The increasing application of magnetic resonance (MR) imaging of the spine has raised the awareness of lumbar facet synovial cysts (LFSC). This well recognised, yet uncommon condition, presents with low back pain and radiculopathy due to the presence of an extradural mass. The commonest affected level is L4/5 with a mild degenerative spondylolisthesis a frequent associated finding. MR imaging is the technique of choice to detect and diagnose a LFSC. This pictorial essay, drawing on experience of 43 cases seen in 40 patients, illustrates the spectrum of appearances that can be encountered and suggest differing causes for the variable signal characteristics exhibited. Computed tomography (CT) can be of value in some cases to aid interpretation of the MR images. In addition, CT facet arthrography by injection of air or iodinated non-ionic contrast medium may be used to confirm the diagnosis in doubtful cases as well as noting whether the patients presenting symptoms can be provoked. A comprehensive review of the existing literature is presented.

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A variety of intrinsic and extrinsic tumours and tumour-like conditions may affect the infrapatellar (Hoffa's) fat pad (IFP). MR imaging is the technique of choice in evaluating these conditions, but correlation with radiographs is important to identify those lesions producing mineralization. This pictorial review illustrates the spectrum of mass-like lesions that can affect the IFP, emphasizing the radiographic and MR findings that suggest a specific diagnosis.

The aim of this study is to report the typical radiographic and MR imaging features of calcific myonecrosis, which help to distinguish this rare entity from other causes of a calcifying calf mass. Ten patients with a final diagnosis of calcific myonecrosis were referred to a specialist orthopaedic oncology service in a 5-year period with the presumptive diagnosis of malignancy based on recent clinical presentation and imaging findings. Radiographs were available for retrospective review in all ten cases and MR imaging in six. All patients presented with a slow-growing painless calf mass. All gave a history of major trauma to the lower leg many years before, but in only two cases did the referring clinician query whether trauma might be a contributory factor. Radiographs showed well-defined fusiform mineralised masses up to 25 cm in length arising within the calf. The calcification was consistently peripheral and plaque-like. Ossification was not present. MR imaging showed the anterior compartment to be involved in four cases and all compartments in two. T1- and T2-weighted images showed peripheral low signal intensity, more prominent on the T2-weighted images, because of the peripheral mineralization. The contents of the masses were variable on T1-weighted images depending on the differing amounts of blood breakdown products and were heterogeneous on T2-weighted images. The latter may be explained by a combination of the mineralisation and T2 shortening due to blood breakdown products. A gadolinium chelate, administered in two cases, failed to show any appreciable enhancement. Calcific myonecrosis has characteristic clinical, radiographic and MR features that should make the condition easy to recognise. Despite its rarity, it should be included in the differential diagnosis of focal mineralisation of the calf.

The aim of this study is to report the spectrum of imaging findings of intraosseous ganglia (IG) with particular emphasis on the radiographic and magnetic resonance (MR) features. Forty-five patients with a final diagnosis of IG were referred to a specialist orthopaedic oncology service with the presumptive diagnosis of either a primary or secondary bone tumour. The diagnosis was established by histology in 25 cases. In the remainder, the imaging features were considered characteristic and the lesion was stable on follow-up radiographic examination. Radiographs were available for retrospective review in all cases and MR imaging in 29. There was a minor male preponderance with a wide adult age range. Three quarters were found in relation to the weight-bearing long bones of the lower limb, particularly round the knee. On radiographs all were juxta-articular and osteolytic; 74% were eccentric in location, 80% had a sclerotic endosteal margin and 60% of cases showed a degree of trabeculation. Periosteal new bone formation and matrix mineralization were not present. Of the 29 cases that underwent MR imaging, 66% were multiloculated. On T1-weighted images the IG contents were isointense or mildly hypointense in 90% cases. Forty-one per cent of the cases showed a slightly hyperintense rim lining that enhanced with a gadolinium chelate. Thirty-eight per cent were associated with soft tissue extension and 17% with a defect of the adjacent articular cortex. Fifty-five per cent showed surrounding marrow oedema on T2-weighted or STIR images and two cases (7%) a fluid-fluid level prior to any surgical intervention. The authors contend that it is semantics to differentiate between an IG and a degenerate subchondral cyst as, while the initial pathogenesis may vary, the histological endpoint is identical, as are the imaging features apart from the degree of associated degenerative joint disease. IGs, particularly when large, may be mistaken for a bone tumour. Correlation of the typical radiographic and MR imaging features will indicate the correct diagnosis and obviate the need for biopsy.