Congenital Smooth Muscle Hamartoma

 Haphazard arrangement

image Thin fascicles rather than solid growth pattern

image No atypia

image No mitoses

image No necrosis

image Immunohistochemistry (+) for muscle markers

Top Differential Diagnoses

• Cutaneous leiomyoma (pilar leiomyoma)
image Occurs in adults

image Different anatomic distribution

image Lobules of mature smooth muscle

• Leiomyosarcoma
image Adults

image Deeply infiltrative dermal and subcutaneous tumor

image Cytologic atypia

image Mitotic activity

• Neurofibroma
image Wavy nuclei

image Myxocollagenous stroma

image S100(+)

• Normal skin from special sites
image Nipple and genital skin

Smooth Muscle Hamartoma: Low Power
Congenital smooth muscle hamartoma shows a haphazard arrangement of smooth muscle bundles image present throughout the dermis.

Smooth Muscle Hamartoma: Medium Power
Medium-power view of congenital smooth muscle hamartoma shows a disorganized proliferation of smooth muscle bundles image present in the dermis.

Smooth Muscle Hamartoma Surrounding Adnexal Structures
Higher magnification shows the numerous bundles of smooth muscle. The smooth muscle bundles resemble arrector pili muscles but are present in a greater density than normal arrector pili muscles image. In this case, they infiltrate around eccrine units.

Smooth Muscle Hamartoma: High Magnification of Smooth Muscle Bundles
High magnification shows a fascicular arrangement of smooth muscle with characteristic elongated, spindle-shaped to blunt-ended nuclei image.



• Smooth muscle hamartoma


• Rare, benign smooth muscle tumor presenting in infants

• Characterized by disorganized proliferation of smooth muscle bundles

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Congenital Smooth Muscle Hamartoma

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