Radiology Teaching Files > Case 1796932

Contributed by: Faculty and residents Children's Hospital, Radiologist, Children's Health System, Birmingham, Alabama., USA.
Patient: 3 year old male
History: Acute onset of left hip pain in an afebrile 3 year old male with normal WBC and slightly elevated CRP and Sed rate who is not improving despite multiple IV antibotics. Patient had a negative needle biopsy 4 days after admission.

Fig. 1: Presenting hip radiograph

Fig. 2: Axial T2

Fig. 3: Coronal T1 with contrast

Fig. 4: Axial T1

Fig. 5: Axial CT with contrast

Fig. 6: Coronal CT with contrast

Fig. 7: CT scout

Radiograph of the pelvis obtained at admission shows loss of gluteal fat pads and soft tissue swelling of the left hip flexor muscles. No joint space widening or soft tissue califications are seen.

MRI obtained 4 days later demostrates decrease T1, increase T2 and FLAIR signals involving the flexor muscles and iliacus of the left hip. Post Gad images demostrate diffuse enhancement of the same muscles. No fluid collection, focal enchancing mass, abnormal marrow signal or cortical destruction is seen.

CT 14 days later demostrates low attenuation of the left hip flexor/iliacus muscles with an irregular mildly enhancing soft tissue mass. Discontinous perphireal califications are seen on both CT and scout image.

Diagnosis: Myositis ossificans either primary, or secondary to needle biopsy of questionable pyomyositis.

Myositis ossificans occurs in 2 forms: Myositis ossificans circumscripta / traumatica (secondary to soft tissue injury or without known injury) and Myositis ossificans progressiva (an autosomal dominant genetic disorder with complete penetrance and variable expression).

Nonhereditary myositis ossificans
* Rare in children < 10 yoa
* Pain, tenderness, focal swelling, fever (rare)
* History of trauma may be difficult to elicit.
* 80% ossifications occur in the thigh or arm
* ESR and WBC count are rarely elevated.
* Progressiva: Short metacarpals and metatarsals, vertebral anomalies, increased incidence of enchondromas
* Early examination may be unremarkable.
* CT scan shows fascial plane edema before ossification occurs.
* Floccular calcified mass at 2-6 weeks from onset.
* AT 6-8 weeks, calcification becomes sharply circumscribed.
* MRI early shows low T1 signal and high T2 intensity (edema). Late imaging shows peripheral rim of low intensity on all sequences. Irregular areas of increase T2 signal then central signal intensity similar to fat on all sequences with areas of low signal due to ossification.
* Biopsy may be performed to exclude osteosarcoma.
* Surgery only for nonhereditary myositis ossificans and only after maturation of the lesion (6-24 mo). Do not attempt surgical care for patients with myositis ossificans progressiva. Surgery is indicated when lesions mechanically interfere with joint movement or impinge on nerves.

References: eMedicine: Myositis Ossificans Mandar A Pattekar, MD, MS
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Additional Details:

Case Number: 1796932Last Updated: 12-07-2005
Anatomy: Skeletal System   Pathology: Non-Infectious Inflammatory Disease
Modality: CT, Conventional Radiograph, MRExam Date: 01-01-2000Access Level: Readable by all users

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