Classical angiomyolipomas are benign tumors composed of various tissues, including fat, abnormal blood vessels and smooth muscle cells. The present study reports a male patient affected by mediastinal angiomyolipomas with massive chylous pleural effusion. The tumors were characterized with histological and immunohistochemical methods.

 2012;125(5):945-946

Classical angiomyolipomas are benign tumors composed of various tissues, including fat, abnormal blood vessels and smooth muscle cells. The present study reports a male patient affected by mediastinal angiomyolipomas with massive chylous pleural effusion. The tumors were characterized with histological and immunohistochemical methods. Although angiomyolipomas frequently occur in the kidneys of patients with tuberous sclerosis complex, it is rare that chylous pleural effusion caused by mediastinal angiomyolipomas located in the anterior, central, and posterior mediastinum.

 

 

A 50-year-old man presented with an approximately 10-day history of dyspnea and dry cough. The patient's medical history included retroperitoneal tumor resection and right nephrectomy 12 years previously. Abdominal computed tomography showed a large (15.0 cm×10.6 cm×8.7 cm), smoothly marginated retroperitoneal mass that was adhered to the right kidney (Figure 1). Histopathological evaluation revealed that the mass was an angiomyolipoma. The previous year, the patient was admitted to the hospital with symptoms of dyspnea and dry cough. Radiological and interventional diagnostics revealed massive chylous pleural effusion. An X-ray showed a mediastinal mass and massive hydrothorax. Computed tomography revealed a large (23.0 cm×10.8 cm×5.3 cm) posterior mediastinal mass (Figure 2). Magnetic resonance imaging showed an irregular right posterior mediastinal mass of predominantly fat signal intensity with internal septations (Figure 2). Because the lesions were typically well circumscribed and benign in the present patient, we first attempted resection through video-assisted thoracic surgery. A large amount of chylous liquid in the right hemithorax and compact adhesion were detected, and the procedure was then converted to open thoracotomy. The masses were appreciated within the right side of the mediastinum, and the sizes of the tumors were 5.8 cm´4.5 cm, 18.0 cm´2.5 cm, and 15.0 cm´12.0 cm in the anterior, middle, and posterior mediastinum, respectively. The tumors were easily dissected free from the surrounding structures (posterior mediastinum, esophagus and pericardium) and subsequently resected. On pathologic examination, the gross specimens had an appearance consistent with adipose tissue hyperplasia. Histological examination showed a predominance of mature adipocytes with some spindle cells and vessels, all of which exhibited minimal pleomorphism. Immunohistochemical staining demonstrated the classical composition of angiomyolipomas with positivity of melanoma tumor cells (HMB45) (Figure 3).

 

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Figure 1. Computed tomographic scan of the abdomen showed a large circumscribed tumor with a few strips of slight enhancement in the retroperitoneum. The tumor clung to the right kidney. Figure 2. Radiological and surgical findings of mediastinal angiomyolipomas. Magnetic resonance imaging showed an irregular mass located in the right posterior mediastinum in front of the spine (2A and 2B). Computed tomography showed a large circumscribed tumor with a few strips of slight enhancement in the posterior mediastinum beside the spine and an extensive water-equivalent mass in the right thorax cavity (2C). Intraoperatively, there was approximately 1000 ml of chyliform fluid in the right pectoral cavity, and a mass was appreciated within the right side of the posterior mediastinum (2D).

 

 

Angiomyolipomas are choristomas consisting of blood vessels, smooth muscle and fat. These noninvasive lesions characteristically manifest in renal tissue and have a strong association with tuberous sclerosis and lymphangioleiomyomatosis. Renal angiomyolipomas are involved in approximately 8% of patients with tuberous sclerosis and nearly 50% of patients with lymphangioleiomyomatosis.^1,2

 

Angiomyolipomas are rare; benign mesenchymal tumors are usually found in the kidney. Extrarenal manifestation of angiomyolipomas is uncommon. The most frequently reported extrarenal location is the liver. To our knowledge, only 11 cases of mediastinal angiomyolipomas have been reported in the literature (Table 1). The present case is the first description of mediastinal angiomyolipomas arising in the anterior, central, and posterior mediastinum. It is the second report of an angiomyolipoma with chylothorax arising in the mediastinum and the third case with a history of a renal angiomyolipoma. In one patient, interruption of blood flow in the tumor was achieved by repeated arterial embolization after which the tumor became organized and diminished in size.³ Although renal angiomyolipomas are considered to be benign, some tumors may exhibit malignant features, including invasion of the renal vasculature and perirenal structures, regional nodal involvement, and local recurrence of retroperitoneal lymph nodes or organs not contiguous with the kidney. It is supposed that multicentricity of angiomyolipomas is caused by either the congenital presence of cell precursors in multiple sites or a form of benign metastases similar to that in benign metastasizing leiomyoma. In the present case, the mediastinal tumors were located in the posterior mediastinum and prepericardial and paraesophageal areas; furthermore, the patient's previous medical history included retroperitoneal tumor resection, and histopathological evaluation revealed that the mass was an angiomyolipoma. It can be concluded that extrarenal angiomyolipomas are caused by multicentricity rather than true metastasis.

 

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Table 1. Summary of all reported mediastinal angiomyolipomas

 

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