Author: Yigiter, Murat
Date published: September 1, 2010
Lipoblastomas are benign soft tissue tumors originating from white embryonic fat1'2. They are classified into two forms: benign lipoblastomas are localized, capsular and well-circumscribed tumors, while benign lipoblastomatosis is the occurrence of deeply embedded, noncapsulating, multicentric, and infiltrative tumors3"5. These tumors typically occur before three years of age and usually develop in the extremities6-7. However, chest wall involvement has been reported rarely. The tumor can behave in a locally aggressive manner and invade the surrounding tissues. In spite of its local invasion and rapid growth properties, it is not considered malignant1'2. Treatment of lipoblastoma consists of surgical excision and a close follow-up period of two to five years3. In this report, we discuss the rare occurrence of chest wall lipoblastomatosis in children and briefly review the English literature of this rare tumor.
A two-year-old girl was admitted to our clinic with a rapidly growing mass on the right side of the chest wall first noticed by her parents a month earlier. Past medical history was unremarkable. Physical examination revealed a nontender, irregular, firm, and fixed mass measuring 3x2 cm over the right hemithorax approximately 1-2 cm lateral to the right areola. The remainder of the physical examination was unremarkable. Serum chemistry, complete blood count, human chorionic gonadotropin, alpha-fetoprotein, and carcinoembryogenic antigen levels were within normal limits. The posteroanterior and right lateral chest radiographs demonstrated a 4x5 cm opacity on the right anterior hemithorax. A computerized axial tomography scan of the chest showed a soft- tissue mass measuring 5x3x6 cm with irregular demarcated borders, including adipose tissue components. The mass occupied the anterior part of the right thoracic cage between ribs 7 to 11, anteriorly compressing the middle pulmonary lobe, inferiorly compressing the anterior right lobe of the liver and extending to the anterolateral chest wall through the intercostal muscles (Fig. 1). An abdominal computerized tomography scan was normal.
Fine needle aspiration biopsy revealed no specific diagnosis or atypical cells. Planned surgical resection was made to accomplish both diagnostic and treatment goals. At thoracotomy, a multilobulated, irregular and encapsulated firm fatty mass was seen arising from the anterior chest wall and protruding into the right thoracic cavity (Fig. 2). Frozen section examination revealed an adipose tumor with no atypical cells. A complete excision of the mass was achieved successfully without resection of the chest wall. Results of the histological examination of the specimen revealed lobules of mature and immature adipose tissue, separated by well-vascularized fibrous septa. Myxoid stroma was present, and fatty cells showed a spectrum of maturation from primitive stellate cells to spindle cells (Fig. 3). Extension of the lesion to striated muscle tissues was observed in some areas; therefore, a diagnosis of lipoblastomatosis was made. The postoperative course was uneventful and the patient was symptom-free with no evidence of recurrences during the one-year period after the operation.
Lipoblastoma, which was originally described in 1973 by Chung and Enzinger6, is a rare benign mesenchymal tumor of adipose tissue. Although the exact etiology of lipoblastoma is unknown, immunohistochemical and ultrastructural studies demonstrated that lipoblastoma was related with continued proliferation of immature embryonic white fat cells and lobules in the postnatal period2-8-9. Clinicopathologically, there are two forms of lipoblastoma: the well-circumscribed, capsular and localized type is called benign lipoblastoma, and the deeply embedded, irregularly confined and noncapsulating type with the tendency to an infiltrative growth is called lipoblastomatosis1-3-5. Both forms usually occur in infants and young children and have a male preponderance, with a varying sex ratio2-7. However, four male and six female (including the current case) patients affected by chest wall lipoblastomas have been reported (Table I) 1^5-7-10-14. Although they may arise almost anywhere within soft tissue, the trunk and extremities are the most common sites. The head and neck region, mediastinum and retroperitoneum have been reported rarely15-17. Chest wall involvement is also extremely uncommon. We could find only nine cases of thoracic wall lipoblastoma with four prior cases of lipoblastomatosis1-2'5'7'10"14. Lipoblastoma/ lipoblastomatosis usually exhibits as a painless mass. However, some patients are symptomatic at the time of initial diagnosis because the rapidly growing mass causes compression effects on surrounding structures3-17. Our patient exhibited a rapidly growing but painless mass on the chest wall.
