Abstract
Rhabdomyomas are rare benign mesenchymal tumors with skeletal muscle differentiation. They are less commonly encountered than are their malignant counterparts, rhabdomyosarcomas. Rhabdomyomas fall into 2 general categories: cardiac and extracardiac types. Extracardiac rhabdomyomas are among the rarest tumors in humans and can be subclassified as fetal, juvenile, and adult types depending on the individual tumor’s degree of differentiation by light microscopy. Adult extracardiac rhabdomyoma has a strong predilection for occurrence in the head and neck, mainly in the area of larynx and pharynx. In this article, 2 cases of parapharyngeal rhabdomyoma are reported together with a review of the world literature.
1
Introduction
Rhabdomyomas are particularly rare benign tumors of soft tissue, originating from skeletal muscle cells and accounting only for 2% of skeletal muscle tumors . They are subdivided into cardiac and extracardiac types based on location . The more common cardiac rhabdomyomas are often multiple and are most often encountered in children. They are often associated with other malformations such as tuberous sclerosis (50% of the cases), phacomatosis, or disorders of glycogen metabolism. Cardiac rhabdomyomas may spontaneously regress and are believed to represent hamartomas rather than true neoplasms. The extracardiac rhabdomyomas are more rarely encountered . Extracardiac rhabdomyomas are further classified into fetal, juvenile, and adult types . The separation of these different types of rhabdomyomas is based on their histologic appearance rather than the age of the patient . In contrast to the fetal rhabdomyomas, which are generally solitary lesions, 3% to 10% of adult rhabdomyomas may be multifocal—either synchronous or asynchronous .
Adult extracardiac rhabdomyomas are rare, but morphologically characteristic, benign mesenchymal tumors with recognizable mature skeletal muscle differentiation. The adult type of rhabdomyoma occurs almost exclusively in the head and neck region (93% of all cases), particularly in the larynx and pharynx of the adult men. Adult rhabdomyomas are not known to regress spontaneously or to have an association with tuberous sclerosis .
2
Case reports
2.1
Case 1
A 71-year-old male patient was referred with dyspnea that worsened during the night and stridor. He denied other complaints, such as dysphagia or pain. Physical examination showed a soft parapharyngeal mass with some displacement of the larynx. The vocal cords moved normally. A cervical ultrasound showed a 6.6 × 4.6-cm mass on the left side at neck at level I/II.
Magnetic resonance imaging (MRI) with and without contrast medium (gadolinium-DTPA) was obtained ( Figs. 1 and 2 ). The MRI scan showed a solid, well-circumscribed tumor with a maximum diameter of 8 cm, with its epicenter inferior to the left tonsil. The tumor was semicircular and surrounded the hypopharyngeal structures on the left side of the neck, displacing the tongue base anteriorly and to the right and extending inferiorly to the level of the hyoid bone.
The patient underwent a transoral laser surgical mucous incision with subsequent biopsy of the retro- and parapharyngeal mass. Microscopically, it appeared to be a partially encapsulated mass with round and polygonal cells with predominantly peripherally placed nuclei and occasional intracellular vacuoles. There was no mitotic activity or nuclei atypia. The final histopathologic diagnosis was adult rhabdomyoma.
Definitive surgical excision of the mass via an open transcervical approach was then performed. Because the tumor mass was particularly vascular, repeated ligation with titanium clip application was necessary. The left superior thyroid cartilage cornu was also resected. The entire tumor was sent to pathology as a single specimen. Macroscopically, the mass was well defined, lobulated, and light brown, with a maximum diameter of 7.8 cm ( Fig. 3 ). Microscopically, the encapsulated tumor consisted of large polygonal cells that were demarked by a thin fibrous stroma. The surrounding host tissue consisted of normal skeletal muscle ( Fig. 4 ). The cytoplasm of many of the tumor cells contained vacuolated spaces, which represent the intracellular glycogen and which proved to be periodic acid–Schiff positive. These so-called spider cells had a condensed core of eosinophilic cytoplasm with thin strands radiating to the cell membrane ( Fig. 5 ). Cross-striations were usually present but sparse. Nuclei were round and vesicular, with one or more small nucleoli ( Fig. 6 ). There were no mitoses. The final pathologic diagnosis was adult rhabdomyoma.
Today, 1 year after treatment, the patient has no complaints; and there is no evidence of recurrent tumor.
