How to Read an MRI for Avascular Necrosis

Avascular necrosis is bone death at a cellular level. Avascular necrosis results from lack of blood supply to the bone, depriving cells of nutrients. Avascular necrosis is also known as osteonecrosis. The most common area for avascular necrosis is the hip. Avascular necrosis results from damage to joints, low blood supply or increased pressure within the bone. Necrosis of the bone is an irreversible process, therefore medical intervention is necessary once necrosis begins in order to prevent further damage to the body.

Instructions

MRI & Diagnosis

• 1

  Magnetic resonance imaging or MRI is the most sensitive test for detecting avascular necrosis in the bone. MRI is able to detect the size of the lesion as well as the stage of the lesion. This allows therapy to be initiated in order to prevent further damage to the bone. MRI does not use ionizing radiation, which is important regarding growing bones. MRI images are done through various angles, ensuring all views for better diagnosis, including saggital, axial and coronal views.

• 2

  In bone two types of marrow are visually seen on MRI. Fatty marrow is shown as a high signal intensity while hematopoeitic marrow is shown as a low signal intensity on MRI scans. The medullary cavity of the bone on MRI are oriented vertically and show striations of low signals on MRI. Surrounding the medullary cavity is a cortex of the bone represented by a sharp demarcated line. In avascular necrosis the cortex will show low signal intensity on an MRI due to low concentration of hydrogen ions normally carried in blood.

• 3

  Avascular necrosis begins in a small area, and patients are usually asymptomatic. If the lesion does not heal, the necrosis progresses to the articular cartilage. Ineffective resorption of dead bone will result in more damage to the bone. On radiography the dead bone has a cystic and sclerotic appearance.