Lipoma

Variant: Myolipoma (Lipoleiomyoma)

Composed of mature fat and bland smooth muscle
- Muscle predominates in most cases
  - Usually evenly interspersed
  - Focal smooth muscle overgrowth in one reported case
  - Muscle in short fascicles
- Both components lack any atypical features
  - No cytologic atypia or lipoblasts
  - No floret cells
  - No mitotic figures
  - No necrosis
Stroma may be sclerotic or hyalinized
- Occasionally myxoid
- No prominent vascular component

Angiomyolipoma	Myolipoma
Abnormal large vessels	No abnormal vascular component
Epithelioid perivascular cells	No epithelioid component
HMB45, MelanA positive	HMB45, MelanA not reported

Atypical Lipomatous Tumor with Smooth Muscle Metaplasia	Myolipoma
Atypical cells present	No atypical cells
Fibrous septa frequent	Fibrous septa absent
Floret cells or lipoblasts frequent	No floret cells or lipoblasts

Spindle Cell Lipoma	Myolipoma
Restricted to back of neck, upper back, shoulders	Predominantly pelvic
Scant cytoplasm	Tapered cytoplasm in spindle cells
CD34 positive	CD34 negative
Actin positive	Actin negative

Low Grade Leiomyosarcoma Infiltrating Fat	Myolipoma
Fat is overrun (asymmetrically involved)	Fat is integral to lesion (throughout)
May have atypia, mitotic figures	No atypia or mitotic figures

Rarely reported
Age 28-73
Sites of involvement
- Females: pelvic, retroperitoneal, suprapubic,inguinal
- Males: inguinal, abdominal wall, back
- Other sites include eyelid, spinal cord and pericardium
No known association with tuberous sclerosis
No recurrences reported (limited followup)

Takahashi Y, Imamura T, Irie H, Tanaka F, Fukushima J, Fukusato T, Harasawa A, Shiga J. Myolipoma of the retroperitoneum. Pathol Int. 2004 Jun;54(6):460-3.
Guillou L, Coindre JM. Newly described adipocytic lesions. Semin Diagn Pathol. 2001 Nov;18(4):238-49.
Michal M. Retroperitoneal myolipoma. A tumour mimicking retroperitoneal angiomyolipoma and liposarcoma with myosarcomatous differentiation. Histopathology. 1994 Jul;25(1):86-8.
Meis JM, Enzinger FM. Myolipoma of soft tissue. Am J Surg Pathol. 1991 Feb;15(2):121-5.