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//PERIRENAL FASCIA

PERIRENAL FASCIA

The perirenal fascia is a dense, elastic connective tissue sheath which envelops each kidney and suprarenal gland together with a layer of surrounding perirenal fat (Fig. 74.4A,B; see Fig. 62.1). The kidney and its vessels are embedded in perirenal fat, which is thickest at the renal borders and extends into the renal sinus at the hilum.

  

Fig. 74.4  A, Sagittal section through the posterior abdominal wall showing the relations of the renal fascia of the right kidney. B, Transverse section, showing the relations of the renal fascia.

The perirenal fascia was originally described as being made up of two separate entities, the posterior fascia of Zuckerkandl and the anterior fascia of Gerota, which fused laterally to form the lateral conal fascia. According to this view, the lateral conal fascia continued anterolaterally behind the colon to blend with the parietal peritoneum. However, work by Mitchell (1950) showed that the perirenal fascia is not made up of distinct fused fasciae, but is in fact a single multilaminated structure which is fused posteromedially with the muscular fasciae of psoas major and quadratus lumborum. It then extends anterolaterally behind the kidney as a bilaminated sheet, which at a variable point divides into a thin anterior lamina, passing around the front of the kidney as the anterior perirenal fascia, and a thicker posterior lamina which continues anterolaterally as the lateral conal fascia, fusing with the parietal peritoneum.

Classically, the anterior perirenal fascia was thought to blend into the dense mass of connective tissue surrounding the great vessels in the root of the mesentery behind the duodenum and pancreas, thereby preventing communication between perirenal spaces across the midline. However inspection of CT images or of anatomical sections of cadavers, following injection of contrast or coloured latex respectively, into the perirenal space, revealed that fluid could extend across the midline at the third to fifth lumbar levels through a narrow channel measuring 2–10 mm in AP dimension. In the midline superiorly, the anterior and posterior renal fasciae fuse and are attached to the crura of their respective hemidiaphragms. Inferiorly the fasciae separate for a variable craniocaudal distance. The posterior perirenal fascia fuses with the muscular fascia of psoas major while the anterior perirenal fascia extends across the midline in front of the great vessels and so communication between the two sides is permitted although very rarely of clinical significance. Below this level the two fasciae once again merge and are attached to the great vessels or iliac vessels. The containment of fluid to one side of the perirenal space that is observed in over two thirds of clinical cases is attributed to the presence of fibrous septae.

Above the suprarenal glands the anterior and posterior perirenal fasciae were previously said to fuse with each other and to the diaphragmatic fascia. This description of a closed superior cone is not universally accepted. Cadaveric experiments have shown the superior aspect of the perirenal space to be open and in continuity with the bare area of the liver on the right and the subphrenic extraperitoneal space on the left. The posterior fascial layer blends bilaterally with the fascia of psoas major and quadratus lumborum as well as the inferior phrenic fascia. The anterior fascial layer on the right blends with the right inferior coronary ligament at the level of the upper pole of the kidney and bare area of the liver. On the left the anterior layer fuses with the gastrosplenic ligament at the level of the suprarenal gland.

There is some debate concerning the inferior fusion of the perirenal fascia. Many investigators believe that inferiorly the anterior and posterior leaves of the perirenal fascial fuse to produce an inverted cone which is open to the pelvis at its apex. Laterally the anterior and posterior leaves fuse with the iliac fascia, and medially they fuse with the periureteric connective tissue. The inferior apex of the cone is open anatomically towards the iliac fossa but rapidly becomes sealed in inflammatory disease. An alternative view is based on the dissection of recently deceased cadavers after injections of coloured latex into the perirenal space: these have shown that the anterior and posterior perirenal fasciae merge to form a single multilaminar fascia which contains the ureter in the iliac fossa. Anteriorly this common fascia is loosely connected to the parietal peritoneum, and so denies free communication between the perirenal space and the pelvis, and also denies communication between the perirenal and pararenal spaces.

A simple nephrectomy for benign disease removes the kidney from within perirenal fascia; a radical nephrectomy (for cancer) removes the entire contents of the perirenal space including the perirenal fascia, in order to give adequate clearance around the tumour.

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