Magnetic resonance imaging of myositis ossificans: analysis of seven cases

Myositis ossificans typically presents as soft tissue swelling with progressive ossification on radiographs. Since magnetic resonance imaging (MRI) is commonly used to evaluate soft tissue masses, we analyzed eight MR examinations in seven patients with myositis ossificans to determine if typical patterns were present. One acute lesion had homogeneous intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Two subacute lesions had low signal intensity margins with slightly increased signal intensity centers on T1-weighted images and very high signal intensity on T2-weighted images. Five chronic lesions had two different patterns. All five were well-defined with low signal intensity borders. Three had signal intensity patterns characteristic of fat on T1-weighted and T2-weighted images. The other two lesions had intermediate signal intensity on T1-weighted images and slightly increased signal intensity on T2-weighted images.We conclude that typical MR appearances of myositis ossificans do exist. A low signal intensity rim is a common finding. However, these patterns are not unique to myositis ossificans and resemble those that have been reported in other lesions. It is important to be aware of the spectrum of MR findings of myositis ossificans when considering the differential diagnosis of a soft tissue mass.     

MR imaging of myositis ossificans: Variable patterns at different stages

Five patients with a palpable mass at presentation underwent magnetic resonance (MR) imaging. The final diagnosis was myositis ossificans (MO). MR imaging features, particularly after injection of gadopentetate dimeglumine, mimicked those of an inflammatory mass or neoplasm. The lesions were excised in three patients, and the Images were correlated with histologic findings. Three different appearances were noted on MR images, corresponding to the stages of maturation of MO. Two cases Involved early-stage lesions, and Tl-weighted MR images showed a mass with homogeneous intermediate signal intensity. Both lesions showed rim enhancement after contrast agent injection and high signal intensity on T2-weighted images. Pathologic specimens demonstrated stroma with masses of spindle cells in which osteoid production was interspersed. The enhanced rim of the lesion mimicked the expected MR appearance of an abscess or necrotic tumor. Areas of enhancement in adjacent muscle were also seen on postcontrast T1-weighted images. Intermediate-stage MO was present in one case; there was evidence of a thin rim of calcification on plain radiographs and fatty changes in the lesion on T1-weighted Images, corresponding with histologic findings. One case of a mature lesion showed a considerable degree of peripheral calcification both on MR images and at histology. MR imaging is nonspecific in the diagnosis of early-stage MO.     

局限性骨化性肌炎的X线、CT表现

目的：探讨局限性骨化性肌炎的X线平片和CT表现,提高影像诊断水平。方法：回顾性分析19例经病理或随访证实局限性骨化性肌炎患者的X线、CT表现,其中19例均行X线平片检查,13例行CT检查。结果：X线表现为软组织内条片状或分层状骨化影;CT表现：早期（急性水肿期）局部肌肉水肿,无明确骨化成分,受累骨可出现轻微骨膜增生,中期（增殖肿块期）表现为分层状＂蛋壳＂样骨化,病灶中心呈软组织密度,晚期（骨化修复期）病灶局限,边界清楚,周围肌肉水肿消失,影像学表现为离心性分布的骨化团块。结论：局限性骨化性肌炎早期影像学表现缺乏特征性,容易误诊,中晚期分层状＂蛋壳＂样骨化对本病诊断有重要价值。     

MR imaging of extraabdominal desmoids: differentiation from other neoplasms.

