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Abstract: Ossification is uncommon, generally asymptomatic, and often incidentally identified in imaging studies. We report on a 54-year-old man who participated as a healthy volunteer in a clinical trial using PET imaging to investigate neuroinflammation. An incidental ossified lesion in the anterior falx cerebri was revealed by MRI. CT scan showed a small hypodense center in the lesion, probably corresponding to bone marrow. The PET scans using 18 F-SF51, 11 C-PS13, and 11 C-MC1 showed increased uptake within this lesion, which was probably related to bone marrow activity within the ossification., Competing Interests: Conflicts of interest and sources of funding: This study was funded by the Intramural Research Program of the National Institute of Mental Health, National Institutes of Health (projects ZIAMH002852 and ZIAMH002793). The authors have no potential conflicts of interest to disclose, financial, or otherwise., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Heterotopic ossification (HO) is a benign condition characterized by the abnormal formation of mature lamellar bone in extraskeletal soft tissues. Most frequently, HO is observed around the hip joint after fractures or surgical procedures such as open reduction internal fixation or total hip arthroplasties. We are presenting a case of HO as detected by F-NaF PET/CT in a 68-year-old woman with multiple myeloma and a history of internal fixation of the right hip. Many previous publications have reported F-NaF uptake portraying calcification in soft tissue; the present report demonstrates the feasibility of F-NaF PET/CT to assess extraosseous calcification.

Heterotopic ossification is a rare phenomenon that refers to formation of bone outside the skeletal system. We present a 61-year-old woman who suffered from peritoneal cancer surgery 2 years ago, referred for Tc-MDP bone scan because of higher serum CA-125 level, which showed multiple intense tracer activities in her abdominal and pelvic region without other abnormalities. SPECT/CT revealed the activities were loaded in the intestine but not in the bone. A wait-and-see policy was adopted because of no abdominal discomfort. After 1-year follow-up, another bone scintigraphy showed the tracer uptake was significantly decreased.

A 29-year-old male patient suffered from paraplegia 6 months after brain injury. Heterotopic ossification was diagnosed based on clinical characteristics such as decreased range of motion at the bilateral hips without infective signs. A planar bone scintigraphy using Tc-MDP showed intensive radiotracer accumulation in the proximal portion of the bilateral femurs and the right acetabulum. The SPECT/CT images showed increased radiotracer accumulation in the adjacent soft tissues of the bilateral hips but not in the bone. The conservative treatment rather than surgical intervention was given according to the findings in bone SPECT/CT images.

A 55-year-old man developed bilateral hip pain following admission with Guillain Barre syndrome. Hip radiographs showed minor degenerative changes. 99mTc-methylene diphosphonate bone scintigraphy showed bilateral abnormal activity extending from the acetabula to the trochanteric regions. SPECT/CT localized the abnormal activity to the soft tissues surrounding the hips. Heterotopic ossification is a rare complication of Guillain Barre syndrome.

A 46-year-old man, with a history of bilateral amputations, presented with a long-standing chronic nonhealing wound at the left below-knee amputation, which was sustained after a crush injury. The patient was referred for a bone scan to exclude osteomyelitis of the left stump. The bone scan showed increased uptake in the left below-knee amputation stump, raising the possibility of an infection. However, SPECT/CT of this area confirmed the uptake to correspond to the heterotrophic ossification of the left below-knee stump and no evidence of osteomyelitis.

A CT scan of a 69-year-old male patient, performed for staging of suspected lung carcinoma, incidentally showed an irregular lesion of 10 cm in the upper abdomen. Further investigation using FDG-PET showed only moderately increased glucose metabolism, whereas Tc-99m MDP SPECT revealed intense osteoblastic activity inside the lesion. A CT-guided biopsy was performed and histologic analysis established the diagnosis of heterotopic mesenteric ossification. This pathology is rare and mostly diagnosed when it is complicated by small bowel obstruction.

Heterotopic ossification is a disorder of unknown etiology characterized by bone formation in the mesenchymal tissues. It occurs most commonly in patients who have had traumatic brain injury, spinal cord injury, or joint trauma or surgery.

Heterotopic bone in the left femoral head area showed progressive decrease in Tc-99m MDP uptake, only to reveal increased uptake at a later date.

Diffuse pulmonary ossification (DPO) is a rare pathologic finding of heterotropic bone formation within the lungs. It has been associated with mitral stenosis, chronic left ventricular failure, interstitial fibrosis, metastatic breast cancer, pulmonary amyloidosis, histoplasmosis, and chronic busulfan therapy. This patient represents a case associated with Placidyl use.

Two cases of increased scintigraphic activity in a persistent transverse process epiphysis are presented to illustrate the need to recognize this as a normal developmental variant. Differentiation from fracture or neoplasm usually can be made by correlative radiographic imaging.

The extensive heterotopic bone formation in patients with fibrodysplasia ossificans progressiva (FOP) has been documented previously with radiographs. A case in which a Tc-99m MDP bone scan showed increased uptake at sites well before ossification could be documented radiographically is described. This finding suggests that bone scans would likely be useful to monitor the extent of involvement with FOP and to detect areas of new activity.

The typical appearance of subcutaneous ossification on a single photon emission computed tomography (SPECT) bone image is reminiscent of the patterns discovered by radiographs and computerized tomography. A case demonstrates the advantage of SPECT imaging to clarify the actual location of soft tissue Tc-99m methylene diphosphonate in this condition.