The Psoas Muscle

I have clarified the radiographic anatomy of the psoas muscle by anatomic sections through the extraperitoneal tissues at different levels.8 The upper and lower segments of the psoas muscle are visualized by virtue of the contrast provided by different aspects of the extraperitoneal fat.

At the level of the kidney, it is the perirenal fat that predominantly marginates the lateral border of the psoas muscle. However, below the kidney, secondary to the lines of fusion of the cone of renal fascia, posterior para-renal fat provides the contrast margination of the muscle.

Loss of visualization of the complete muscle border is often misleading and must be carefully evaluated. It is often not seen unilaterally in normal individuals.4,5 Furthermore, the psoas outline may disappear with only very minimal rotation or scoliosis of the lumbar spine,64 and extraperitoneal fat may be scanty in emaciated patients or in those who have lost weight.

A reliable sign, however, is segmental loss of visualization of the psoas border. Such asymmetry in properly centered films immediately localizes a fluid collection to a specific extraperitoneal compartment. Thus, localized perirenal processes tend to obliterate only the upper margin, whereas fluid collection in the posterior par-arenal spaces obliterates the psoas muscle in its lower segment (Fig. 8-38) or throughout, depending on its extent. Two qualifications must be appreciated: (a) on frontal films, a large collection within the anterior par-arenal space may, by superimposition of the density, obscure the psoas border, but well-penetrated oblique projections will nevertheless demonstrate its intact mar-

Fig. 8—34. Localized retraction of the thickened renorenal septum (arrow) at the site of a cortical scar. The renal fascia is also thickened (open arrows). (Courtesy of Michiel Feldberg, M.D., University of Utrecht, The Netherlands.)

Renorenal Bridging SeptumScarring The Psoas Muscle

Fig. 8—35. Perirenal bridging septa.

(a-c) CT shows the posterior lamella (arrows) over a vertical extent of 4.5 cm.

Fig. 8—36. Bridging renal septa.

(a) Among multiple bridging septa, the most conspicuous is a dorsal renorenal septum (arrows). These are associated with a thickened anterior renal fascia (open arrow).

(b) At a level below the lower renal pole, the septa continue within the fat in the cone of fascia.

Fig. 8—36. Bridging renal septa.

(a) Among multiple bridging septa, the most conspicuous is a dorsal renorenal septum (arrows). These are associated with a thickened anterior renal fascia (open arrow).

(b) At a level below the lower renal pole, the septa continue within the fat in the cone of fascia.

Fig. 8—37. Lymphatic stranding through the extraperitoneal spaces.

In a patient with non-Hodgkin's lymphoma with gross paraaortic/ paracaval adenopathy, CT demonstrates extraperitoneal lymphedema with thickening of fasciae and septa.

Lypoma Assiociated With Lymphedema

gin; (b) extraperitoneal gas localized within the posterior pararenal compartment will sharply outline the lateral border of the psoas muscle at all levels.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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