A retrospective review of MR images of 36 patients with histologically proved extraabdominal desmoids was done to define the MR characteristics of these tumors and to determine if MR could be used to differentiate desmoids from other benign and malignant soft-tissue neoplasms. The desmoids evaluated included eight primary and 30 recurrent lesions. Our study was conducted in parallel with another study in which the MR appearance of 95 benign and malignant soft-tissue masses was evaluated, and the MR images of these masses were compared with our findings. The four desmoids from that study are included in our data. The signal intensity of the tumor on T1- and T2-weighted images was graded relative to the intensities of muscle and fat. Homogeneity, margin, neurovascular and bone involvement, and fibrosis (low-signal regions within the tumor on both T1- and T2-weighted images) were evaluated. On MR imaging, the desmoids showed inhomogeneous signal (97%), poor margination (89%), neurovascular involvement (58%), and bone involvement (37%). Fibrosis was present in 88% of primary desmoids and 90% of recurrent ones, and intermediate signal (greater than that of muscle and less than that of fat) was present in 75% and 50% of these, respectively. Our results show that the MR features of desmoids have characteristics that are commonly found in malignant tumors (inhomogeneous signal, poor margination, and neurovascular involvement). MR features of desmoids that distinguish them from malignant neoplasms are the presence of fibrosis and intermediate signal in the regions of the tumor.     

Surface-coil MR of orbital pseudotumor

Fifteen patients with clinical presentations compatible with idiopathic inflammatory orbital pseudotumor were examined by CT and MR imaging to determine if MR could add specificity to the CT appearance of this entity. MR was performed on a 1.5 T system, using surface-coil and head-coil techniques. Idiopathic pseudotumor was confirmed in nine patients on the basis of response to steroid therapy in the absence of local cause or systemic illness. One other patient had biopsy-proven idiopathic pseudotumor. Five patients proved to have other orbital entities, including metastases, infectious myositis, hemorrhage, and orbital sarcoid. In all 10 patients with confirmed pseudotumor, CT and MR were abnormal. MR abnormalities in 10 of 10 patients with pseudotumor were hypointense to fat and isointense to muscle on T1-weighted images. On T2-weighted images the lesions of pseudotumor were isointense or only minimally hyperintense to fat in nine of 10 cases; in one case, the enlarged muscle was markedly hyperintense to fat. The MR signal intensity of pseudotumor was similar to that found in infectious myositis and sarcoid. These findings contrasted to the MR appearance of the other disease entities examined. Metastases appeared markedly hyperintense to fat on T2-weighted images, while hematoma was hyperintense to muscle and isointense to fat on T1-weighted images and markedly hyperintense to fat on T2-weighted images. In our preliminary series, surface-coil MR appears to add specificity to the CT appearance of orbital pseudotumor.     

Inverted papilloma: evaluation with MR imaging.

The authors examined the magnetic resonance (MR) appearance of inverted papillomas to determine if this histologically benign lesion could be distinguished from malignancies of the sinonasal cavity. MR images in 10 patients with histologically proved inverted papilloma were retrospectively reviewed. The signal intensity of inverted papillomas on short repetition time (TR) images was iso- to slightly hypertintense to muscle in all 10 patients. Inverted papillomas had intermediate signal intensity on the long TR/echo time (TE) images. The tumors were iso- or slightly hypointense to fat on long TR/short TE images. In the seven patients who received gadopentetate dimeglumine, all inverted papillomas showed solid inhomogeneous enhancement. A review of eight sinonasal malignancies showed no distinctive signal intensity or enhancement characteristics to help differentiate inverted papillomas from various malignant tumors. The authors conclude that there is no signature MR appearance for the benign inverted papilloma. The main utility of MR imaging is in defining the extent of the lesion.     

Spinal angiolipomas: MR features.

PURPOSETo determine the MR features of spinal angiolipomas and to compare these findings with their histologic appearance.METHODSThe MR examinations of three patients with surgically proved angiolipomas were reviewed for tumor location and extent, signal characteristics, and pattern of contrast enhancement, and were then compared with the histologic findings.RESULTSFour tumors were found in the three patients, all located in the posterior epidural compartment, averaging about 2.5 vertebral bodies in length. On noncontrast T1-weighted images, all lesions were inhomogeneous and hypointense relative to epidural fat. Inhomogeneous enhancement was seen in three lesions on postcontrast T1-weighted images obtained with fat-saturation techniques. Angiolipomas were least conspicuous on T2-weighted images. A high vascular content correlated with the presence of large hypointense regions on T1-weighted images.CONCLUSIONSpinal angiolipomas are typically hyperintense on noncontrast T-1-weighted images relative to other tumors. Angiolipomas that contain large hypointense foci on noncontrast T1-weighted images can be expected to have a high degree of vascularity.     

