Primary intrathoracic tumors arising from the lung in the pediatric age group are extremely rare and represent a wide spectrum of pathological conditions (pneumoblastoma, RMS, fibrosarcoma, mucoepidermoid carcinoma, pulmonary endodermal tumour and benign tumours)5,7
. RMS, one of these rare pathological conditions, originates from primitive mesenchyme that has retained the capacity for striated skeletal muscle differentiation. RMS can arise at any site, even where striated muscle is not normally present, presumably from pluripotent cells that are capable of differentiating into neurogenic and myogenic elements. The head and neck are the most frequent sites of origin for RMS1,2
. RMS occasionally arises in the trunk, chest wall, abdomen (including the retroperitoneum and biliary tract), and the perineal/anal region8,9
. Intrathoracic region is a less common localization for RMS10-14
. Primary pulmonary rhabdomyosarcomas are extremely rare and occur in a minority of patients with thoracic rhabdomyosarcomas. Prior to this case, a literature rewiev disclosed only thirty reported cases of primary pulmonary rhabdomyosarcomas3,4
. Primary pulmonary RMS can be divided into two groups: tumors in the normal lung, and tumors in congenital cystic malformation of the lung4,6,10
. Tumor behavior is different in each group. Some investigators have reported that the presence of cystic malformations can be considered as a favorable prognostic feature in pediatric patients with pulmonary RMS4
. This seems to be due to early detection and complete surgical removal of the tumor associated with cystic lesions. In our case there was no pre-existing lung malformation. According to the data of the 31 reported cases with follow-up (3 months to 12 years), there were 16 patients who had associated cystic lesions. The number of disease free patients were 11/16 (68%) with associated cystic lesions and 7/15 (46%) in the group without any detectable lung cysts4-6
. The site of the primary tumor is an important determinant of the prognosis. Thoracic RMS usually presents late and has become quite large by the time of diagnosis. The tumor burden at diagnosis is also a statistically significant prognostic factor. Patients with smaller tumors (<5 cm) have improved survival compared with children with larger tumors, whereas children with metastatic disease at diagnosis have the poorest prognosis3,15,16
. In addition, patients with otherwise localized disease but with proven regional lymph node involvement have a poorer prognosis than patients without regional nodal involvement17,18
. In our case, the big tumor burden was the leading cause of the short survival. The extent of disease following the primary surgical procedure (i.e., the clinical group) is another determinant of outcome1
. In the IRS III, patients with gross residual disease after initial surgery (Clinical Group III) had a 5-year survival rate of approximately 70% compared with a greater than 90% 5-year survival rate for patients with no residual tumor after surgery (Clinical Group I)1,19
. In our case, gross total or incomplete resection of the tumor was not feasible. The eventual poor prognosis was inferred by the big tumor burden, unresectability of the tumor mass and the probable absence of a preexisting pulmonary cystic malformation.
Primary pulmonary RMS, although very rare in the pediatric age group, should be considered in young patients with a pulmonary mass. Since it usually presents as a large mass at the time of diagnosis that is adherent to adjacent vital structures, wide and complete resection of the primary tumor is less applicable. For this reason, we recommend that RMS should be considered in the differential diagnosis of children with persistent pulmonary symptoms or abnormalities on chest X-ray.