History
3-year-old girl with painless, slow growing «dermal»
tumour over distal third of left scapula.
Gross appearance:
Nodular soft tissue tumour, 4 x 3 x 2,5 cm with a white cut surface
and soft consistency.
Pathology
Partly encapsuled tumour consisting of fat cells with a focal
signet ring appearance and the typical morphology of lipoblasts.
There are also uniform stellate and spindled cells within a
myxoid matrix. The characteristic lobular pattern in this tumour
is not as prominent as expected in these lesions. In some areas,
the typical plexiform vascular network is obvious. Different
degrees of maturation can be seen in the various areas. No
cytological (nuclear) atypia is found.
Discussion
Lipoblastoma is a tumour of infancy. It is usually
noted during the first 3 years of life, and
occasionally at birth. It occurs most commonly in boys, as a
painless nodule or mass of the
upper or lower extremities. Two types have been described: circumscribed
(benign lipoblastoma) and diffuse (diffuse lipoblastomatosis).
The more common circumscribed form, located in the superficial
soft tissue, simulates a lipoma clinically.
The diffuse type tends to infiltrate not only the subcutis
but also the underlying muscle. Due
to its infiltrative potential, it shows a greater tendency to
recur. In most cases, the tumour grows slowly, but some lesions
can show a period of rapid growth. Radiologic studies
show a well demarcated soft tissue mass with the density of adipose
tissue. Neither CT nor MRI can reliably distinguish the lesion
from lipoma or liposarcoma.
Macroscopically, lipoblastoma is paler than
the ordinary lipoma, and its cut surface is
distinctly myxoid or gelatinous. Most tumours are 3-5cm in diameter.
Microscopy shows multiple irregular, well-defined,
paucicellular lobules composed of lipoblasts in different stages
of development, ranging from primitive, stellate and spindle
shaped mesenchymal cells (pre-adipocytes) to lipoblasts approaching
the univacuolar signet ring picture of the mature fat cell. The
degree of cellular differentiation may be the same throughout
the tumour or it may vary in the different tumour lobules
All human lipoblastomas reported to date have shown chromosomal
rearrangements involving the 8q11-13 region. PLAG1, a developmentally
regulated zinc finger gene, is the target protooncogene in lipoblastomas.