Lymphangiomas in children: MR imaging

Seventeen lymphangiomas in 15 patients were imaged with magnetic resonance (MR) to define the nature, extent, and anatomic relationships of these lesions. The MR and pathologic findings were then compared to determine the histologic basis for the signal-intensity characteristics of these lesions. The signal intensity of 13 lesions was similar to or slightly less than that of muscle on T1-weighted images and greater than that of fat on T2-weighted images. This appearance correlated with the presence of ectatic lymphatic channels containing clear fluid on histologic section. Four lymphangiomas had high signal intensity, approximately equal to that of fat, on T1-weighted images, reflecting the presence of clotted blood or small cystic spaces with a higher ratio of fat to fluid. Sixteen of 17 lesions had visible septations on MR images. The authors' experience suggests that most lymphangiomas have a characteristic appearance on MR images. The information obtained with MR imaging can help in providing a preoperative diagnosis, in planning surgical resection, and in defining recurrence.     

MR and CT appearance of nodular fasciitis

Nodular fasciitis is a common soft-tissue tumor that remains almost unreported in the radiology literature. We retrospectively reviewed all available imaging studies on three patients with nodular fasciitis studied by MR at our institution. The lesions were round to oval in configuration, ranging in size from 1 to 4.5 cm. Two were intramuscular and one was subcutaneous in location. Both intramuscular lesions were poorly defined on CT, with a tissue attenuation less than that of skeletal muscle. The single subcutaneous lesion was well defined by surrounding fat. Conversely, all lesions were well defined on MR, although the appearance was otherwise nonspecific and varied according to the histology of the lesion. Both intramuscular lesions were mucoid or cellular and were hyperintense to skeletal muscle on T1-weighted and hyper-intense to fat on T2-weighted spin-echo (SE) MR images. The subcutaneous lesion was fibrous and markedly hypointense to skeletal muscle on all SE pulse sequences. Findings on three-phase bone scan, arteriography, and ultrasound are discussed. Because there are no unique radiologic findings in nodular fasciitis, this entity must be included in the preoperative differential diagnosis of small soft-tissue masses occurring in the extremities of young adults.     

Nodular fasciitis: correlation of MRI findings and histopathology

OBJECTIVE: To compare the histopathology of nodular fasciitis (NF) with the magnetic resonance imaging (MRI) findings in order to evaluate the basis of the MR signal characteristics. DESIGN AND PATIENTS: Ten patients with NF, nine females and 1 male, with an age ranging from 13 to 58 years (mean 26.8 years) were studied. MRI findings, available in all 10 patients, were compared with the histopathology in nine patients, and an area-to-area comparative study of the whole specimen section histopathology and MRI was performed in two patients. RESULTS: On the basis of an excisional biopsy or resection specimen, the nine lesions were classified into myxoid ( n=4), cellular ( n=3) and fibrous ( n=2) subtypes. Four myxoid lesions with a subcutaneous location showed a homogeneous SI comparable with muscle on T1-weighted images, high SI on T2-weighted images, and had homogeneous enhancement. One cellular lesion presented with homogeneous, slightly higher SI than muscle on T1-weighted images and inhomogeneous, high SI on T2-weighted images. Alcian blue stain of the whole specimen section revealed the lesion had two parts corresponding to different enhancement patterns on MRI. The blue-stained myxoid part showed markedly diffuse enhancement, while the non-stained cystic space had only peripheral enhancement. Two other cellular lesions had the same appearance on both T1- and T2-weighted images and showed inhomogeneous, diffuse enhancement. One fibrous subtype lesion presented with inhomogeneous, overall slightly higher SI than muscle on T1-weighted images, lower SI at the periphery and high SI in the center on STIR images and only peripheral enhancement. Microscopy and CD-31 staining of the lesion showed more extracellular matrix, with poor vascularity in the center and more collagenous matrix with higher vascularity at the periphery. CONCLUSION: Although similar findings were found in some lesions, the large histologic variability of NF hampers the definition of a prototype of NF on MRI. However, the MRI appearance of the myxoid subtype is rather characteristic. Histologic findings reflect the different SI characteristics and enhancement pattern on MRI.     

