spleen in its typical position in the left upper quadrant of the abdomen (Fig. 73-1). In that location, the

spleen relates to the diaphragm both superiorly and laterally, and it generally spans the 9th, 10th, and

11th ribs along the left mid to posterior axillary line. The ventral surface of the spleen relates to the

greater curvature of the stomach and the tail of the pancreas. The tail of the pancreas touches the

splenic capsule in 30% of cases and is 1 cm away in 70% of cases. The inferior pole relates to the left

kidney posteriorly and the splenic flexure of the colon anteriorly.

The normal size of the spleen is approximately 13 × 7 × 4 cm.5 The typical weight of a spleen in a

young adult is felt to be 150 to 200 g and this decreases to approximately 100 g in the elderly

population (Fig. 73-2).7,8 It is felt that the spleen must double in size to the range of 300 to 400 g to

project below the costal margin to allow palpation of the spleen tip on abdominal examination in a

patient undergoing deep inspiration.9 The weight assigned to the spleen in defining massive

splenomegaly has been arbitrarily set at 1,500 g or 10 times the average adult splenic weight. There can

be a significant cleft in the capsule of the spleen that may be confused with splenic disruption on CT

scan obtained for trauma.

Figure 73-1. Anatomic relation of the spleen to the liver, diaphragm, pancreas, colon, and kidney. The stomach is sectioned to

illustrate the anatomic relation in situ.

1984

Figure 73-2. A: The lateral or diaphragmatic surface of the spleen, showing the lobulated edge and the glistening capsule. B: The

hilar surface of the spleen, showing the ligatures on the cephalad short gastric vessels and the caudal hilar vessels.

The vascular anatomy of the spleen is rather straightforward.10 The splenic artery is one of the three

major trunks along with the left gastric artery and common hepatic artery branching off from the celiac

axis (Fig. 73-3). This artery has a characteristic appearance on celiac arteriograms as a serpentine artery

with loops extending both superiorly and inferiorly. There are several small pancreatic branches that

supply blood to the body and tail of the pancreas along the lengths of this vessel. The first major splenic

branch occurs approximately 2 to 3 cm from the hilum and it is called the superior polar artery. The

main artery then divides into anywhere between three and five segmental branches that enter along the

trabeculae of the spleen. Additional blood supply to the spleen comes from the left gastroepiploic artery

via the short gastric vessels. When the spleen is massively enlarged, it may have direct vessels that are

parasitized from the omentum, diaphragm, or the mesentery of the splenic flexure of the colon. The

splenic artery generally travels outside the parenchyma of the pancreas just at the superior border

although loops that go inferiorly may be completely covered by the posterior surface of the pancreas

whereas superior loops may be well away from the pancreatic surface. It is these more cranially located

curves that are the optimal place to provide a ligature for control of the splenic artery during

procedures in which there is significant thrombocytopenia or for enlarged spleens. These are generally

areas that have few pancreatic branches and avoid proximity to the splenic vein that occurs when the

artery loops inferiorly.

The splenic vein is formed by segmental venous branches that leave the trabeculae and coalesce into

the main splenic vein in the hilum of the spleen (Fig. 73-3). The splenic vein is intimately associated

with the posterior surface of the tail and body of the pancreas to its junction with the superior

mesenteric vein forming the portal vein. The inferior mesenteric vein may join the splenic vein directly

at several areas along its course or may come together right at the junction of the superior mesenteric

vein. There are again several pancreatic branches that directly enter this splenic vein. The blood flow to

the spleen in the typical adult is estimated to be 200 to 300 mL/min or approximately 5% of the cardiac

output.10

The lymph node drainage generally follows the vasculature. The primary lymph nodes are located in

the hilum of the spleen and also along the splenic artery at the superior border of the pancreas and

along the short gastric vessels.

There are several ligaments that maintain the spleen in its fixed position in the left upper quadrant

(Fig. 73-4).6 Three of these ligaments are virtually always present (except in the condition of the

“wandering spleen”)11 and two may be present to variable extents, depending on the individual patient

and the disease process. The first ligament that is constant is the splenogastric ligament that is a leftsided superior extension of the greater omentum along the proximal greater curvature of the stomach.

Within this area supplied by the left gastroepiploic vessels are short gastric vessels that branch to the

1985

upper pole of the spleen and often provide the upper two-thirds of the spleen with alternative blood

supply. The second and very important ligament is the splenorenal ligament that runs parallel to the

posterolateral border of the spleen and attaches this to the superior pole of Gerota fascia developing the

left kidney. This ligament is divided when mobilizing the spleen during splenectomy and allows

reflection of the spleen with or without tail of the pancreas medially. The splenocolic ligament is short

and may be avascular or have small blood vessels that go from the inferior tip of the spleen to the

splenic flexure of the colon. This may be divided by cautery or may have vessels that need controlled

with ties or clips during mobilization of the splenic flexure of the colon.

