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Miscellaneous Remnants and Neoplasms


29.1

Nevus lipomatosus

(see Fig. 29.1 )

Fig. 29.1, Nevus lipomatosus.

Rare clustered papules or nodules of the buttock with onset at birth or childhood.

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    Adipose present in superficial dermis

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    Increased dermal blood vessels often

Differential diagnosis

  • 1.

    Lipofibroma variant of acrochordon (27.4): much more common, adult onset, usually solitary, pedunculated nodule with a narrower base. Many doctors misname these large tags “nevus lipomatosus” by mistake.

  • 2.

    Goltz syndrome (11.8): nearly no dermis, clinical features much different.

  • 3.

    Piezogenic pedal papules (29.1): papules on the heels , occasionally painful (1.96), thought to be pressure-induced herniations of adipose through an atrophic or secondarily thickened dermis.

  • 4.

    Adipose may also be found superficially in the dermis in Proteus syndrome, Michelin tire baby, lipedematous alopecia (10.13), some lipomas (29.2), some melanocytic nevi (nevus lipomatosus et pigmentosus; 20.5), and healed old wounds.

29.2

Lipoma

(see Fig. 29.2A–E )

Fig. 29.2, A Angiolipoma (low mag.).

Fig. 29.2, B Angiolipoma (medium mag.).

Fig. 29.2, C Spindle cell lipoma.

Fig. 29.2, D Pleomorphic lipoma.

Fig. 29.2, E Infiltrating lipoma.

Very common soft subcutaneous (1.135) nodules.

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    Proliferation of normal-appearing adipose in the subcutaneous fat

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    Sometimes sharp demarcation (rarely a capsule) from normal adipose

Variations

  • 1.

    Angiolipoma: many small blood vessels , often thrombi (1.137), more likely to be well circumscribed and painful (1.96).

  • 2.

    Fibrolipoma: increased fibrous tissue.

  • 3.

    Spindle cell lipoma: usually on posterior neck (1.86) or upper back, more in males, CD34 + spindle cells (1.131) in mucinous stroma (1.83), increased collagen and mast cells (1.78).

  • 4.

    Pleomorphic lipoma: usually on posterior neck (1.86), hyperchromatic adipocytes, bizarre floret giant cells (1.84) that have overlapping nuclei, a pseudomalignancy (1.118), resembles liposarcoma but only has rare lipoblasts and has no necrosis.

  • 5.

    Infiltrating lipoma (intramuscular lipoma): skeletal muscle trapped between mature adipocytes.

  • 6.

    Chondroid lipoma: rare, encapsulated, chondroblasts and lipoblast-like cells, myxoid stroma, S-100 + in cartilaginous areas, may resemble hibernoma (29.4), myxoid liposarcoma (29.5), or extraskeletal chondrosarcoma.

  • 7.

    Myolipoma: well-circumscribed subcutaneous nodule, mostly smooth muscle positive for actin and desmin, with about one-third adipose.

  • 8.

    Angiomyolipoma: probably is a variant of angioleiomyoma (29.6) with fatty metaplasia. The angiomyolipoma of the kidney is associated with tuberous sclerosis (27.3), but is somewhat different and probably not related to the subcutaneous lesions.

  • 9.

    Dercum’s disease (adiposis dolorosa): multiple painful lipomas (1.96), usually with ordinary histology or angiolipoma.

  • 10.

    Multiple symmetric lipomatosis (Madelung’s disease): multiple diffuse lipomas, mostly in males, often in a horse collar distribution.

Differential diagnosis

  • 1.

    Liposarcoma (29.5): large size, lipoblasts , and cytologic atypia.

29.3

Benign lipoblastoma

Rare subcutaneous nodule or mass in young children , more common in males. Lesions may recur after excision, but do not metastasize.

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    Subcutaneous tumor (poorly circumscribed or encapsulated) of immature fat cells with lipoblasts (lipid vacuoles displace the nuclei)

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    Mucinous stroma (1.83)

Differential diagnosis

  • 1.

    Liposarcoma (29.5): histologically almost identical, but occurs in adults, with more cytologic atypia.

29.4

Hibernoma

(see Fig. 29.4 )

Fig. 29.4, Hibernoma.

Very rare benign lipoma of immature brown fat in adults. It grows slowly, and is most common on the neck (1.86), upper back , and axilla (1.10).

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    Subcutaneous encapsulated tumor of mulberry cells (large cells with a central nucleus and multivacuolated granular cytoplasm), sometimes mixed with mature adipocytes

Differential diagnosis

  • 1.

    Lesions with foam cells (1.46) or clear cells (1.22), such as foamy macrophages related to fat necrosis in panniculitis (1.101) are rarely confused with a hibernoma.

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