Avascular necrosis (Osteonecrosis)

  • Avascular necrosis (AVN) is death of a bony structure secondary to insufficient blood supply.
  • Primary pathology is of unknown aetiology, but secondary AVN is linked with a variety of pathologies.
  • Idiopathic avascular necrosis occurs in childhood in the proximal femoral epiphysis and it is known as Perthes’ disease.
  • Associated with steroid use, alcohol abuse, metabolic disease (e.g.Gaucher’s disease), vasculitis (SLE), sickle cell disease, malaria, occupational causes (e.g. deep-sea divers – caisson disease), venous thromboembolism and bone-marrow transplants.
  • Certain bones in adulthood are particularly associated with AVN; e.g. femoral head, distal femur, proximal humerus – idiopathic and post-traumatic, talus, lunate – Kienbock’s disease, metatarsal head – Freiburg’s disease for second metatarsal head, navicular – Kohler’s disease, scaphoid – Preiser’s disease and capitellum – Panner’s disease – associated with osteochondritis.
  • Clinically present with pain of insidious onset and the pain often worse at night. Pain is usually severe and often becomes more bearable after several weeks. Joint locking with loose bodies – separated osteochondral fragments. Reduced function of adjacent joints.
  • The initial radiograph if taken early may be normal. The affected bone becomes sclerotic with later collapse and remodelling. Degenerative changes within adjacent joints. MRI is 90–100% sensitivity for symptomatic disease.
Freiberg’s osteonecrosis of the second metatarsal head
Freiberg’s osteonecrosis of the second metatarsal head.

The groin and the inguinal region

In both men and women, the groin (inguinal region) is a weak area in the abdominal wall.

During development, the gonads in both sexes descend from their sites of origin on the posterior abdominal wall into the pelvic cavity in women and the developing scrotum in men. Before descent, a cord of tissue (the gubernaculum) passes through the anterior abdominal wall and connects the inferior pole of each gonad with primordia of the scrotum in men and the labia majora in women (labioscrotal swellings).

A tubular extension (the processus vaginalis) of the peritoneal cavity and the accompanying muscular layers of the anterior abdominal wall project along the gubernaculum on each side into the labioscrotal swellings.

In men, the testis, together with its neurovascular structures and its efferent duct (the ductus deferens) descends into the scrotum along a path, initially defined by the gubernaculum, between the processus vaginalis and the accompanying coverings derived from the abdominal wall.

Inguinal region development
Inguinal region development.
The inguinal canal is the passage through the anterior abdominal wall created by the processus vaginalis. The spermatic cord is the tubular extension of the layers of the abdominal wall into the scrotum that contains all structures passing between the testis and the abdomen. The distal sac-like terminal end of the spermatic cord on each side contains the testis, associated structures, and the now isolated part of the peritoneal cavity (the cavity of the tunica vaginalis).

In women, the gonads descend to a position just inside the pelvic cavity and never pass through the anterior abdominal wall. As a result, the only major structure passing through the inguinal canal is a derivative of the gubernaculum (the round ligament of uterus).

Pancoast’s Syndrome

•Bronchogenic carcinoma in the apex of the lung.
•Horner’s Syndrome: miosis, ptosis, enophthalmos and anhidrosis.
•Lower brachial plexus injury (C8-T1): Klumpke’s palsy.
•Paresthesia of the upper extremity due to compression of subclavian artery & vein.
•Shoulder pain: due to involvement of upper ribs and intercostal nerves.
•Respiratory effects.
The differential diagnoses of arm and shoulder pain are extensive; however, the primary conditions that must be excluded are thoracic outlet syndrome and cervical disk disease, which are commonly mistaken for Pancoast syndrome in the early clinical course. Careful neurologic examination, electromyographic studies, and ulnar nerve studies are performed to verify the precise diagnosis.
Diagram for Pancoast’s Syndrome.

Breast Density

Breast density, which is a representation in mammography of the amount of breast parenchyma present in the breast, can be assessed on MRI on both T2- and T1-weighted images. Breasts are characterized using BI-RADS (Breast Imaging Reporting and Data System) criteria:
1: almost entirely fatty;
2: scattered fibroglandular densities;
3: heterogeneously dense; and
4: extremely dense as with mammography

Unlike mammography, dense breasts generally do not pose a significant problem on MRI as contrast is used and thin slices are obtained, thus overlapping parenchyma is not a hindrance. There are, however, a small set of patients who exhibit very early rapid enhancement of the parenchyma, which can obscure small enhancing suspicious foci. In these cases, it may be helpful to communicate the lowered sensitivity of MRI to the referring physician.

(A) MLO Mammography image and (B) Contrast-enhanced MRI breast image.