Foci of decreased signal on T2-weighted MR images in leiomyosarcomas of soft tissue: correlation between MR and histological findings

OBJECTIVE: Leiomyosarcomas are rare soft tissue sarcomas with varying MR signal characteristics and histologic pictures. The purpose of this study was to investigate the histological features of foci, which showed decreased signal on T2-weighted images in leiomyosarcomas of soft tissue. MATERIAL AND METHODS: We reviewed the MR images of six histologically proved cases of leiomyosarcomas of soft tissue and correlated the foci, which showed decreased signal on T2-weighted images with the histologic findings. RESULT: Microscopic examination revealed that these foci were composed of hyalinization of neoplastic tissue, internal septations, deposition of hemosiderin, or corresponded to metaplastic bone. CONCLUSION: The authors explain that the foci of decreased signal on T2-weighted MR images correspond to tissue components of the lesion, particularly fibrous tissue, hemosiderin and metaplastic bone. So, the suggestion is that leiomyosarcoma should be considered in the differential diagnosis of soft-tissue tumors that show foci of decreased signal on T2-weighted MR images.     

Periosteal chondroma: MR characteristics

PURPOSE: The purpose of this study was to describe the MR characteristics of periosteal chondroma. METHOD: MR images of 12 proven cases of periosteal chondroma were analyzed with reference to tumor morphology and size. MR features were correlated with radiographic and pathologic findings. RESULTS: Tumor size ranged from 1 to 7 cm in maximum diameter with a mean value of 2.6 cm. On MR images, a soft tissue mass at the bone surface with pressure erosion of adjacent cortical bone could be identified in all cases. All lesions were bordered by a hypointense rim (100%) and frequently showed a lobulated configuration (75%). Edema of medullary bone or soft tissues was not observed in any of the cases. Signal intensity of cartilaginous tumor tissue was typically hypo-or isointense relative to muscle on T1-weighted (100%) and hyperintense relative to fat on T2-weighted (92%) and T2*-weighted (100%) MR images. Radiographically significant calcifications of the tumor matrix, present in half of the cases, caused focal signal loss on MR images of all pulse sequences. Contrast enhancement was observed predominantly at the periphery of the lesions (100%), which on pathologic examinations typically contained fibrovascular bundles, surrounding the cartilage lobules. CONCLUSION: Periosteal chondroma appears to have a relatively typical MR appearance, which reflects the histologic composition of the lesion. In addition to radiography, MRI therefore can substantially aid in the preoperative diagnosis of this rare bone lesion.     

Sialoblastoma (embryoma): MR findings of a rare pediatric salivary gland tumor.

We report the findings in a 21-month-old girl who had a noninfiltrating mass in the left cheek, just anterior to the masseter muscle, which, at surgery, proved to be a sialoblastoma. Sialoblastoma has a histologic appearance reminiscent of a primitive state of salivary gland development; that is, it shows an arrested state of salivary maturation. MR imaging in this case showed that the lesion was isointense with muscle on T1-weighted images, had a high-intermediate signal intensity similar to that of fat on T2-weighted images, and enhanced sparsely and nonhomogeneously.     

