Chapter 32: Tumors of Adipose Tissue, Muscle, Cartilage, and Bone

TUMORS OF ADIPOSE TISSUE

Tumors of adipose tissue are common in the skin and subcutaneous tissue (Table 32-1). Most are lipomas, but a number of other lesions have been described with distinctive clinical and pathologic features. Some of these have histologic features that overlap with liposarcoma. Although liposarcomas are more common in the deep soft tissues, any type of liposarcoma can occur superficially, albeit rarely. The prognosis for these tumors depends not only on histologic grade but also on clinical factors, such as anatomic site and patient age. Recently, characteristic cytogenetic abnormalities have been identified in many of these tumors.

Hamartomas

A hamartoma is a focal malformation composed of tissue elements normally found at that site, arranged in a disorganized manner. They occur in many different parts of the body, including the skin, and are most often asymptomatic. Hamartomas are benign, but they can create cosmetic issues for patients.

Focal dermal hypoplasia

Clinical and Histopathologic Features

Focal dermal hypoplasia (Goltz syndrome) is an X-linked dominant multisystem birth defect affecting tissues of ectodermal and mesodermal origin.¹ It results from mutations in the PORCN gene, which disrupts Wnt signaling.² Anomalies may involve the skin, skeleton, eyes, and face.¹ It is more common in girls. Skin findings at birth include patches of atrophic or even absent skin, pigmentary changes, or yellow to red nodules in a reticular pattern. Histologically, the dermis is underdeveloped and replaced by mature adipose tissue.³ The surrounding dermal collagen fibers may be smaller than normal.

Differential Diagnosis

The differential diagnosis includes nevus lipomatosus, which also exhibits mature adipose tissue in the dermis, but it occurs in adults and is not associated with other defects, and the surrounding dermal collagen is normal.

Nevus lipomatosus

Clinical Features

Nevus lipomatosus presents mainly as: (1) fleshy to yellowish papules, plaques, and/or nodules with a predilection for the lower trunk of newborns and young people, or (2) a solitary lesion occurring anywhere at any age (overlapping with, and possibly identical to, skin tags).^4-6 Multiple lesions may coalesce into plaques with a cerebriform surface up to 10 cm in diameter.

Histopathologic Features

Histologically, variable amounts of mature adipose tissue are ...