Spleen

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CHAPTER 71 Spleen

The spleen consists of a large encapsulated mass of vascular and lymphoid tissue situated in the upper left quadrant of the abdominal cavity between the fundus of the stomach and the diaphragm. Its shape varies from a slightly curved wedge to a ‘domed’ tetrahedron. The shape is mostly determined by its relations to neighbouring structures during development. The superolateral aspect is shaped by the left dome of the diaphragm with the inferomedial aspect being influenced mostly by the neighbouring splenic flexure of the colon, the left kidney and stomach. Its long axis lies approximately in the plane of the tenth rib. Its posterior border is approximately 4 cm from the mid-dorsal line at the level of the tenth thoracic vertebral spine. Its anterior border usually reaches the mid-axillary line.

The size and weight of the spleen vary with age and sex. It can also vary slightly in the same individual under different conditions. In the adult it is usually 12 cm long, 7 cm broad, and 3–4 cm wide. It is comparatively largest in the young child, and although its weight increases during puberty, by adulthood it is relatively smaller in comparison to the neighbouring organs. It tends to diminish in size and weight in senescence. Its average adult weight is about 150 g, although the normal range is wide, between 80 g and 300 g, in part reflecting the amount of blood it contains. The normal-sized adult spleen fits comfortably in a cupped hand; the spleen has to be at least three times its normal size before it can be palpated.

Additional collections of fully functional splenic tissue may exist near the spleen, especially within the gastrosplenic ligament and greater omentum. These accessory spleens, or splenunculi, are usually isolated but can be connected to the spleen by thin bands of similar tissue. They may be numerous and widely scattered in the abdomen. The spleen may retain its fetal lobulated form or show deep notches on its diaphragmatic surface and inferior border in addition to those usually present on the superior border.

RELATIONS

The spleen has a superolateral diaphragmatic and an inferomedial visceral surface (Fig. 71.1). There are superior and inferior borders and anterior and posterior extremities or poles. The diaphragmatic surface is convex and smooth and faces mostly superiorly and laterally although the posterior part may face posteriorly and almost medially as it approaches the inferior border. The diaphragmatic surface is related to the abdominal surface of the left dome of the diaphragm which separates it from the basal pleura, the lower lobe of the left lung and the ninth to eleventh left ribs (Fig. 71.2). The pleural costodiaphragmatic recess extends down as far as its inferior border. The visceral surface faces inferomedially towards the abdominal cavity, and is irregular and marked by gastric, renal, pancreatic and colic impressions. The gastric impression faces anteromedially and is broad and concave where the spleen lies adjacent to the posterior aspect of the fundus, upper body and upper greater curvature of the stomach. It is separated from the stomach by a peritoneal recess, which is limited by the gastrosplenic ligament. The renal impression is slightly concave and lies on the lowest part of the visceral surface, separated from the gastric impression above by a raised strip of splenic tissue and the splenic hilum. It faces inferomedially and slightly backwards, being related to the upper and lateral area of the anterior surface of the left kidney and sometimes to the superior pole of the left suprarenal gland. The colic impression lies at the inferior pole of the spleen and is usually flat. It is related to the splenic flexure of the colon and the phrenicocolic ligament. The pancreatic impression is often small when present and lies between the colic impression and the lateral part of the hilum. It is related to the tail of the pancreas which lies in the splenorenal ligament. The hilum of the spleen is a long fissure pierced by several irregular apertures through which the branches of the splenic artery and vein as well as nerves and lymphatics enter and leave the spleen; it lies in the visceral surface closer to the inferior border and anterior border.

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Fig. 71.2 The posterior relations (‘bed’) of the spleen.

(Adapted from Drake, Vogl and Mitchell 2005.)

The superior border separates the diaphragmatic surface from the gastric impression and is usually convex. Near the anterior extremity there may be one or two notches that have persisted from the lobulated form of the spleen in early fetal life. However, they are often absent and are not a reliable guide to the identification of the spleen during clinical examination. The inferior border separates the renal impression from the diaphragmatic surface and lies between the diaphragm and the upper part of the lateral border of the left kidney. It is more blunt and rounded than the superior border and corresponds in position to the lower margin of the eleventh rib. The posterior extremity, or superior pole, usually faces the rounded vertebral column. The anterior extremity, or inferior pole, is larger and less angulated than the posterior extremity and connects the lateral ends of the superior and inferior borders: it is related to the colic impression and may lie adjacent to the splenic flexure and the phrenicocolic ligament.

PERITONEAL CONNECTIONS OF THE SPLEEN

The spleen is almost entirely covered by peritoneum that adheres firmly to its capsule, and is separated from the stomach and left kidney by recesses of the greater sac. It develops in the upper dorsal mesogastrium (see Figs 73.6 to 73.7), and remains connected via folds of peritoneum to the posterior abdominal wall (by the splenorenal, phrenicocolic and phrenicosplenic ligaments) and to the anterolateral abdominal wall and stomach (by the gastrosplenic ligament) (Fig. 71.3A). The splenorenal ligament is formed from two layers of peritoneum. The anterior layer is continuous with the peritoneum of the posterior wall of the lesser sac over the left kidney and with peritoneum of the splenic hilum where it runs into the posterior layer of the gastrosplenic ligament. The posterior layer of the splenorenal ligament is continuous with the peritoneum over the inferior surface of the diaphragm and runs onto the splenic surface over the renal impression. The splenic vessels lie between the layers of the splenorenal ligament: the tail of the pancreas is usually present in its lower portion (see Fig. 64.5B). The length of the splenorenal ligament may vary. Longer ligaments tend to make the spleen more mobile and may predispose the spleen to injury due to rotational shear forces during trauma, however they also make the mobilization of the spleen easier during surgery. The presence of the pancreatic tail within the splenorenal ligament must be remembered because it can be injured during ligation of the splenic vessels, causing pancreatitis or a pancreatic duct fistula to form.

The gastrosplenic ligament also has two layers (Fig. 71.3B). The posterior layer is continuous with the peritoneum at the splenic hilum and over the posterior aspect of the stomach. The anterior layer is formed from the peritoneum that is reflected off the gastric impression and reaches the greater curvature of the stomach anteriorly. The short gastric and left gastroepiploic branches of the splenic artery pass between its layers. Division of the gastrosplenic ligament during surgery may be hazardous if the ligament is short because ligation of the short gastric vessels may risk injury to the greater curvature of the stomach.

The phrenicocolic ligament extends from the splenic flexure of the colon to the diaphragm at the level of the eleventh rib. It extends inferiorly and laterally and is continuous with the peritoneum of the lateral end of the transverse mesocolon at the lateral margin of the pancreatic tail, and the splenorenal ligament at the hilum of the spleen.

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