Mediastinal fetal rhabdomyoma in nevoid basal cell carcinoma syndrome: a case report and review of the literature
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- Yang, S., Zhao, C., Zhang, Y. et al. Virchows Arch (2011) 459: 235. doi:10.1007/s00428-011-1108-8
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Fetal rhabdomyoma (FR) usually occurs in the soft tissue or mucosa in the head and neck region of young children. These tumors are divided into classic (myxoid) and intermediate (cellular, juvenile) subtypes. The intermediate subtype was first described by Di Sant'Agnese and Knowles in 1980 . This tumor is much less frequently encountered than the classic subtype and has never been reported in the mediastinum. Nevoid basal cell carcinoma syndrome (NBS) is an autosomal dominant disorder characterized by the premature appearance of basal cell carcinoma, keratocysts of the jaw, abnormalities in the skeletal, ocular, and nervous systems, and various other types of neoplasms . Here, we present the first report of a patient with intermediate FR located in the posterior mediastinum and associated NBS.
This 17-year-old male was admitted to a hospital with multiple bilateral cysts of the jaw. He also showed polydactylia of his hands. Prior to the surgical excision of these jaw cysts, a routine chest radiograph showed a mass in the left posterior–inferior mediastinum and a bifid deformity of the fourth rib. Physical examination was otherwise noncontributory, and the patient had no other past medical problems. Pathological examination showed that the cysts of the jaw were keratocysts. No other family member had keratocysts or other findings like those of this patient.
Computed tomography confirmed the presence of a 9 × 5 × 5-cm mass with a focal contrast enhancement in the lower posterior mediastinum. Upper gastroenterography showed that the lower part of the esophagus was dislocated with no sign of mucous destruction or evidence of tumor invasion.
Operative excision of the mediastinal mass was carried out 6 months after the removal of the patient's jaw cysts. The mass was located in the lower posterior mediastinum and was adherent to the lower lobe of the left lung. One side of the mass was also closely associated with the esophagus and one aspect of the tumor was peeled from the muscle layer of the esophagus, but the esophageal mucosa was not affected. The mass was completely excised.
Material and methods
The resected tumor was fixed in buffered formalin and routinely embedded for histological evaluation. Immunohistochemical stains were performed on 4-μm paraffin sections, using primary antibodies against smooth muscle actin (SMA), desmin, myoglobin, HHF35, CD117, CD34, S-100, Ki-67, and keratin (AE1/AE3). All antibodies were purchased from DakoCytomation. After incubation with primary antibody, sections were treated with polymer HRP-conjugated secondary antibodies (DakoCytomation, Inc.) and colorized with diaminobenzidene–hydrogen peroxide substrate (DakoCytomation, Inc). The nuclei were lightly counterstained with hematoxylin.
The patient was followed up with no further treatment. Over a 24-month period of follow-up to the present, he remains asymptomatic, with no evidence of recurrence or progression.
Extracardiac rhabdomyomas are uncommon benign neoplasms with striated muscle differentiation. Based on histology and location, they can be divided into three groups: fetal, adult, and genital. FR most commonly (70–90%) occurs in the head and neck region in the vicinity of the upper aerodigestive tract. A few cases have also been identified in other anatomic sites, such as the lower extremity , abdominal wall , mediastinum [5–7], retroperitoneum , and so on. Histologically, FR can be further divided into classic (myoxid) and intermediate (cellular, juvenile) subtypes. The classic FR is composed of abundant myxoid stroma, primitive “undifferentiated” mesenchymal cells, and immature striated cells, which are similar to the 6∼10-week stage of muscle development. The intermediate FR was first described in 1980  as the “cellular” type and showed a high degree of cellularity, predominance of spindle cells, and more advanced and extensive skeletal muscle maturation than fetal rhabdomyoma. This subtype was therefore also referred to as the “juvenile” type . Myxoid matrix is scare or absent in this subtype, and intermediate FR is therefore more likely to be misinterpreted as some other type of benign or malignant spindled cell tumor especially when arising in deep locations.
Based on the morphology, the case we present here is consistent with intermediate FR, but the occurrence of this tumor in the posterior mediastinum is unusual. This is the first reported case of intermediate type FR presenting in the mediastinum, although classic FRs  in the posterior mediastinum and adult rhabdomyomas in both the anterior and posterior mediastinum [6, 7] have been reported.
It is of great importance to correctly diagnose intermediate FR particularly in deep locations such as this tumor to avoid misinterpretation as a malignancy, especially rhabdomyosarcoma. The lack of nuclear dysplasia, mitoses, and necrosis and the noninfiltrative growth pattern are the key features in the diagnosis of benign rhabdomyoma. In addition, benign and malignant Triton tumors also must be excluded. Triton tumors show both neural and skeletal muscle differentiation. There was no S-100 positivity in the present tumor, excluding a diagnosis of Triton tumor.
The immunophenotypes reported for intermediate FR are not consistent in the literature. Chennagiri showed desmin+/SMA− expression in their cases . In our case, the spindle cells expressed SMA, and the cells showing features of developing skeletal muscle expressed desmin, raising the possibility that these tumor cells represent a spectrum of muscle cell differentiation.
Although there was no family history of NBS in the current case, the multiple keratocysts in the jaw, deformity of the rib, and polydactyly clearly demonstrate that this is an NBS patient. NBS showed autosomal dominant inheritance and was initially described in 1960 by Gorlin and Goltz . The classic features they described included basal cell carcinoma, odontogenic keratocysts, and bifid ribs. Since that time, various deformities and neoplasms have been recognized as associated with this syndrome. Together with the current case presented here, there have been seven reported cases of FR in NBS patients, and all have been FR of either classic or intermediate type. However, to date, no adult rhabdomyoma or rhabdomyosarcoma has been found in association with NBS [5, 9–14]. This suggests that when a tumor with definitive evidence of skeletal muscle differentiation appears in NBS, it is likely to be a benign FR. Secondly, in FRs occurring in the context of NBS, only two of the seven have been located in the head and neck region [9, 14], which is notably different from FR without NBS.
In summary, the present case underscores the importance of making the correct histological diagnosis for this rare lesion, particularly when it is found in deeper locations. Failure to recognize this tumor may lead to unnecessarily aggressive treatment. The complete removal of the mass seems to be an effective and adequate treatment for this tumor.
We gratefully acknowledge the assistance of Dr. Michael A. McNutt in editing this manuscript.
Conflict of interest
The authors declare that they have no potential conflicts of interest which would warrant disclosure.