Cross-sectional imaging of primary osseous hemangiopericytoma

The aim of this study was to assess cross-sectional imaging features and the value of CT and MRI in primary hemangiopericytoma of bone. In five patients with histologically proven primary osseous hemangiopericytoma CT and MR scans were evaluated retrospectively. Both CT and MRI were available in four patients each. In three patients both imaging techniques were available. On CT primary hemangiopericytoma of bone presents as an expansive lytic lesion with bone destruction and inhomogeneous contrast enhancement. Magnetic resonance imaging depicts osseous hemangiopericytoma as hyperintense lesion on T2-weighted images with intermediate signal intensity on T1-weighted images. Curvilinear tubular structures of signal void in the tumor matrix on T1-weighted images and corresponding hyperintense structures on T2-weighted and on fat-suppressed short tau inversion recovery images were present in three patients. Although cross-sectional imaging findings are non-specific, they add to the diagnosis and provide valuable information about the extent of bone destruction and local tumor spread in patients with primary osseous hemangiopericytoma. While CT demonstrates the extent of bone destruction best, MRI better visualizes medullary and soft tissue extension of the tumor. Curvilinear signal abnormalities support the diagnosis of hemangiopericytoma of bone. This imaging pattern is best visualized on fat-suppressed or contrast enhanced T1-weighted MR images.     

Chemical-shift MR imaging of the femoral head: an in vitro study of normal hips and hips with avascular necrosis

To study the conventional and chemical-shift MR images of fatty, hemopoietic, and ischemic bone marrow, four normal femurs from autopsies and six femoral heads from total hip replacement done for avascular necrosis (AVN) were imaged with a small-bore 1.4-T MR unit. T1- and T2-weighted spin-echo images, fat- and water-selective spin-echo images, and out-of-phase images were obtained. The specimens were then sectioned, radiographed, and studied histologically. The capital epiphysis and greater trochanter in normal femurs had the highest signal on T1-weighted, fat-selective, and out-of-phase images owing to their high fat content. Fat-selective and water-selective images accurately depicted regions of fat and water, whereas T1-weighted, T2-weighted, and out-of-phase images were misleading in some cases. On T2-weighted images, a double line consisting of a rim of low signal with a high-signal inner border was noted surrounding AVN lesions. Histologic correlation showed that the low-signal outer rim was due to sclerotic bone, while the high-intensity inner border was due to granulation tissue and/or chondroid metaplasia. Fractures within the six AVN lesions were best seen on T2-weighted images, but these could not be distinguished from granulation tissue. On T2-weighted images, the weight-bearing cartilage had lower signal in five of six femoral heads with AVN. We conclude that the MR appearance of AVN reflects its complex histopathology. Direct spin-echo chemical-shift imaging can help correlate MR images with histology by providing information not available from conventional or out-of-phase images.     

Giant cell tumor of the proximal tibia: MR and CT appearance

The magnetic resonance (MR) appearance of four cases of giant cell tumor (GCT) of the proximal tibia are described and the MR grading of these tumors is compared with CT and conventional radiography. Magnetic resonance showed the lesions to be well defined with respect to adjacent marrow and cortical bone. Homogeneous intermediate signal intensity or low signal within the tumors was seen on T1-weighted images. T2-weighted images showed mixed signal intensity with small "bright patches" of increased signal intensity in all four cases. No fluid levels were identified. Magnetic resonance was superior to CT and plain radiography in radiologic grading of the tumors. Computed tomography was superior in determining if cortical invasion was present. Intraarticular tumor extension was more accurately detected by MR and arthrotomography than CT. An MR manifestation of GCT of the proximal tibia is described which may be a common appearance of this tumor by this modality. Magnetic resonance is the procedure of choice in the radiologic grading of GCT.     

Hepatocellular carcinoma: correlation of MR imaging and histopathologic findings.

Seventy-two histologically proved nodular hepatocellular carcinomas (HCCs) were studied with magnetic resonance (MR) imaging at 1.5 T. Capsules were present in 56 of the 72 tumors. Thirty-seven capsules were depicted on T1-weighted spin-echo MR images, and 16 were depicted on T2-weighted MR images. Visualization was dependent on thickness and structure of the capsules. Of the 72 tumors, 36 had a mosaic pattern. A mosaic pattern was visualized in 12 of the 36 tumors on T1-weighted images and in 27 of the 36 tumors on T2-weighted images. Six tumors were determined to be histologic grade 1, and all were hyperintense on T1-weighted images, regardless of whether intracellular fat deposits were present. Four of the six grade 1 tumors were isointense on T2-weighted images. In contrast, grades 2 and 3 tumors had various signal intensities on T1-weighted images and most were hyperintense on T2-weighted images. Twenty-one of 32 tumors (66%) with focal areas of increased signal intensity on T2-weighted images had intratumoral dilated sinusoids at histologic examination.     

