The spleen is a dark purplish, highly vascular, coffee bean–shaped
organ of mesodermal origin situated in the left upper quadrant of
the abdomen at the level of the 8th to 11th ribs between the fundus
of the stomach, the diaphragm, the splenic flexure of the colon,
and the left kidney (Figure 27–1).
The adult spleen weighs 100–150 g, measures about 12 × 7 × 4
cm, and usually cannot be palpated. It is attached to adjacent viscera,
the abdominal wall, and the diaphragm by peritoneal folds or “ligaments.” The
gastrosplenic ligament carries the short gastric vessels. The other
ligaments are avascular except in patients with portal hypertension
Normal anatomic relations of the spleen.
The splenic capsule consists of peritoneum overlying a 1- to
2-mm fibroelastic layer that contains a few smooth muscle cells.
The fibroelastic layer sends into the pulp numerous fibrous bands
(trabeculae) that form the framework of the spleen. Corrosion cast
studies demonstrate that the spleen consists of specific segments
based on arterial supply numbering between two and six separated
by an avascular plane.
The splenic artery enters the hilum of the spleen, branches into
the trabecular arteries, and then branches into the central arteries
that course through the surrounding white pulp and send radial branches
to the peripheral marginal zone and the more distant red pulp. The
white pulp consists of lymphatic tissue including T cells adjacent
to the central artery (periarteriolar lymphoid sheets [PALS]), with
a surrounding area containing lymphoid follicles rich in B cells
interspersed with dendritic and reticular cells important in antigen
presentation. The vascular spaces of the marginal zone between the
red and white pulp channel blood into the splenic Billroth cords
and out to the associated sinuses. The red pulp vascular structures
have a noncontiguous basement membrane that filters cells such as
senescent erythrocytes into the macrophage-lined sinuses.
Accessory spleens (splenunculi) are seen in 10–15% of
the normal population and are located primarily in the gastrosplenic,
gastrocolic, and lienorenal ligaments, but they can also be found throughout
the peritoneal cavity in the omentum, bowel mesentery, and pelvis. Accessory
spleens probably result from a failure of infusion of splenic embryologic
tissues. Ordinarily of no significance, they may play a role in
recurrence of certain hematologic disorders for which splenectomy
is performed. Removal of accessory spleens may lead to remission
of disease in these patients. Accessory spleens are more difficult
to identify with laparoscopic procedures, but the use of a hand
port has allowed identification and resection of accessory spleens
with a minimally invasive approach. Patients who fail to respond
to initial splenectomy should undergo scanning with technetium 99m-labeled
red cells or indium 111-labeled platelets to identify potential
sites of missed accessory spleens and can be identified intraoperatively
with a handheld gamma counter.
Ectopic spleen (wandering spleen) ...