A Survival Guide to Musculoskeletal Imaging

The current diagnostic concept is to embed imaging in the assessment systems in rheumatology. This means that imaging should contribute to the detection of early arthritis and to the quantification of abnormalities with prognostic impact. With the combinations of joint pain, laboratory indicators of inflammation and imaging features of tendovaginitis, joint effusion and/or bone marrow inflammation subforms of early arthritis may be defined. Synovitis is today regarded as part of a systemic autoimmunologic disease, and certain phenotypes can be classified with relation to the fibroblastic response and different interleukin expression leading to a destructive-erosive, a sclerotic-proliferative or a mixed imaging appearance. With US and radiography, followed by MRI, the patterns of arthritis and their differentiation from normal anatomic structures can be assessed and displayed in dedicated structured reporting templates. The differential diagnosis of autoimmune-mediated arthritis includes crystal-induced arthropathies, erosive osteoarthritis, posttraumatic and other forms of secondary joint inflammation.

A systematic approach to analysing trauma imaging of the peripheral skeleton is presented. Typically, imaging begins with x-rays. A step-wise approach may reveal subtle abnormalities that should prompt further action. For example, the presence of a Second fracture on x-ray suggests an ACL injury and thus should lead to an MRI scan. It should be recognised that in trauma, certain injuries cannot occur in isolation; therefore a dislocated radial head on elbow x-ray should prompt imaging of the whole forearm, as Monteggia fracture-dislocation may be present. Understanding mechanisms of injury allow the radiologist to predict patterns of injury. So if bone bruising is present on MRI in the lateral femoral condyle and medial patella, a lateral patellar dislocation should be suspected, and a specific search for an injury of the medial retinaculum should be made. Conversely, recognising classic patterns of injury can allow the mechanism of injury to be deduced. This lecture will focus on classical patterns of acute trauma in the peripheral skeleton.

In this lecture, we’ll focus on imaging osteomyelitis of the appendicular and axial skeleton, and their differential diagnosis using radiographs, US, and especially MRI and PET-CT. Understanding the interaction between invading organisms and intact or compromised host response is essential in the interpretation of imaging features. Major routes of infection include hematogeneous or contiguous routes occurring in respectively pediatric-geriatric, or immunocompromised and diabetic, or post-procedure infections. Location in the metaphysis and vertebral body are hallmarks of hematogenous spread. Location in bones close to skin defects, pressure points, and soft tissue infection are hallmarks of contiguous spread, especially in diabetic foot, intensive care patients, and following surgical or image guided procedures. Knowledge of age and the comorbidity-related relationship between vasculature on one-hand and growth plates and discs, on the other hand, is essential in the diagnosis of infection. Also, imaging features of host response depend on the pressure within anatomical compartments. The most relevant differential diagnostic issues including posttraumatic sequelae, degenerative disease, Charcot foot and spine, sterile inflammatory disease (CRMO, SAPHO), tumours, and also the differentiation between mild and life-threatening infection like necrotising fasciitis will be discussed. The impact of imaging on clinical outcome as it depends on treatment options, cost-effectiveness, predictive values of various imaging studies relative to clinical and laboratory tests, is addressed.

The diagnosis of a bone tumour is based on clinical findings, the age of the patient, the anatomic location of the lesion, its radiologic appearance, and if imaging does not allow for a specific diagnosis, its histopathologic features. Radiography remains the initial imaging modality for evaluation of the location of the lesion with respect to the longitudinal and axial planes of the involved bone, for estimation of its biologic activity by analysing the patterns of bone destruction and periosteal response, and for the depiction of matrix mineralisation. CT is typically used to obtain “radiographic” information in regions of complex skeletal anatomy such as the skull, spine, pelvis and shoulder girdle. MR imaging is best suited to determine the local extent of a bone tumour (local staging), but can also be helpful to narrow the differential diagnosis in specific lesions such as cysts and cartilage-forming tumours. With a clear emphasis on conventional radiography, this course will review the basic imaging features of the most common benign and malignant bone tumours. Important radiographic findings, such as bone destruction patterns, types of periosteal reactions and matrix mineralisation, will be explained step by step in correlation with histopathology as well as advanced imaging techniques.