Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

MUSCULOSKELETAL RADIOLOGY
Year
: 2012  |  Volume : 22  |  Issue : 1  |  Page : 35--39

Myositis ossificans imaging: keys to successful diagnosis


Alexis Lacout1, Mohamed Jarraya2, Pierre-Yves Marcy3, Juliette Thariat4, Robert Yves Carlier2,  
1 Centre d'imagerie Médicale, 47 Boulevard du Pont Rouge, 15000 AURILLAC, France
2 Department of Radiology, Hôpital Raymond Poincaré, Assistance Publique-Hôpitaux de Paris, Université Paris Ile-de-France Ouest, 104 boulevard Raymond Poincaré, 92380 Garches, France
3 Department of Head and Neck and Interventional Radiology, Antoine Lacassagne Cancer Research Institute, 33, Avenue Valombrose, 06189 Nice cedex1, France
4 Department of Radiation Oncology, Antoine Lacassagne Cancer Research Institute, 33, Avenue Valombrose, 06189 Nice cedex1, France

Correspondence Address:
Alexis Lacout
Centre d«SQ»imagerie Médicale, 47 Boulevard du Pont Rouge, 15000 AURILLAC
France

Abstract

Myositis ossificans (MO) is an inflammatory pseudotumor of the muscle that may be mistaken clinically and even histologically for a malignant soft tissue tumor. The aim of this article is to report the imaging characteristics of MO, the emphasis being on the early diagnostic clues. USG can be used at an early stage to reveal the «SQ»zone phenomenon,«SQ» which is highly suggestive of MO. A short course of nonsteroidal anti-inflammatory drug therapy may be an efficient treatment for early MO.



How to cite this article:
Lacout A, Jarraya M, Marcy PY, Thariat J, Carlier RY. Myositis ossificans imaging: keys to successful diagnosis.Indian J Radiol Imaging 2012;22:35-39


How to cite this URL:
Lacout A, Jarraya M, Marcy PY, Thariat J, Carlier RY. Myositis ossificans imaging: keys to successful diagnosis. Indian J Radiol Imaging [serial online] 2012 [cited 2019 Dec 8 ];22:35-39
Available from: http://www.ijri.org/text.asp?2012/22/1/35/95402


Full Text

 Introduction



In this article, we examine the performance of various imaging methods for the early diagnosis of myositis ossificans (MO) and optimal patient management.

MO is a pseudo-inflammatory tumor that originates from skeletal muscle and corresponds to a heterotopic, metaplastic, nonmalignant bone tumor. [1],[2] The etiology and potential predisposing factors of MO remain unclear. MO might develop secondary to a muscular trauma. However, in most cases no causative factor can be identified. [3] MO has a rich cortege of clinical symptoms, [1],[4] but one common presentation is as a very inflammatory, rapidly-growing, and painful muscular mass. [1],[4] In a typical case the dramatic onset and the symptom intensity strongly suggest the diagnosis of MO.

Two weeks from onset, MO displays specific histological characteristics that allow a definitive diagnosis to be made, provided that the biopsy has been performed adequately. [5] Conversely, in its early phase MO can be mistaken for a malignant soft tissue sarcoma. [5] Ossifications are usually observed in MO but should be distinguished from soft tissue ossifications of other causes, e.g., periarticular ossifications (paraosteoarthropathies) that usually occur in a context of central neurologic pathologies. [2],[6]

 Pathology



As MO develops it passes through three characteristic phases, leading to the so-called 'zone phenomenon'. The ossifications in MO are peripheral and centripetal, while they are central and centrifugal in osteosarcomas [5] [Figure 1], [Figure 2] and [Figure 3].{Figure 1}{Figure 2}{Figure 3}

The acute phase lasts one week. Histologically, the proliferation is composed of mesenchymal cells secreting a myxoid matrix as well as fibroblasts exhibiting numerous mitoses, which gives it a pseudo-fibrosarcomatous appearance. [5] This is followed by the subacute phase, which continues for about 10 days. The fibroblasts differentiate into osteoblasts and secrete an osteoid matrix at the periphery of the initial myxoid zone, giving it a pseudo-osteosarcomatous appearance. [5] The late phase, also called the maturation phase, usually starts between the second and fifth weeks of the evolution of MO. Bone production can be observed at the periphery of the lesion. At this stage, biopsy will reveal the three characteristic zones of MO and thus allow the correct final diagnosis to be made. [5] Later on in the evolution of MO, a fatty metaplastic evolution can also appear at the lesion center. [5]

On one hand, premature biopsy done at the early stage of MO may lead to a wrong diagnosis of sarcoma and, on the other hand, there is a risk that if biopsy is delayed a true sarcoma may be missed and result in tumor dissemination. It is therefore critical to identify the zone phenomenon of MO as early as possible using imaging. Another important feature that helps differentiate between MO and osteosarcoma is the well-circumscribed appearance of the former on histopathology.

