Rhabdomyomatous mesenchymal hamartoma of oral cavity: an unusual location for such a rare lesion

Abstract

Sir, Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital lesion occurring in the skin, particularly of the face and neck [4]. The term hamartoma has been histologically proven as a lesion composed of a disordered mixture of mature adipose, skeletal muscle tissue, adnexal structures and sometimes blood vessels and nerves [4, 5]. Although RMH is usually a solitary lesion, it can be multiple and associated with uncommon congenital abnormalities [5]. The etiology of RMH is still unclear, but it is likely that an aberrant embryological development or migration of mesodermally derived tissues due to micro-environmental modifications and/or genetic factors may play a pathogenetic role. We first report two cases of RMH arising as polypoid masses of oral cavity. This is an unusual site for such a lesion, as all cases of RMH reported in the English literature (approximately 25 cases) have typically been located in the skin, with only one case occurring in the nares [2, 4]. Patient 1 is a 15-day-old female infant who presented with multiple polypoid masses of tongue, the largest one measuring 1 cm in diameter (Fig. 1A). Patient 2 is a 1-monthold male infant presenting with a single polypoid mass of the left palatine tonsil, measuring 1.5 cm in greatest dimension. In both cases, the lesions were surgically excised with free margins. After a 6-month (case 1) and 2-year (case 2) clinical follow-up, no recurrence was observed. Histological examination in both cases showed the typical features of RMH: a polypoid mass covered by squamous epithelium (case 1) or alternating squamous and respiratory type epithelium (case 2) with an underlying disordered admixture of mature skeletal muscle fibers, islands of mature adipose tissue and salivary glands (case 1) (Fig. 1B) or submucosal seromucinous glands (case 2) (Fig. 2). Characteristically, the skeletal muscle fibers haphazardly surrounded both salivary glands (case 1) or seromucinous glands (case 2). Blood vessels of venular type were found admixed among the adipose tissue. No cytological atypia, necrosis or mitosis was observed. The present case widens the anatomic location of RMH, indicating the oral cavity as a possible involved site. This is not only of academic interest, as both fetal rhabdomyoma and embryonal rhabdomyosarocma (botryoid subtype) may present as polypoid masses in the same sites [1, 3]. Unlike RMH, they lack any additional mature tissue component as integral part of the lesion. Although these tumors may contain a variable amount of differentiated skeletal muscle cells, there is a morphological spectrum of skeletal muscle differentiation, ranging from undifferentiated round to spindle-shaped to well-differentiated mature cells with cross-striations, which is not seen in RMH. G. Magro (*) Dipartimento G.F. Ingrassia, Anatomia Patologica, Universita di Catania, Catania, Italia e-mail: g.magro@unict.it Tel.: +39-95-3782024 Fax: +39-953-782023