대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Lipoblastoma with rupture

Radiologic Findings

Chest radiography shows a large mass and pleural effusion in right hemithorax with contralateral mediastinal shifting.

Precontrast chest CT scan shows a mass of 7 cm in diameter with areas of low attenuation (ranging -30 to 0 Hounsfield Unit). Postcontrast CT scan shows areas of inhomogenous contrast enhancement in the tumor component abuting the chest wall. Pleural effusion was observed in right upper hemithorax.

Gradient echo fast coronal MR image showed linear streaks and whorls of lower signal intensity arranged radially from the lateral chest wall, which corresponded with the area of contrast enhancement on CT scan. Pleural effusion was well demonstrated in right apical and posterlateral costophrenic region separeted by the mass.

Right thoracotomy with resection of the tumor was done. Yellow-whitish and myxoid material was found to leak from small tear of the well-encapsulated tumor. The mass was easily separated from the mediastinum, but tightly attached on the posterolateral aspect of the inner surface of the chest wall in the size of 4cm in range which was considered as the origin of the tumor.

Gross pathologic examination showed a well-encapsulated tumor composed of lipoblastomatous tissue with focal myxoid matrix. Intratumoral loose fibrovascular connective tissue were arranged radially from the the chest wall side of the tumor, which was well correlated with coronal MR images. The patient had immediate expansion of right lung and an uneventful postoperative course.

Brief Review

Lipoblastomas are rare benign mesenchymal tumors of embryonic white fat occurring in infancy and early childhood. Among the soft tissue tumors in the first year of life, it occupies only 3 % [1,2]. Approximately two thirds of them are found in the extremities [1, 2].
Occasionally the lipoblastoma arises in the neck, mediastinum, chest wall, and the retroperitoneal soft tissues. This tumor is well-encapsulated containing fetal-embryonal fat and loose fibrovascular connective tissue. The lipoblastoma arising from chest wall is rare and frequently has extrathoracic component [2, 3].

The tumor presents in two forms: a circumscribed lesion which is situated superficially (lipoblastoma) and a less common diffuse form which arises in deeper tissue (lipoblastomatosis) [1]. Histologically, the differentiation of lipoblastoma from liposarcoma, especially its myxoid variant, may be difficult. However, these benign immature adipocytic neoplasms have a more uniform growth pattern and typically show more striking lobulation.
Although lipoblasts in different stages of maturation are present in lipoblastoma, there is no nuclear atypia or pleomorphism, in contrast to that seen, at least focally, in liposarcoma [1].
In the younger patients, when they arises from the neck or mediastinum, these tumors can grow rapidly leading to recurrent respiratory infection or asphyxia, occasionally causing death if not removed [4].

Radiographically, lipoblastoma presents as a non-specific soft-tissue density mass.
CT allows identification of the fatty component and prominent intratumoral stranding, but may not allow differentiation between the various adipose tumors [3].
A case of lipoblastoma which was hypointense to fat on T1-weighted images and was of high signal intensity on T2-weighted image has also been described. This atypical MR manifestation was ascribed to the presence of an excessive amount of immature fat and myxoid tissue, intratumoral infarction, and extensive mucoid and cystic degeneration [2].
In the current case, MRI demonstrated a mass with areas of high signal intensity which was slightly lower than that of the subcutaneous fat on T-1 weighted image. Moreover, MRI suggested the chest wall origin of the tumor which was important for preoperative planning by the visualization of the tumor separating pleural effusion and intratumoral streaks and whorls radially arranged from the chest wall side of the tumor. This area of low signal intensity was corresponded well with the area of contrast enhancement on CT scan and the fibrovascular connective tissue on pathologic examination.

The main differential diagnosis is from a liposarcoma which may have an identical clinical and radiological presentation but is extremely rare in patients under 10 years of age [1]. Local recurrence following surgical excision of lipoblastoma is uncommon. Metastases have not been reported [4].

In current case, a large size of the tumor was notable at the age of 4 months, suggesting that it grew rapidly compressing the lung which caused severe respiratory distress. Additionally respiratory distress might have been attributed to pleural effusion associated with rupture of the tumor. Pleural effusion is an ancillary finding of ruptured teratoma [5]. Choi et al. described that pleural effusion was associated in 57% of the cases in ruptured teratoma [5]. We assumed that the pleural effusion in current case resulted from either spillage of internal components of a mass or from an inflammatory reaction to the extravasated contents.

References

1. Mentzel T, Calonje E, Fletcher (1993) Lipoblastoma and lipoblastomatosis: a clinicopathological study of 14 cases. Histopathology 23:527-533

2. Ko SF, Shieh C-S, Shih T-Y et al. (1998) Mediastinal lipoblastoma with intraspinal extension: MRI demonstration. Magn Reson Imaging 16:445-448

3. Cowling MG, Holmes SJ, Adam EJ (1995) Benign chest wall lipoblastoma of infancy producing underlying bone enlargement. Pediatr Radiol 25:54-55

4. Federici S, Cuoghi D, Sciutti R (1992) Benign mediastinal lipoblastoma in a 14-months-old infant. Pediatr Radiol 22:150-151

5. Choi SJ, Lee JS, Song KS, Lim TH (1998) Mediastinal teratoma: CT differentiation of ruptured and unruptured tumors. Am J Roentgenol 171:591-594

Keywords

Pleura, Malignant tumor,