Magnetic resonance imaging of the musculoskeletal system. Part 9. Primary Tumors

Diagnostic imaging of the canine stifle: a review

The stifle joint, a common location for lameness in dogs, is a complex arrangement of osseous, articular, fibrocartilaginous, and ligamentous structures. The small size of its component structures, restricted joint space, and its intricate composition make successful diagnostic imaging a challenge. Different tissue types and their superimposition limit successful diagnostic imaging with a single modality. Most modalities exploit the complexity of tissue types found in the canine stifle joint. Improved understanding of the principles of each imaging modality and the properties of the tissues being examined will enhance successful diagnostic imaging.

Parameters for Diffusion Weighted Magnetic Resonance Imaging for Temporomandibular Joint

The purpose of this study was to determine optimum diffusion parameters for diffusion weighted imaging (DWI) techniques, including echo planer imaging (EPI), single-shot fast spin echo (SSFSE), and steady-state free precession (SSFP) in Magnetic Resonance Imaging (MRI) of the Temporomandibular Joint (TMJ). A polyethylene tube with distilled water was individually positioned at the external acoustic meatus foramen in each of three volunteers with normal healthy TMJs. Images were obtained using three types of DWI at differing diffusion parameters, b-factors, and diffusion moment. Signal intensity and imaging ability for various anatomical structures, including the distilled water, were evaluated from each image. The details of the anatomical structures of the TMJ were unidentifiable in the images produced with EPI and SSFSE, but were identifiable on the SSFP images. A diffusion moment value from 100 mT/m(*)msec to 150 mT/m(*)msec for SSFP, in particular, restrained the signal intensity of the water, thereby protecting the comparably high image quality of the TMJ structure. In conclusion, only SSFP is capable of allowing interpretation of emerging pathologic conditions in the TMJ region, when used with a diffusion moment set at between from approximately 100 mT/m(*)msec to 150 mT/m(*)msec.

Epidiaphyseal versus other intercalary allografts for tumors of the lower limb

Epidiaphyseal intercalary reconstruction has become possible for bone tumors that extend into the epiphysis because advances in magnetic resonance imaging and chemotherapy allow close resection while sparing the juxtaarticular bone and joint. In a retrospective study, we questioned whether epidiaphyseal reconstructions around the knee had a clinical outcome (measured as long-term survival, complication rate, and functional score) comparable with metadiaphyseal and diaphyseal reconstructions. Between 1988 and 1999, 14 epidiaphyseal, nine metaphyseal, and 12 diaphyseal reconstructions were done, and the median followup was 7.2 years. Kaplan-Meier analysis showed a 10-year survival rate of 79% for epidiaphyseal reconstructions, which did not differ from an 89% rate for metadiaphyseal and a 75% rate for diaphyseal reconstructions. Epidiaphyseal complications included two infections, five fractures, and three nonunion treatments. Complications for all 35 grafts included three infections, 12 fractures, and nine nonunion treatments. Ultimately, six grafts failed, with infection and length of resection as predisposing factors. All epiphyseal osteotomies had tumor-free margins and no local recurrences. The mean Musculoskeletal Tumor Society score for each type of intercalary reconstruction was between 23 and 24. Because the epidiaphyseal reconstruction avoids complications associated with joint reconstruction and the results are comparable with those of other types of intercalary grafts, these reconstructions should be considered if at least 1 cm of tumor-free juxtaarticular bone can be maintained.

Can FDG PET be used to successfully direct preoperative biopsy of soft tissue tumours?

Magnetic resonance imaging (MRI) has been the most useful tool in the anatomical definition of soft tissue sarcoma, although there remains the problem of defining the lesions as benign or malignant. The management of such lesions requires biopsy prior to surgical resection. If the most malignant area could be defined more accurately, then this area could be targeted for biopsy. Fluorodeoxyglucose positron emission tomography (FDG PET) has been found to be useful in identifying malignancy and variations in grade in soft tissue masses. The aim of this study was to assess the use of FDG PET scanning with or without co-registered MRI to indicate the most appropriate biopsy site. Twenty consecutive patients presented with soft tissue masses with clinical signs of malignancy. All patients underwent MRI and FDG PET scanning and the two images were co-registered. A biopsy site that was the most likely to be malignant was defined on the PET scan. All patients underwent an initial biopsy and then complete surgical resection of the mass. The histological results from the mass were compared with those from the biopsy specimen obtained from the site suggested by the PET scan. In malignant masses the biopsy site suggested by the FDG PET scan was found to be representative of the most malignant site on the whole mass histology. Benign lesions had low or no FDG uptake. In no case did the co-registered image add significantly to the appropriate biopsy site. FDG PET can be used to appropriately direct biopsy in soft tissue sarcoma and potentially may lead to computed tomography/MRI directed outpatient biopsy prior to definitive treatment.

