DIAGNOSIS AVASCULAR NECROSIS OF THE FEMORAL HEAD USING MR IMAGING NUCLEAR MEDICINE AND MEDICAL RADIOLOGY DEPARTMENT

Аннотация

Due to the pattern of its blood supply, the femoral head is particularly vulnerable to avascular necrosis (AVN). Nontraumatic AVN is a devastating disorder affecting young patients, and despite treatment it normally follows a progressive course toward a destructive osteoarthropathy. Magnetic resonance (MR) imaging is currently used in major classification systems solely for early detection of femoral head AVN when plain radiographs are normal. More recent data have shown that MR imaging may improve staging, investigate radiologically occult collapse, depict other causes of disability and pain, assess prognosis, and evaluate treatment. This article reviews the established and evolving knowledge on MR imaging strategies and their role to visualize areas and staging lesions of the hip joint with AVN of the femoral head. Keywords: hip, osteonecrosis, avascular necrosis, radiation diagnostics. Introduction: The main clinical manifestations in the pathology of hip joints are pain in the joint, in groin region with irradiation along the femoral nerve to the knee joint and the gluteal region during physical exertion, sometimes night pains also bother. Often, the pathology of the hip joint manifests itself in the form of indistinct reflected pain in the knee joint. The smoothness of the contours of the hip joint and soreness during palpation are objectively determined. Restriction of rotational movements in the joint, abduction,reduction and flexion are also limited, painful. Magnetic resonance (MR) imaging is highly sensitive in depicting early AVN and is considered the method of choice for accurate diagnosis and is staging of the 117 https://biti.uz/konferensiya/konferensiya2025/index.html 21 апреля 2025 г. disease. MR imaging can also assess severity and prognosis, depict the presence of multiple foci of involvement, and guide and follow up the surgical treatment. MR imaging is also used for the detection of minimal AVN lesions. This article reviews the established and evolving knowledge on MR imaging strategies and their role to visualize areas and staging lesions of the hip joint with AVN of the femoral head. Materials and methods: The presence of a circumscribed subchondral "bandlike" lesion with low signal intensity (SI) on Tl-weighted sequences is considered pathognomonic of AVN. We can see "double-line" sign on non-fat- suppressed T2-weighted SE and TSE images which is virtually diagnostic of AVN. It occurs at the interface between viable and nonviable tissue and consists of an outer low SI rim (suggested to represent reactive sclerotic bone) and an inner high SI rim (considered to represent vascular granulation tissue and/or chondroid metaplasia). Mitchell et al was first who described and found this sign in 85% of AVN lesions. According to the SI of the region within the double line and based on the chronological order of its appearance, Mitchell et al proposed a classification system ranging from A (early stage, retaining normal fat SI) to D (advanced stage, low SI due to fibrous tissue and sclerosis). This system has not been used widely because it does not correlate with radiographic staging and prognosis[10]. Besides its definite association with histopathological changes, the "double- line" sign is considered to reflect a chemical shift artifact notified at the frequency encoding direction axis of the field. Although the double-line sign has the characteristics of an artifact, this does not alter its diagnostic significance. Nowadays, there is widespread use of T2-weighted TSE sequences with spectral fat saturation (to overcome the JJ-coupling effect that leads to bright fat) and thus, the double-line sign is not seen but rather manifests as a "bright band-like" sign evident also on contrast-enhanced Tl-weighted sequences. Subchondral fractures in AVN typically occur as low SI lines on Tl-weighted MR images and can be 118 https://biti.uz/konferensiya/konferensiya2025/index.html 21 апреля 2025 г. differentiated from subchondral insufficiency fractures in osteoporotic women based on the shape of the lesion: In AVN, the low SI band is smooth, concave to articular surface, and circumscribes all of the necrotic segment, whereas in insufficiency fractures the low SI band is irregular, discontinuous, and convex to the articular surface. On T2-weighted SE MR images, subchondral fractures may have a variable SI because the fracture may be filled by gas or fluid. MR imaging has been found to be less sensitive than computed tomography (CT) in detecting subchondral fractures in AVN: Extension of the fracture line through the cortex in CT is seen in 70% of patients who do not show any evidence of fracture with MR. In our experience (unpublished data), modern MR scanners in the appropriate protocol setting including unilateral two-dimensional and/or three-dimensional high-resolution images, are able to demonstrate the subchondral fracture equally or even better than CT, the latter being limited from the radiation