Renal Fascia
The renal parenchyma is enclosed by
a thin but distinct glistening membrane known as the fibrous (true) capsule of
the kidney, which extends into the renal sinus. Immediately surrounding the
fibrous capsule is a variable amount of perinephric fat (perirenal fat capsule),
which forms a matrix around the structures within the renal sinus. The
perinephric fat also surrounds the ipsilateral suprarenal gland.
The kidneys, suprarenal glands, and perinephric fat are all contained
within a condensed, membranous layer of renal fascia. The renal fascia consists
of a stronger posterior and more delicate anterior layer, previously described
as two separate structures (posterior fascia of Zuckerkandl and anterior fascia
of Gerota) that fused laterally to form the lateral conal fascia. At present,
however, the renal fascia is regarded as a single structure.
The posterior layer originates from the lateral aspect of the psoas
fascia, fusing variably with the anterior layer of thoracolumbar fascia
(quadratus lumborum fascia) and transversalis fascia as it passes posterior and
lateral to the kidney. It then wraps around the anterior aspect of the kidneys
as the anterior layer. The medial continuation of the anterior layer ensheaths
the renal vessels and fuses with the sheaths of the abdominal aorta and
inferior vena cava. In some individuals, these fusions are very delicate and
may rupture under pressure, permitting midline crossing of accumulated fluid.
Another delicate fascial prolongation extends inferomedially along each ureter
as periureteric fascia.
There is substantial disagreement over the craniocaudal boundaries of the
renal fascia, reflecting its tenuous and elusive structure. In their cranial
aspect, the anterior and posterior layers are generally thought to fuse
superior to the suprarenal glands. In several studies this fused fascia appears
to define a closed space on each side, which is then continuous with the diaphragmatic
fascia in the region of the coronary ligament on the right and the
gastrophrenic ligament on the left.
Other studies, however, have challenged the notion that these spaces are
closed, finding the perinephric
space to be
continuous with the
bare area between liver and diaphragm
on the right and the subphrenic extraperitoneal space on the left.
Caudally, fusion of the anterior and posterior layers is incomplete,
which allows perinephric fluid to seep into the iliac fossa of the greater
pelvis. Likewise, air injected into the presacral space is known to reach the
perinephric space through this same opening; this technique was formerly used to visualize the kidneys in a
procedure known as retroperitoneal pneumography.
External to the renal fascia lies the retroperitoneal paranephric fat
(pararenal fat body), a continuation of the extraperitoneal fat. The perinephric
and paranephric fat are both traversed by variably developed strands of
collagenous connective tissue that extend from the renal fascia, which may
cause them to appear multilaminate in sectional studies.