Two ligaments that are variably present are the spleno- omental attachments and the splenophrenic

attachments (Fig. 73-4). The free part of the greater omentum may have variable association with the

splenic capsule along the inferior pole. There are often small vessels that may be controlled by

electrocautery. This attachment may be absent or may be quite extensive over the lower pole of the

spleen. It is this attachment to the omentum that often leads to disruption of the capsule along this

inferior pole causing bleeding in other abdominal procedures and may even eventually result in

splenectomy for control with an inadvertent injury. Before exerting inferior traction on the omentum

during any procedure, the extent of attachments to the lower pole of the spleen should be investigated

and, if present, should be divided prior to more vigorous mobilization. There may be direct ligaments

connecting the spleen to the diaphragm identified as splenophrenic ligaments. These typically are

present to a greater degree when the spleen is diseased or enlarged. They may be avascular or may

have branches of vessels parasitized from the diaphragm blood supply especially with large spleens.

Figure 73-3. The arterial blood flow to the spleen is derived from the splenic artery, the left gastroepiploic artery, and the short

gastric arteries (vasa brevia). The venous drainage into this portal vein is also shown.

The anatomy of the spleen itself is segmental being fed by arteries and drained by veins that leave via

the trabecula.12 The trabeculae are fibrous bands that attach to the splenic capsule. The parenchyma of

the spleen in between these trabeculae is divided into a small area of white pulp surrounding the

arteries, a marginal zone, and the larger predominant area of red pulp that comprises 75% of the splenic

parenchyma.13,14 The capsule of the spleen is quite thin as it is only a few cells layers thick. This

consists of a single layer of mesothelium and several layers of fibroelastic tissue. In other mammals but

not humans, there may be variable amounts of smooth muscle in the capsule. This smooth muscle would

allow contraction and mobilization of the circulating blood cells that are stored in the spleen.15 The

trabecular arteries that enter the spleen as continuation of the segmental arterial branches then give off

perpendicular branches to form the central arteries (Fig. 73-5). Surrounding these central arteries is the

1986

periarterial lymphatic sheath that is composed of T lymphocytes as well as follicles with B cells at

various stages of development. During the antigenic stimulation, this area greatly expands with more

mature and secondary follicles. The marginal zone is the borderline between the white pulp and the red

pulp and contains a mixture of lymphatics and macrophages. The structure of the red pulp is made up of

splenic cords with an intervening area called splenic sinuses. The splenic cords, also known as the cords

of Billroth, are a meshwork of fibroblasts and a large number of mature macrophages. The splenic

sinuses are an interconnective meshwork of fairly random red cell spaces that are thin walled and

generally filled with large numbers of erythrocytes.14

Figure 73-4. The relations of the spleen to the abdominal and retroperitoneal viscera are seen in a cross section of the left-facing

torso.

Figure 73-5. The splenic microanatomy is shown with depictions of both the open and closed circulations.

Studies on blood flow show two alternative routes to the spleen being fast flow and slow flow.16 A

small proportion of the blood goes through the splenic arteries and returns rapidly to the splenic veins.

This fast flow pattern consists of a greater predominance of plasma and few erythrocytes because of

streaming and accounts for only 10% of flow. A particularly large portion of the erythrocytes that enter

the spleen travel through the highly fenestrated meshwork in the red pulp as part of the filtration

process of the spleen. This slow path or slow flow comprises up to 90% of the splenic blood flow and

relates to the role of the spleen in clearly senescent erythrocytes.

2 Accessory spleens are small nodules of splenic tissue that are completely separate from the main

body of the spleen. They typically range in size from 0.5 cm up to 3–4 cm. The reported incidence of

accessory spleens ranges between 10% and 20%. The most common location for these small nodules of

splenic tissue is in the splenic hilum, the omentum most commonly between the stomach and transverse

colon but also within the greater omentum, and the small bowel mesentery. However, they can occur

virtually anywhere in the abdomen including the retroperitoneum behind the spleen and in the pelvis.

Accessory spleens are important in disease processes in which a complete removal of all splenic tissue is

mandatory for long-term cure such as certain autoimmune disorders. A preoperative nuclear medicine

spleen scan may also be helpful in some circumstances to identify sources of residual splenic tissue,17

1987