Idiopathic Spontaneous Occurrence of Heterotrophic Occurrence During Pregnancy

Abstract

Heterotopic ossification (HO) typically presents in the hip, knee, and elbow joints in the setting of trauma or postsurgical intervention. Less commonly, it may occur secondary to neurologic dysfunction or underlying genetic conditions, but idiopathic HO is rare. Most cases of HO are managed nonoperatively with surgical resection remaining a controversy due to high recurrence rates. We describe a case of idiopathic HO of the shoulder that occurred in the absence of trauma, neurologic dysfunction, or underlying genetic disorder that was treated with surgical excision. Heterotopic ossification (HO) is the formation of ectopic bone within the soft tissues. 1 HO can be classified into three broad categories based on etiology: traumatic HO from fractures, dislocations, orthopaedic surgeries, and burns; neurogenic HO from spinal cord damage or head injury; and genetic HO from conditions, such as progressive fibrodysplasia ossificans or progressive osseous heteroplasia. 2 Traumatic HO comprises up to 90% of cases, most commonly a complication of arthroplasty or bone fracture, with a higher predisposition for men. 3 Although it can occur anywhere in the body, HO typically affects areas most susceptible to trauma, such as the elbow, thigh, pelvis, and shoulder. 4 When symptomatic, HO can present with pain, decreased range of motion, and in severe cases, bony ankylosis. 2 The diagnosis is made with radiographic imaging, including radiographs, CT, and MRI. Several classification systems have been used to grade the severity of HO, but the Brooker Classification System used for HO at the hip 5 and the Hastings and Graham System for HO at the elbow 6 are two of the most commonly used.A definitive diagnosis of HO can be made by histopathologic evaluation of a tissue sample. HO is often defined pathologically by the type of tissue in which it occurs, such as myositis ossificans involving skeletal muscle. The histopathologic features of the lesion typically evolve over time, with early lesions being composed of cellular fibrovascular tissue with small amounts of bone matrix. More mature lesions have prominent bone formation with a zonal architecture, a hallmark of HO. It is important to differentiate HO from a neoplastic process, such as soft-tissue sarcoma or osteosarcoma. Microscopically, in more mature lesions, trabeculae of woven bone with osteoblastic rimming accompanied by more mature lamellar bone is more