy plays an important role in the treatment of RMS and is a major tool in the treatment of children. A cumulative dose of between 36 and 41.4 Gy is generally sufficient to control microscopic residual disease, and doses of between 50.4 and 54 Gy are utilized to control gross residual disease. Patient is to be followed every 3 months for the 1st year, then every 6 months for the 2nd and 3rd year and then yearly after [7].