Abdominal x rays made easy: bones and soft tissues

In the fifth article in their series on how to read plain abdominal x ray films, Ian Bickle and Barry Kelly discuss inspecting bones and soft tissues and interpreting the findings

Often, little attention is paid to bones and soft tissues when reviewing an abdominal x ray film. However, careful inspection may find new, associated, or longstanding concomitant pathology. With concomitant pathology two abnormalities are identified but have no direct association--for example, an abdominal aortic aneurysm and a fracture of the femoral neck. So including bone and soft tissues as part of a systematic review ensures that no significant findings are overlooked (box 1).

Let's begin by reminding ourselves of the bones and soft tissues shown on an abdominal x ray film.

Anatomy

Bones include the lower ribs and their articulations, the lower thoracic and the lumbar spine, the bony pelvis, and the proximal femora. Soft tissues include the abdominal viscera and the surrounding muscle and soft tissues that envelop the lower trunk.

Pathology of the bone and soft tissues can be identified on abdominal x ray film for three main reasons: it may be new pathology, causing the symptoms that precipitated the abdominal x ray film, associated pathology, or concomitant pathology.

Bones

Bony pathology may be divided into local and generalised disease (box 2).

Generalised bone pathology

Osteoporosis can be identified as osteo-
penia when at least 15% of bone mass has been lost. It is commonly seen in the vertebral bodies, often coincidentally, in otherwise symptomless, postmenopausal women who are being investigated for other reasons. Its manifestation may also be as a vertebral wedge ("crush") fracture, leading to scoliosis and kyphosis see fig 1 (also see this month's Minerva picture, p 352).

Similarly, Paget's disease affects almost exclusively elderly people. In the spine, there is usually involvement of the vertebral body with coarsening and thickening of the trabeculae, bony enlargement, and sometimes an "ivory vertebra" (uniformly white, without contours). Another common site is the ileopectineal line of the pelvis (fig 1).

Fig 1: Scoliosis and kyphosis

Localised bone pathology

Localised Paget's disease may be difficult to distinguish from sclerotic metastases. A useful clue is that Paget's disease typically extends to the end of the bone whereas metastases are more randomly distributed. Sclerotic metastases are typical of prostatic carcinoma or lymphoma. Metastases are, however, more commonly lytic. These are destructive lesions; seen as areas of bony radiolucency, which appear as "dark" areas within a bone.

The term "lucent" or "lucency" is used to describe a focal area of bony osteopenia--for example, a bone cyst. The term "lytic" however implies a lucent lesion that appears infiltrative--for example, metastases or osteomyelitis. A lytic bony metastasis classically presents as an absent pedicle on the anterior view, the metastasis having destroyed the pedicle.

Metastases are one of the causes of fractures seen on abdominal x ray film. Fractures may be recent (and may be the immediate cause for the assessment) or old. Vertebral, femoral neck, rib, and pelvic fractures feature on the abdominal x ray film and may have relevance to other features on the film.

Primary bone disease seen on abdominal x ray film is usually a coincidental finding, often already recognised and cared for by other hospital specialists. In elderly people, osteoarthritis of both the spine and the femoral head are found often. Osteoarthritis of the femoral head has several well recognised radiographic features (box 3).

In younger patients, ankylosing spondylitis may affect the spine and the pelvis. Fusion of the sacroiliac joints precedes spinal involvement. This latter feature is described classically on radiographs as a bamboo spine, with evidence of syndosmophyte formation and calcification of the longitudinal spine ligaments (see Figs 2 and 3)

Soft tissues

The yield of positive radiographic findings involving the soft tissues is less than for bone. Calcification involving soft tissue structures was discussed in an earlier part of this series.¹ Alteration in size and shape of solid organs, such as the kidneys (box 4), liver, and spleen can be observed, as may the loss of their properitoneal fat lines. Furthermore, the loss of the psoas muscle shadows may indicate intraperitoneal disease (see Fig 4)

Fig 4: Absent left psoas muscle shadow

1. Bickle I, Kelly B. Abdominal x rays made easy: calcification. studentBMJ 2002;10:272-4. (August.)