Presented by: Jaryd Freedman, MD, and Mark Abdelmalek, MD
Drexel University College of Medicine
May 16, 2014
Osteoma cutis (OC) is a subtype of heterotopic bone formation in which foci of bone develop in the skin. This uncommon entity is traditionally classified as either primary or secondary. While both forms are uncommon, secondary OC is more common than primary OC accounting for 75-85% of cases.
In primary OC, foci of bone develop in the absence of an associated skin lesion. There are five syndromes associated with primary OC: fibrodysplasia ossificans progressiva, progressive osseous heteroplasia, Albright hereditary osteodystrophy, plate-like osteoma, and multiple miliary osteoma cutis.
In secondary OC, bone develops within a preexisting skin lesion. Secondary OC, also known as metaplastic ossification, has been reported to occur secondary to traumatic lesions, scars, connective tissue diseases, nephrogenic systemic fibrosis, and benign and malignant neoplasms including nevi (termed nevus of Nanta), basal cell carcinomas, squamous cell carcinomas, pilomatricomas, trichoepitheliomas, dermatofibromas, lipomas, and organoid nevi.
Secondary OC typically develops through intramembranous bone formation. While the pathogenesis has yet to be elucidated, recent literature points to inappropriate cell signaling leading to mesenchymal stem cells developing into bone-forming cells. On histopathology, there are large spicules of bone present in the reticular dermis or subcutaneous tissue in association with a primary lesion. Often cement lines and a primitive haversian system can be seen. Occasionally osteoblastic activity can be seen, however osteoclasts are uncommon. Rarely hematopoietic stem cells can be seen within the osteoma.
OC in association with a split-thickness skin graft has yet to be reported in the literature. However, there are many reports of osteomas occurring within abdominal surgical scars. These are most often associated with abdominal scars near the xyphoid process or pubic bone. Thus, it has been hypothesized that the etiology of abdominal scar osteoma involves seeding of the scar with osteoblasts from these bones into the wound. The literature regarding abdominal scars with osteomas suggests that OC in scars is a harmless incidental finding. OC may be a contributing factor to chronic ulcerations.
Further research regarding the role of osteoma cutis in preventing the healing of chronic wounds is needed. Potential mechanisms may involve mechanical inhibition of reepithelialization, providing foci for bacterial colonization, or promoting a cytokine milieu which inhibits healing.
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