Comparison of radiography, computed tomography, and magnetic resonance imaging for evaluation of appendicular osteosarcoma in dogs

OBJECTIVE

To determine which imaging modality best determines the microscopic extent of primary appendicular osteosarcoma in amputated limbs in dogs.

DESIGN

Case series.

ANIMALS

10 dogs with appendicular osteosarcoma.

PROCEDURE

10 dogs with appendicular osteosarcoma that did not receive neoadjuvent chemotherapy were treated by use of limb amputation. Amputated limbs were imaged by use of radiography, computed tomography (CT), and magnetic resonance imaging (MRI) and examined microscopically to determine longitudinal extent of neoplastic cell involvement and length of associated intramedullary fibrosis. Changes detected by use of the various imaging studies were compared with the actual tumor length determined microscopically. Data were analyzed to determine which imaging technique most closely predicted tumor length.

RESULTS

Measurements obtained by use of craniocaudal radiographic views were most accurate at predicting tumor length but underestimated tumor length substantially in 1 limb and slightly in another limb. Measurements made by use of CT were most accurate at predicting tumor length when intramedullary fibrosis was taken into account but underestimated tumor length in 1 limb. Measurements made by use of MRI were least accurate but did not underestimate tumor length in any of the limbs.

CONCLUSIONS AND CLINICAL RELEVANCE

Although radiography is used in diagnosis of osteosarcoma in dogs, additional imaging studies to confirm the extent of neoplasia prior to limb-sparing ostectomy may be beneficial. Underestimation of tumor length would be associated with higher incidence of incomplete excision and local tumor recurrence.

The role of imaging modalities in the diagnosis of primary dedifferentiated parosteal osteosarcoma

Dedifferentiated parosteal osteosarcoma (dd-POS) is defined as high-grade sarcomatous components coexisting with low-grade POS components. With regard to the histological diagnosis of dd-POS, the sampling of a small area of dedifferentiation through the densely mineralized POS can be a problem. In this situation, imaging is important to identify the area with the highest possibility of dedifferentiation. We report a patient in whom dedifferentiation was shown by computed tomography (CT) and magnetic resonance imaging (MRI). CT revealed a radiolucency in a highly mineralized area. T2-Weighted MRI showed a relatively high signal intensity, corresponding to the radiolucency, surrounded by a very low signal intensity area. Furthermore, gadolinium-enhanced T1-weighted MRI showed marked enhancement. Based on these imaging techniques, the condition was diagnosed as most likely to be a dd-POS, although a representative sample was not accessible by incisional biopsy. Neoadjuvant chemotherapy was administered, followed by wide resection and adjuvant chemotherapy. Four years after the surgery, partial lobulectomy was required because of a pulmonary metastasis. Three years after the second surgery, the patient remained well without evidence of metastases. Based on the initial diagnosis and, consequently, the optimal treatment of combined chemotherapy and wide resection, our patient showed a good clinical outcome.

Clinical and radiographic evaluation of bone tumors

Timely diagnosis of osseous tumors is essential in providing proper management. Appropriate imaging studies are essential to this process, however, if inconclusive, they can be superceded by information obtained through the patient history and physical examination.

Ewing's sarcoma of the mandible: radiologic features with emphasis on magnetic resonance appearance

Ewing's sarcoma is an uncommon malignancy that usually occurs in children. A case of Ewing's sarcoma of the mandible is presented, and the radiologic appearance is described, with special consideration given to the magnetic resonance imaging features.

Magnetic resonance imaging features of multilobular osteochondrosarcoma in 3 dogs

Three dogs with multilobular osteochondrosarcoma of the skull were evaluated using magnetic resonance (MR) imaging. Spin echo T1, T2, proton weighted and post contrast T1W images were obtained with a 1.5 Tesla magnet. The MR imaging findings were similar in all three dogs with mixed signal intensities in the T1W, T2W and proton weighted images and fairly large areas of contrast enhancement in the post contrast T1W images. The extent of brain and soft tissue involvement were well delineated and provided useful information concerning surgical planning. MR imaging provided a useful method of evaluating dogs with skull tumors.

Bone and soft tissue tumors: the role of contrast agents for MR imaging

Magnetic resonance imaging is an important modality for the imaging evaluation of musculoskeletal tumors. Although there is general agreement on the value of unenhanced MR in detection, diagnosis and staging, intravenous use of gadolinium-contrast media (gd-CM) is indicated in selected cases. The purpose of this article is to review the basic pharmacokinetic principles and imaging techniques for static and dynamic contrast-enhanced MR imaging and to highlight the most important indications for administration of gd-CM in patients with musculsokeletal tumors and tumor-like lesions: adding specificity in tissue characterization, staging of local extent and biopsy planning, monitoring preoperative chemotherapy and detection of recurrence.