Background
Rhabdomyoma is a lesion of striated muscle. The 2 types of rhabdomyoma are neoplastic and hamartoma. The neoplastic variety is subclassified into adult, fetal, and genital types. Hamartomas are divided into cardiac rhabdomyoma and rhabdomyomatous mesenchymal hamartomas of the skin.
Rhabdomyoma is an exceedingly rare tumor. Some investigators believe that mature striated muscle is unlikely to develop tumorous tissue. Therefore, they believe that rhabdomyoma may arise from fetal rests.
Rhabdomyoma is diagnosed most often in men aged 25-40 years. However, the so-called fetal rhabdomyoma chiefly affects boys between birth and age 3 years.
Most rhabdomyomas involve the head and neck regions.[1] The cardiac rhabdomyoma, which is believed to be a hamartoma, usually is diagnosed in the pediatric age group. However, hamartomas are benign tumorlike growth made up of normal mature cells in abnormal number or distribution. While malignant tumors contain poorly differentiated cells, hamartomas consist of distinct cell types retaining normal functions. Because their growth is limited, hamartomas are not true tumors.
Pathophysiology
The adult rhabdomyoma is a rare tumor. Very few cases have been reported in the literature. This tumor usually presents as a round or polypoid mass in the region of the neck. The head and neck area harbors 90% of adult rhabdomyomas and should be considered in a differential diagnosis in this region.[2] Studies in immunohistochemistry confirm that the tumors are almost totally matured neoplasms of clonal origin. The mass is usually asymptomatic. However, the mass may compress or displace the tongue, or it may cause partial obstruction of the pharynx. Consequently, the patient may experience some hoarseness, difficulty breathing, and difficulty swallowing.
The histopathology of adult rhabdomyoma is characterized by the presence of well-differentiated large cells that resemble striated muscle cells. Cross-striation has been demonstrated by phosphotungstic acid hematoxylin (PTAH), muscle specific actin, desmin, and myoglobin while dystrophin is shown to be expressed in the cell membranes. The cells are deeply eosinophilic polygonal cells with small peripherally placed nuclei and occasional intracellular vacuoles. Adult rhabdomyoma usually is localized to the oropharynx, the larynx, and the muscles of the neck.
Fetal rhabdomyoma occurs most often in the subcutaneous tissues of the head and neck in children between birth and age 3 years. The histopathology of fetal rhabdomyoma reveals the presence of a mixture of spindle-shaped cells with indistinct cytoplasm and muscle fibers, which resemble striated muscle tissue observed in intrauterine development at 7-12 weeks. The fetal rhabdomyoma is usually found in the subcutaneous tissues of the head and neck.
Genital rhabdomyoma most often involves the vagina or vulva of young or middle-aged women.[3] Most patients are asymptomatic. However, some patients have dyspareunia. The histopathology of genital rhabdomyoma reveals a mixture of fibroblastlike cells with clusters of mature cells containing distinct cross-striations and a matrix containing varying amounts of collagen and mucoid material. The genital rhabdomyoma usually presents as a polypoid or cystlike mass involving the vulva or vagina.
Cardiac rhabdomyoma is a hamartomatous lesion that occurs most often in the pediatric age group.[4] Cardiac rhabdomyomas typically develop in utero and are often detected on prenatal ultrasound. It usually involves the myocardium of both ventricles and the interventricular septum. Cardiac rhabdomyoma is considered a hamartomatous proliferation frequently associated with tuberous sclerosis of the brain, sebaceous adenomas, and various hamartomatous lesions of the kidney and other organs. The association of tuberous sclerosis and cardiac rhabdomyoma is important and has usually been explained by strong clinical association. Molecular evidence of this association have now been identified as the TSC2 gene missense mutation (E36; 4672 G>A, 1558 E>K TSC2).[5]
Rhabdomyomatous mesenchymal hamartoma is usually diagnosed in male and female newborns and infants. The histopathology of rhabdomyomatous mesenchymal hamartoma of the skin reveals that the lesions are located in the subcutis and contain poorly oriented or perpendicular bundles of well-differentiated skeletal muscle with islands of fat, fibrous tissue, and occasionally proliferating nerves.[6]
Malignant transformation of rhabdomyomas are very rare though there are few case report in literature.
Epidemiology
Frequency
United States
Rhabdomyoma is an extremely rare tumor compared to other soft tissue tumors. Specifically, in the category of benign primary tumors of the heart, rhabdomyoma has a relative incidence of 5.8%.
International
Rhabdomyoma is rare. Exact data regarding its incidence within populations have not been cited. In the world literature, 14 cases of multifocal adult head and neck rhabdomyoma are reported.[7]
Mortality/Morbidity
- The morbidity of rhabdomyoma depends on the type of lesion and its location. This is a benign tumor of striated muscle. Metastases have not been associated with this tumor.
- Cardiac rhabdomyomas are associated with the potential for flow abnormalities if they grow to sufficient size to restrict the left ventricular outflow tract. Although many are asymptomatic, some affected patients become symptomatic in the perinatal period. The types of clinical manifestations were illustrated in a report that included 15 children with cardiac rhabdomyoma (12 with tuberous sclerosis): the clinical presentation was heart failure or a cardiac murmur in 6 patients each, and arrhythmia in 3.[8] Based on clinical and molecular evidence, the diagnosis of fetal cardiac rhabdomyoma should lead to the careful evaluation of other fetal structures, including brain and renal parenchyma, to search for signs of tuberous sclerosis.
Race
Rhabdomyoma has been identified in all racial groups. No predilection for any particular racial group exists.
Sex
Adult rhabdomyoma has been diagnosed mostly in men. Some reports exist of cases in women. Fetal rhabdomyoma affects boys. Genital rhabdomyoma affects young and middle-aged women. Cardiac rhabdomyoma is observed in men and women. Rhabdomyomatous mesenchymal hamartoma of skin is observed in male and female newborns and infants.
Age
Adult rhabdomyoma occurs in older adults. These patients are usually older than 40 years. Fetal rhabdomyoma occurs between birth and age 3 years. Genital rhabdomyoma is observed in young and middle-aged women. Cardiac rhabdomyomas occur chiefly, but not exclusively, in the pediatric age group. Rhabdomyomatous mesenchymal hamartoma of the skin is observed in newborns and infants.
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