 Imaging



Standard radiographs do not disclose any anomaly in the early stages of MO. [7] Radiographs repeated later on in the evolution of the disease may show de novo pathognomonic ossification surrounding a clear central area [Figure 4]; typically, these ossifications are distant from adjacent bony structures. However, the ossifications are often missed on radiographs when these are performed 2 to 3 weeks after MO onset and sometimes even later. [7] {Figure 4}

CT scan examination is more sensitive than radiography for detecting ossification and may also show a central fatty metaplastic area [8] [Figure 5], [Figure 6] and [Figure 7]. MRI may show the so-called zone phenomenon before ossification appears. On MRI scans, an iso- or slight hyperintensity can be observed within the intramuscular mass on T1W and T2W images respectively [9] [Figure 4] and [Figure 6]. MRI can also depict an inflammatory edema extending beyond the MO [Figure 6]. On gadolinium-enhanced T1W images, a hyperintense rim is suggestive of the zone phenomenon and may correspond to active hypervascularized osteoid matrix [10] [Figure 4] and [Figure 8]. This annular enhancement is distinct from the heterogeneous enhancement seen in sarcomatous tumors. [10] Although rim enhancement is common in the acute phase of MO, diffuse enhancement may also be seen [11] [Figure 5]. Starting in the subacute phase of MO, the rim may be hypointense on all MRI sequences, indicating mineralization [9] [Figure 4]. Other important imaging characteristics of MO include the lack of invasion of adjacent tissues and the presence of viable muscle fibers within the lesion, which are often involved in case of tumor. [7] {Figure 5}{Figure 6}{Figure 7}{Figure 8}

USG may be the most sensitive imaging modality to early depict the zone phenomenon in MO, as it can demonstrate this characteristic finding even before de novo ossifications can be reported on other imaging modalities [12] [Figure 4], [Figure 5] and [Figure 6]. Thomas et al. have described three concentric zones, corresponding to the above-described characteristic MO zones. The first zone, the most peripheral, is hypoechoic and encircles the lesion; contiguous hyperemia can be observed on Doppler usG0 [Figure 8]. The second, thinner, zone is hyperechoic and corresponds to the ossifications. The third, central, zone is hypoechoic and corresponds to the central stromal fibroblastic component. [12]

 Diagnosis



The diagnosis of MO is usually based on the patient's history (of trauma), clinical symptoms and on imaging findings when the zone phenomenon can be depicted. The main differential diagnosis is extraskeletal osteosarcoma, which in fact has 'mirror' characteristics both on imaging and pathology [Figure 9] The ossification phenomenon becomes first visible at two weeks. At that time, nonsteroidal anti-inflammatory drug (NSAID) therapy could be initiated leading to further clinical improvement and concomitant decrease of the soft tissue swelling and the echoic abnormality, thus preventing further useless invasive biopsy. When USG and diagnosis are delayed and the ossification is still visible, NSIA therapy could be administered. The final diagnosis should eventually be considered as the ossification progressively vanishes. If this is not the case, histologic confirmation would be necessary and biopsy should be performed by using USG and include the full length of the target lesion (complete sampling of the lesion). [5] {Figure 9}

 Treatment



Treatment is difficult owing to the chronological multistep process of MO. MO may heal and disappear spontaneously [Figure 5]. Surgical resection is sometimes suggested if the MO remains persistent; however, invasive surgical resection of the calcified tumor-like mass may compromise local function and lead to local relapse. [7]

Paraosteoarthropathies and MO share similar features: in both cases, the clinical onset includes inflammatory signs and evolution of disease is characterized by heterotopic bone production within soft tissues. [13] It is well recognized in the literature that nonsteroidal anti-inflammatory drugs (NSAID) may stop the evolutionary process of paraosteoarthropathies. [13] As mentioned previously, we suggest that NSAID might be used early to stop the evolutionary process of MO [14] [Figure 8]. Indeed, since efficacious treatment must be started early, it is necessary to diagnose MO as early as possible.

 Conclusion



We have described herein the utility of MRI and USG for the diagnosis of MO. USG is probably the most sensitive modality and might enable a very early diagnosis provided the radiologist bears in mind the patient's history (trauma, clinical symptoms) and the historadiological correlations of the zonation process evolution. Early NSAID treatment may prevent the appearance of ossification in MO and thus help prevent unnecessary biopsy.

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