MRI of ganglioneuroma: histologic correlation study

PURPOSE: The purpose of this study was to evaluate the MR findings of ganglioneuroma and to correlate imaging and histologic features. METHOD: Conventional SE and contrast-enhanced dynamic MRI was used to examine 10 patients with pathologically confirmed ganglioneuroma. The morphologic features, signal intensity, and dynamic enhancement pattern of the tumors were retrospectively analyzed and correlated with histologic features. RESULTS: Capsules were present in all tumors histologically and were also detected in five tumors on postcontrast T1-weighted images. A whorled appearance corresponding to interlacing bundles of Schwann cells and collagen fibers on histologic specimens was visualized in five tumors on T1-and/or T2-weighted images. Tumors with markedly high signal intensity on T2-weighted images consisted histologically of a large amount of myxoid stroma and relatively few cellular and fibrous components. Tumors with intermediate to high signal intensity consisted of numerous cellular and fibrous components and little myxoid stroma. Early enhancement of tumors was usually lacking in dynamic MR studies; however enhancement gradually increased. CONCLUSION: The results suggest that the MR features of ganglioneuroma are well correlated with histologic findings.     

MR features of tuberculous osteomyelitis

OBJECTIVE: To describe the MR imaging features of tuberculous osteomyelitis. DESIGN AND PATIENTS: MR imaging features of 11 patients (14-65 years) with proven extra-spinal tuberculous osteomyelitis were reviewed. Osseous and adjacent soft-tissue changes were analyzed. RESULTS: On the basis of the signal intensity characteristics compared with the normal marrow fat, two kinds of lesions were observed: (a) predominantly intermediate to low signal intensity lesions on T2-weighted images with low signal intensity on T1-weighted images, and (b) lesions which had a discrete peripheral zone of marginally higher signal intensity than the center on T1-weighted images and surrounding edema and lower signal intensity than the fatty bone marrow with variable signal intensity on T2-weighted images. Soft-tissue abscesses and marrow edema were each noted in eight cases. Soft-tissue edema was noted in most cases. CONCLUSION: An osseous lesion with intermediate to low signal intensity on T2-weighted images and associated soft-tissue abscess may be suggestive of tuberculous osteomyelitis. Lesions with a rim of mildly increased signal intensity on T1-weighted images, a non-specific indicator of an infective process, may also be seen.     

MR imaging findings in patients with bone-chip allografts

Increasing use of MR to evaluate primary bone neoplasms has stimulated numerous articles on the initial assessment of these lesions. However, scant MR literature has been written about the postoperative MR appearance. We studied the MR appearance of lesions treated by curettage followed by packing with cancellous bone-chip allograft. We retrospectively reviewed the MR scans of 18 consecutive patients treated in this way. Pathologic diagnoses of these lesions were confirmed according to commonly accepted criteria. The allograft sites showed a distinctive pattern of speckled bright signal on T1-weighted images in eight cases. Thirteen of 18 grafts showed a whorled or speckled pattern of increased signal on the T2-weighted images. Only four allograft regions had predominantly low signal on both T1- and T2-weighted images. Two of 18 patients had recurrent tumor proved by open biopsy. MR images in these cases showed areas of homogeneous signal that replaced areas of speckled hyperintensity on both T1- and T2-weighted images. In both these recurrences the tumor had signal intensity similar to that seen on the preoperative MR study. We conclude that knowledge of the MR appearance of cancellous bone chip allografts is important to avoid misinterpreting areas of high signal on T1- or T2-weighted images as areas of recurrence of tumor and/or hemorrhage.