Mediastinal Rhabdomyoma Diagnosed by Fine Needle Aspiration Cytology

摘要

Extracardiac rhabdomyoma is a rare benign tumor of striated muscle origin which is mostly located in head and neck areas. Only four cases of adult rhabdomyomas in the mediastinum have been reported and these cases were diagnosed on surgical excision or autopsy. We report the clinical and cytological findings of a mediastinal rhabdomyoma which has been diagnosed by transesophageal endoscopic ultrasound-guided fine needle aspiration (FNA). FNA showed loose aggregates and isolated large round to polygonal tumor cells with abundant granular cytoplasm. Immunostains on the cell block showed strong positivity of tumor cells for myoglobin and desmin. This report highlights the cytologic diagnosis of this rare entity and its potential differential diagnosis. Introduction Rhabdomyoma is a rare benign tumor of striated muscle origin.1 Unlike other benign soft tissue neoplasms which are generally more prevalent than their malignant counterparts, adult rhabdomyomas are less frequent than rhabdomyosarcomas.1 Topographically, rhabdomyomas are classified into cardiac and extracardiac types based on their site of origin.2 The cardiac rhabdomyoma almost exclusively occurs in the heart of young children and is often associated with congenital abnormalities like tuberous sclerosis (50% of the cases in clinical series)4, phacomatosis or disorders of glycogen metabolism.5 Extracardiac rhabdomyomas are rare, representing only 2% of muscular tumors.3 Extracardiac rhabdomyomas are distinguished into four clinically and morphologically different types: adult (50% of extracardiac rhabdomyomas), fetal (40%), genital (10%)8, and the rare rhabdomyomatous mesenchymal hamartoma types.9 Seventy percent of extracardiac rhabdomyomas occur in the head and neck region: the most common sites are the larynx, pharynx, and the floor of the mouth.6 They may also occur in some unusual sites, such as the orbit, vagina, bladder, esophagus, trunk, and extremities.7 Although there are more than 160 cases of adult extracardiac rhabdomyomas reported in the literature9, we are aware of only four reported cases of mediastinal rhabdomyomas and these cases were diagnosed after surgical excision or at the time of autopsy.8,10,11,12 We present an incidentally identified mediastinal rhabdomyoma which was diagnosed by transesophageal endoscopic ultrasound-guided fine needle aspiration (FNA) procedure. In addition, we review the role of FNA in the diagnosis of rhabdomyomas and the main morphologic differential diagnosis in the mediastinum. Case Report The patient was 76 year old male who presented for evaluation of chronic obstructive pulmonary disease (COPD). His past medical history was significant for tobacco smoking for 25 years, hypertension, urinary tract infection, and diabetes mellitus type II. His surgical history was significant for spina bifida, hiatal hernia repair, abdominal hernia repair, and cholecystectomy. The patient denied dysphagia, dyspnea, chest pain, weight loss, or abdominal pain. On physical examination no palpable mass or lymphadenopathy was detected. A thoracic computed tomography (CT) scan was performed to evaluate his COPD and showed an incidental 5.6 x 4.2 x 2.6 cm lobulated soft tissue mass in the superior mediastinum abutting the esophagus and right thyroid lobe. The tumor did not show surrounding lymphadenopathy. An endoscopic ultrasound (EUS) was performed. Esophagoscopy was normal without evidence of an intrinsic or extrinsic mass. EUS showed a 5.0 cm x 3.2 cm hypoechoic homogenous mass extrinsic to the esophagus, without surrounding lymphadenopathy. EUS-guided fine-needle aspiration (FNA) of the mass was performed with a 22-gauge needle, totaling 6 passes. The patient has not been scheduled for surgery yet, but a followup CT scan after 12 months showed no increase in the size of this tumor. The patient has remained asymptomatic. Materials and Methods The FNA sample was evaluated at the University of California, San Diego Department of Pathology. On