Heterotropic Ossification

CLINICAL HISTORY

A newborn infant was hospitalized with complications related to a congenital heart disorder. On the day of birth, intravenous access was obtained through a peripheral vein on the dorsum of her foot. Infiltration of this IV occurred after one day, resulting in localized soft-tissue swelling and erythema. The IV was removed two days after placement. Two weeks later, a hard, palpable softtissue mass was noted at the same location on the dorsum of the foot. The mass was tender and continued to enlarge. Imaging studies of the foot were obtained three weeks after the initial IV placement.

FINDINGS

Radiographic studies of the foot were performed. An amorphous soft-tissue mass with mineralization on the dorsum of the foot is seen on the initial radiograph (Figure 1). The disease process does not appear to involve the underlying bones of the foot. After one month, repeat radiographs demonstrate evolution of the process, with enlargement of the mass and peripheral mineralization (Figure 2). A CT scan of the foot confirms the mass to be mostly mature at the periphery with less ossification at the center and soft tissue separating the lesion from the adjacent cortex (Figure 3). After eight weeks of conservative treatment, repeat radiographs demonstrate interval shrinkage and dissolution of the mass (Figure 4).

DIAGNOSIS

Heterotopic ossification.

DISCUSSION

Heterotopic ossification refers to the formation of lamellar bone within soft tissues secondary to genetic, traumatic, or iatrogenic causes. It can present as small, clinically insignificant flecks of bone or large deposits of ossification. The condition’s initial radiographic appearance can be confused with metastatic calcification in hypercalcemic disorders or more worrisome entities such as parosteal osteosarcoma or juxtacortical chondroma.

The pathogenesis for heterotopic bone formation is not fully understood. Though there are inherited disorders, such as fibrodysplasia ossificans progressiva and progressive osseous heteroplasia, that are associated with advanced and often disfiguring manifestations of heterotopic ossification, these disorders are rare and tend to arise from spontaneous mutations.

The disorder is seldom seen in infants, and heterotopic ossification in children most frequently presents secondary to inheritable causes. The forms of the disease most commonly encountered clinically in the nonpediatric age group are neurogenic and post-traumatic, with bone morphogenetic proteins elicited from the site of soft-tissue injury playing a key role in the reactive ossification process.

Treatment ranges from conservative therapy with spontaneous resolution to bisphosphonates and radiation for more advanced cases.

Condensed from, An unusual complication of an infiltrated intravenous catheter: heterotopic ossification in a newborn. Journal of Radiology Case Reports (online journal), 2008;2(2):13-15. The full case can be reviewed online at www.radiologycases.com/index.php/radiologycases/article/view/30/22. Contributing authors Dr. Lavi Nissim and Dr. Dorothy Gilbertson-Dahdal are affiliated with the University of Arizona radiology department in Tucson.

BIBLIOGRAPHY

Kaplan FS, Glaser DL, Hebela N. Heterotopic ossification. J Am Acad Orthop Surg 2004;12(2):116-125.
Kaplan FS, Xu M, Glaser DL, et al. Early diagnosis of fibrodysplasia ossificans progressiva. Pediatrics 2008;121(5):e1295-1300.
McCarthy EF, Sundaram M. Heterotopic ossification: a review. Skeletal Radiology 2005;34(10):609-619. Vanden Bossche L, Vanderstraeten G. Heterotopic ossification: a review. J Rehabil Med 2005;37(3):129-136.