Primary Pulmonary Rhabdomyosarcoma in a Child.

A 9-year-old female presented with fever, cough, and hemoptysis for a week. The chest skiagram and contrast-enhanced computerized tomography delineated a well-defined solid lesion localized to the superior segment of the right lower lobe with features of a congenital pulmonary airway malformation. The lesion was surgically managed with a segmentectomy and histopathology confirmed a contained pulmonary rhabdomyosarcoma (RMS). No other primary site of origin was evident, and a final diagnosis of "primary" pulmonary RMS was made. She received adjuvant chemotherapy and was disease free after 6 years of surveillance. The unique clinicoradiological features of the case are discussed and the sparse literature is reviewed.

INTRODUCTION

Rhabdomyosarcoma (RMS), the most common soft-tissue malignancy in childhood, occurs as primary tumors in head and neck, genitourinary tract, and extremities. Less commonly, it occurs in sites where striated muscle is not native – lung, bile ducts, eye, peripheral nerves, and cerebellum.[1] Among pediatric intrathoracic neoplasms, primary pulmonary tumors are rare and RMS more so.[2] Across the intergroup rhabdomyosarcoma study (IRS) Group I-III reports, barely six were of primary pulmonary origin. Overall, only about twenty cases were reported till 1996 and 31 till 2010,[3] and a series of 3 has been added in 2013.[4]

CASE REPORT

A 9-year-old female presented with a week's history of fever, hemoptysis, and cough. There was no close tuberculous contact. The general examination was unremarkable. Systemic examination showed decreased air entry in the right infra-axillary area. Chest X-ray revealed a right mid zone, well-defined, homogeneous opacity. Contrast-enhanced computerized tomography (CECT) of the chest showed a 4 cm × 3 cm × 3 cm solid, noncalcified, and well-defined, iso- to hypo-dense, minimally enhancing lesion in the superior segment of the right lower lobe. An arterial feeder from the right pulmonary artery and proximity to the inferior pulmonary vein suggested a congenital pulmonary airway malformation (CPAM). The adjacent lung parenchyma was hemorrhagic; the thoracic wall and mediastinum were uninvolved [Figure 1]. Other laboratory investigations were normal. A provisional diagnosis of a congenital pulmonary mass was made. At thoracotomy, a globular, firm, hemorrhagic mass occupied the apical segment of the right lower lobe with two 1 cm lymph nodes in the main pulmonary fissure. There was no gross aberrant vasculature/hilar lymph nodal enlargement. A segmentectomy (superior segment of lower lobe) was performed with sampling of interlobar nodes. Histopathological evaluation showed a spindle cell neoplasm located centrally with surrounding normal parenchyma. The lymph nodes showed reactive changes. Immunohistochemistry was positive for actin, myosin, desmin, and MyoD. A subsequent ultrasonography (USG) of the abdomen, radioisotope bone scan, and bone marrow aspiration – biopsy were normal. A final diagnosis of a primary pulmonary RMS (IRS-Group 1) was made. She received the standard scheduled chemoradiotherapy with vincristine, adriamycin, cyclophosphamide (ten cycles, at 3 weekly intervals) at the regional referral oncology center and periodic clinicoradiological surveillance (biannual) thereafter. At 6-year follow-up, she was asymptomatic and disease-free [Figure 2].

Figure 1

Contrast-enhanced computerized tomography of the thorax (axial, a -mediastinal window, b -pulmonary window, and c-coronal sections) delineating a well-defined pulmonary mass in the superior segment of right lower lobe

Figure 2

Contrast-enhanced computerized tomography of the thorax (axial sections: a – mediastinal window, b – pulmonary window) at 6-year follow-up

DISCUSSION

RMS originates from pluripotent primitive mesenchyme with capacity for differentiation into neurogenic and myogenic elements. Two theories explain the histogenesis of primary pulmonary RMS. The first proposes an origin from heterotopic islets of striated muscle, hence, the association with CPAM (bronchogenic cysts, cystic adenomatoid malformations, and extralobar sequestration) where abnormal lung tissue harbors such islets.[5] It is held that pleuropulmonary blastomas in such cystic lesions have the potential to evolve into high-grade primitive sarcomas.[6] Indeed, pulmonary sarcoma is more common than carcinoma in CPAM. Myxosarcoma, reticulosarcoma, and hemangiopericytoma have all been described within cystic lesions of the lung in children.[3] Although the CECT suggested a CPAM and the lesion was segmental, operative findings and histological features were otherwise. It is conjectural whether a preexisting malformation was lost in the neoplastic growth. The second theory suggests a metaplasia of uncommitted mesenchymal cells in a normal lung like in other organs lacking intrinsic skeletal muscles, e.g., bile ducts, eye, peripheral nerves, and cerebellum.[1] Probably, this theory explains the described case.

The common symptoms at the onset are nonproductive cough, low-grade fever, and dyspnea; tumors abutting on the airway produce obstructive symptoms. Acute respiratory distress with spontaneous pneumothorax is characteristic of neoplasms within a congenital lung cyst.[7] Metastases present variably depending on the location. Productive cough and hemoptysis were unusual features here. Some are incidental discoveries as localized opacities on chest skiagrams. Common radiological features include lobar/segmental atelectasis and pleural effusion. An ipsilateral reactive/malignant pleural effusion may opacify the hemithorax and obscure a mass.[3] Although USG is suggestive, CECT/magnetic resonance imaging provides accurate details. The primary lesion may be poorly/well-defined and solid/mixed/cystic. Involvement and infiltration of the chest wall, mediastinum, and diaphragm are evaluated.[8] Nodules protruding along the periphery of a cystic mass suggest a neoplasia. The well-circumscribed segmental appearance with a suspicious pulmonary vascular supply on CECT mimicked a CPAM.

The two major histological subtypes of RMS, embryonal and alveolar, have unique histological appearances and distinctive molecular genetic abnormalities. Embryonal tumors comprise two-thirds of all RMS and are have stroma-rich spindle cell histology. The expression of muscle-specific proteins confirms the diagnosis in unusual locations like ours. The tumor was well contained and the nodes showed reactive changes; hence, we have elected not to intervene surgically again. Similarly, in keeping with IRS 1–3 experience, no radiotherapy was used.[9]

A variety of factors influence the overall prognosis and survival in primary pediatric pulmonary RMS. Schiavetti et al.[7] and others[1] opine that the presence of simultaneous cystic lesion is a linked to early detection, complete surgical removal, and an overall favorable prognosis. Site-wise, thoracic RMS usually presents late with a large tumor burden. Larger tumors (>5 cm) and metastatic disease (regional/systemic) at diagnosis and residual disease following the primary surgery have a poorer prognosis.[710] The described case had several favorable prognostic factors – size <5 cm, histological clear margins, tumor-free regional lymph nodes, and localized. Although she has been well for 6 years, a small but appreciable incidence of the second malignant neoplasms arising in children who have survived RMS mandates a close follow-up and surveillance for many years.[11]

CONCLUSION

Primary pulmonary RMS, though anecdotal in children, should be considered in young patients with a solitary pulmonary mass. Although the noncystic form of the neoplasia is conventionally associated with a late presentation and poor prognosis, this case illustrates a favorable presentation. A clear protocol of management is slowly emerging with cumulative experience, and early diagnosis affords an opportunity for effective multimodality management and favorable survival.

FINANCIAL SUPPORT AND SPONSORSHIP

Nil.

CONFLICTS OF INTEREST

There are no conflicts of interest