These tumors are macroscopically lobulated and soft. Histologically, lobules of mature and immature fat cells are found, including varying degrees of differentiation from primitive stellate cells to spindle cells. Lobules are separated by fibrous septa containing vessels, collagen and fibroblasts2-3-18. The diffuse form may differentiate from lipoblastoma with a less pronounced lobular pattern and an infiltrative growth pattern indicated by skeletal muscle fibers2.
The differential diagnosis of lipoblastoma includes lipoma, hibernoma and myxoid or well-differentiated liposarcomas2-5-13. Histologic examination is almost always definitive. Lipomas are less cellular than lipoblastoma and lack lipoblasts, whereas hibernomas consist almost entirely of brown fat cells with mitochondriarich, eosinophilic, granular cytoplasm2-5. However, the most important differential diagnostic consideration is myxoid liposarcoma because of the presence of lipoblasts and the plexiform vascular pattern in a myxoid background. The patient's age and histologic appearance are fundamental to distinguish lipoblastoma from myxoid liposarcoma. Younger patients, the lobulation and the absence of the pleomorphic and atypical cells with abnormal mitoses are more strongly correlated with lipoblastomas1-5-10. Histologically, borderline lesions may be differentiated with cytogenetic analysis. Characteristically, lipoblastomas have rearrangements in the long arm of chromosome 8 (8qll-13), affecting PLAGI, whereas a distinctive translocation t(12;16)(ql3;pll) is observed in myxoid liposarcoma2- 19-20. Nevertheless, despite the frequent presence of chromosome 8 anomalies, lipoblastomas may fail to show a karyotypic aberration. For this reason, the indication to perform cytogenetics was not specified. However, if the pathologist is unable to differentiate between lipoblastoma and myxoid liposarcoma, cytogenetic investigations should be performed. A brief summary of the chest wall lipoblastomas including results of cytogenetic analysis is presented in Table I. Because we resected the mass completely and lipoblasts were observed in all developmental stages on the pathologic examination, we had no doubt regarding the diagnosis.
Radiological studies may be helpful in the differential diagnosis of soft tissue tumors, but are usually not reliable in differentiating between the different lipomatous tumors. There are no known imaging findings associated with lipoblastoma; therefore, imaging is best used for surgical planning and postoperative surveillance rather than for diagnosis3-19.
In spite of their potential for local invasion and rapid growth, lipoblastomas have an excellent prognosis with no report of any distant metastases. The surgical excision is usually curative if the tumor is removed completely11'21. Therefore, the treatment of lipoblastoma must be surgical excision with negative margins except for large invasive lesions requiring mutilating resection2-3'19. In the chest wall lesions reviewed, only two reports revealed a chest wall excision including ribs 7 to 9 together with the parietal pleura1'14. In our patient, intra- and extrathoracic components of the tumor could be removed completely, avoiding potentially disfiguring procedures. When incompletely resected lesions exist, close clinical follow-up to monitor progression with various imaging methods is advised. All patients should have careful surveillance and a follow-up period of at least five years in light of the documented recurrence rate of these lesions3-10. Appropriate length of follow-up is controversial because there is a report of a recurrence seven years after the primary tumor removal10. In this respect, we planned a close follow-up with both clinical examinations and regular radiologic tests with ultrasonography over a five-year period. On the other hand, magnetic resonance imaging can be helpful to monitor size/progression in patients with multiple recurrences or incomplete tumor resections.
In conclusion, benign lipoblastomatosis differs from other benign pediatric lipomatous tumors due to the reported recurrence rate of these tumors. However, lipoblastoma has no risk of metastasis. The goal is complete resection of the tumor with negative margins though this is not always possible. We think that this is a benign tumor and that radical cancer surgery should be avoided even in cases where the tumor was not completely removed.
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Murat Yigiter1, Ibrahim Ötgün1, Halil Kiyici2, Ibrahim Akkoyun3, Selçuk Yücesan1, Akgün Hicsönmez1
Departments of 1 Pediatric Surgery, and 2 Pathology, Baskent University Faculty of Medicine, Ankara, and 3 Department of Pediatric Surgery, Numune State Hospital, Konya, Turkey