Lipoblastoma – A Rare Benign Immature Adipocytic Neoplasm
Lipoblastoma is an extremely uncommon mesenchymal soft tissue tumor affecting infants and toddlers. It is a fat-containing tumor and is usually well encapsulated. When it is diffusely infiltrative, it is termed as lipoblastomatosis. This tumor is benign in nature, however, is locally aggressive and can present with post-surgical recurrence. Symptoms may vary depending on the site which is affected. It is usually a painless, progressively increasing swelling, and predominantly affecting the extremities. Here, we present a case of an infant presenting with painless fat- attenuation swelling of the neck with soft tissue septations within.
A 1-year-old male child presented with painless swelling on the left side of neck for 3 months, progressively increasing in size.
On clinical examination, a diffuse swelling was noted on the left side of neck, which was compressible. No bruit or pulsations noted. No signs of inflammation were seen in the overlying skin.
Contrast-enhanced computed tomography revealed a well-defined mass lesion in the posterior triangle of the left side of neck insinuating into the left axilla, measuring 10 cm×8 cm×6 cm [Figures 1-4]. The lesion had predominant fat attenuation, along with enhancing septations and soft tissue. No calcification or fluid attenuation was seen. Cranially, the mass started from C2 vertebral level and extended into the left axilla until the level of sixth rib. There was mass effect on the chest wall in the form of inward bowing of the ribs but no intrathoracic extension. The mass was causing anteromedial displacement of internal jugular vein and common carotid artery. The left subclavian artery is seen to drape around the mass. However, fat planes with the vessels and adjacent structures are well maintained. Imaging findings were characteristic of lipoblastoma. The child was managed surgically and the tumor was resected completely.
Lipoblastoma is a rare mesenchymal soft tissue tumor of early childhood, (<3 years) of age with predilection for male infants. The tumor is benign in nature, however, may be locally invasive or progressive. Lipoblastoma term is used when it is well-defined and encapsulated, as in our case whereas when diffusely infiltrative, it is called lipoblastomatosis. The former is seen in subcutaneous region whereas the latter affects the underlying muscles as well. Lipoblastoma is commoner than lipoblastomatosis, occurring most commonly in the extremities (70% cases) followed by chest and head and neck region. Since it is a tumor of embryonal white fat, histologically cells range in differentiation from prelipoblasts to mature lipocytes interspersed in a myxoid stroma. These tumors are locally aggressive; however, metastasis is not known to occur.
The classical CT appearance of the tumor is that of a fat attenuation soft tissue mass which can be well encapsulated (as in lipoblastoma) or can be insinuating having ill-defined margins (as in lipoblastomatosis) with presence of multiple thin enhancing septation within. However, the appearance would vary depending upon the relative ratio of adipose tissue and soft tissue elements. No calcification or cystic changes are noted within the mass. Few smaller areas of necrosis, however, may be seen. The imaging appearance of lipoblastoma is indistinguishable from that of liposarcoma; however, liposarcoma is extremely rare in an age group of <10 years; hence, despite large soft tissue component in such a fat-containing mass in this age group is almost always a lipoblastoma.
The main differential diagnosis for this tumor is dermoid (which can be differentiated due to presence of calcification), lipoma (relevant history of stagnant growth of tumor) and liposarcoma (occurs in elderly).
The clinical presentation of progressively increasing soft tissue swelling in extremities or head-neck region in a small child mandates exclusion of rhabdomyosarcoma, which is aptly achieved by CT or magnetic resonance imaging by the demonstration of fat.
Take home message from this case report is that a fat- containing mass in early childhood is usually lipoblastoma. While myxoid component is common in lipoblastoma presenting in infancy, adipose component predominates later. CT appearance and histology of lipoblastoma overlap with myxoid liposarcoma; however, latter is rare in childhood.