While extensive previous references in the literature leave little doubt that disease in the posterior pararenal space can obliterate the psoas margin either in its entirety or in part, little work has been done to evaluate the frequency of when the psoas cannot be visualized in normal individuals. The data presented here indicate that as the right psoas can be expected to be absent in normal patients from 16 to 43% of the time, therefore one cannot `lean' heavily on it as a clinical tool.
On the other hand, absence of the left psoas margin on a single film in the proper clinical setting may be sufficient to draw one's attention to the retroperitoneal space, more particularly the posterior pararenal space, as a possible site of abnormality. However, ancillary radiographic signs such as mass displacement, gas, calcium, or abnormal depositions of fat, should be carefully sought.
Preservation of either or both psoas margins certainly does not exclude by any means significant extraperitoneal disease, as can be seen even in our small anecdotal series.
The hepatic angle is absent with such frequency in normal patients that it too can only be of questionable value as a primary radiographic sign. In our normal group of patients the splenic angle was absent more frequently than it was present.
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