2.2
Case 2
A 68-year-old male patient was referred with a 2-year history of a sensation of a foreign body in the throat, dysphagia, and a tendency to aspiration. He carried a previous diagnosis of oropharyngeal rhabdomyoma; and as a consequence, there was a clinical suspicion of recurrence of this previously identified tumor.
Physical examination showed a round mass in the right oropharynx that displaced the epiglottis to the left side.
Magnetic resonance imaging was carried out, both with and without contrast medium (gadolinium-DTPA). This MRI scan revealed a mass in the right oropharynx measuring 4 cm in greatest dimension, with a tumor cone expanding superiorly to the level of the tongue base on the right side, abutting the mandible ( Figs. 7 and 8 ).
Two months after this presentation, the patient underwent a transoral excision of the oropharyngeal tumor; all identifiable tumor was resected.
The tumor was sent to pathology in several individual excisional biopsy fragments that together measured 5.5 cm in greatest dimension. On cut surface, the mass was a homogeneous light brown. Microscopically, a solid tumor composed of an admixture of deeply eosinophilic polygonal cells and cells with vacuolated glycogen-rich cytoplasm was found. The cells had 1 or (rarely) 2 centrally or peripherally placed vesicular nuclei, and 1 or more prominent nucleoli. “Jackstraw” crystalline structures were also rarely observed within the cytoplasm of some of the eosinophilic polygonal cells ( Fig. 9 ). There was no mitotic activity or nuclear atypia. Cross-striations as well as intracytoplasmatic filamentary structures could be discerned.
Immunohistochemically, the cells were strongly positive with antibody to desmin ( Fig. 10 ), with a patchier pattern of positivity with antibody to muscle-specific actin (not shown). Only rare positive Ki-67 positive tumor cells were seen. The final pathologic diagnosis was oropharyngeal rhabdomyoma.
The postoperative course was uneventful, and the patient was discharged on postsurgical day 11. Today, 10 months after surgery, the patient has no complaints; and there is no evidence of recurrent tumor.
2
Case reports
2.1
Case 1
A 71-year-old male patient was referred with dyspnea that worsened during the night and stridor. He denied other complaints, such as dysphagia or pain. Physical examination showed a soft parapharyngeal mass with some displacement of the larynx. The vocal cords moved normally. A cervical ultrasound showed a 6.6 × 4.6-cm mass on the left side at neck at level I/II.
Magnetic resonance imaging (MRI) with and without contrast medium (gadolinium-DTPA) was obtained ( Figs. 1 and 2 ). The MRI scan showed a solid, well-circumscribed tumor with a maximum diameter of 8 cm, with its epicenter inferior to the left tonsil. The tumor was semicircular and surrounded the hypopharyngeal structures on the left side of the neck, displacing the tongue base anteriorly and to the right and extending inferiorly to the level of the hyoid bone.
The patient underwent a transoral laser surgical mucous incision with subsequent biopsy of the retro- and parapharyngeal mass. Microscopically, it appeared to be a partially encapsulated mass with round and polygonal cells with predominantly peripherally placed nuclei and occasional intracellular vacuoles. There was no mitotic activity or nuclei atypia. The final histopathologic diagnosis was adult rhabdomyoma.
Definitive surgical excision of the mass via an open transcervical approach was then performed. Because the tumor mass was particularly vascular, repeated ligation with titanium clip application was necessary. The left superior thyroid cartilage cornu was also resected. The entire tumor was sent to pathology as a single specimen. Macroscopically, the mass was well defined, lobulated, and light brown, with a maximum diameter of 7.8 cm ( Fig. 3 ). Microscopically, the encapsulated tumor consisted of large polygonal cells that were demarked by a thin fibrous stroma. The surrounding host tissue consisted of normal skeletal muscle ( Fig. 4 ). The cytoplasm of many of the tumor cells contained vacuolated spaces, which represent the intracellular glycogen and which proved to be periodic acid–Schiff positive. These so-called spider cells had a condensed core of eosinophilic cytoplasm with thin strands radiating to the cell membrane ( Fig. 5 ). Cross-striations were usually present but sparse. Nuclei were round and vesicular, with one or more small nucleoli ( Fig. 6 ). There were no mitoses. The final pathologic diagnosis was adult rhabdomyoma.
