British Journal of Radiology 74 (2001),767-772 © 2001 The British Institute of Radiology
CT findings in congenital anomalies of the spleen
G Gayer, MD
1
R Zissin, MD
2
S Apter, MD
1
E Atar, MD
1
O Portnoy, MD
1 and
Y Itzchak, MD
1
Departments of Diagnostic Imaging, 1The Chaim Sheba Medical Center and 2Sapir Medical Center, Affiliated to the Sackler Faculty of Medicine, Tel Aviv University, Israel
Correspondence: Dr G Gayer, Department ofDiagnostic Imaging, Sheba Medical Center, Tel Hashomer 52621, Israel
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Abstract
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There is a wide range of congenital anomalies of the spleen. Some are common, such as splenic lobulation and accessory spleen. Other less common conditions, such as wandering spleen and polysplenia, have particular clinical significance. Radiologists need to be aware of the various congenital variants of the spleen in order to recognize clinically important anomalies and to avoid mistaking less significant ones for an abnormality. In this pictorial review, the embryology of congenital anomalies of the spleen as well as their appearance on CT are described, diagnostic pitfalls are identified and complications of the anomalies are discussed.
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Introduction
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The spleen is included and well demonstrated on every CT of the abdomen. It is also often included on CT of the lower part of the chest. There is a wide spectrum of congenital anomalies, ranging from the common splenic lobulation and accessory spleen to rare conditions such as a wandering spleen and polysplenia. The majority of these anatomical variants have no clinical significance, although they need to be recognized as anatomical variants by the radiologist. On the other hand, a wandering spleen may rotate around its pedicle and present as an acute abdomen due to splenic infarction. Awareness of the various splenic congenital variants is important for the radiologist to interpret the findings correctly and to avoid mistaking them for an abnormality.
We review the embryology of congenital anomalies of the spleen as well as their appearance on CT, stress pitfalls and describe complications resulting from these anomalies.
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Splenic clefts, notches and lobulations
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The spleen begins to develop during the fifth week of fetal life from a mass of mesenchymal cells originating in the dorsal mesogastrium (Figure 1a
). Rotation of the stomach and growth of the dorsal mesogastrium translocate the spleen from the midline to the left side of the abdominal cavity (Figure 1b). Rotation of the dorsal mesogastrium establishes a mesenteric connection, the splenorenal ligament, between the spleen and the left kidney (Figure 1c). The gastrosplenic ligament is the portion of dorsal mesentery between the spleen and the stomach [1, 2]. The fetal spleen is lobulated, but these lobules normally disappear before birth [1]. Splenic lobulations may persist along the medial part of the spleen (Figure 2a). A persisting bulge or lobule of splenic tissue sometimes extends medially, anterior to the upper pole of the left kidney (Figure 2b). Less often, such a lobule lies partially posterior to the upper pole of the left kidney and displaces it anteriorly [3].
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Figure 1. Schematic cross-sections of the upper abdomen at different stages of embryonic development. L, liver; S, stomach; Sp, spleen. Modified from reference [1]. (a) At 5 weeks, the spleen, developing within the dorsal mesogastrium (DM), is in the midline. (b) At 8 weeks, the spleen and the stomach rotate to the left while the liver enlarges and rotates to the right. (c) A mature fetus. A short splenorenal ligament resulting from fusion of the dorsal mesogastrium with the posterior peritoneum. The gastrosplenic ligament is the portion of dorsal mesentery between the spleen and the stomach. 1, falciform ligament; 2, gastrohepatic ligament; 3, gastrosplenic ligament; 4, splenorenal ligament.
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Figure 2. Splenic lobulations in two different patients. (a) Typical lobulation along the medial aspect of the spleen. (b) A prominent lobule of splenic tissue (S) extends medially, anterior to the upper pole of the left kidney. It may be mistaken for a space-occupying lesion arising from the kidney. P, posterior.
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The notches or clefts on the superior border of the adult spleen are remnants of the grooves that originally separated the fetal lobules [1]. These clefts can be sharp and are occasionally as deep as 2–3 cm (Figure 3). They may be erroneously interpreted as splenic laceration in patients with abdominal trauma.
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Figure 3. Splenic cleft. A prominent cleft (arrow) between lobulations of the spleen. This anatomical variant may be mistaken for a laceration in traumatized patients.
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Accessory spleen
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One or more small splenic masses may develop in one of the peritoneal folds early in fetal life. An accessory spleen is present in about 10% of individuals, commonly situated near the hilum of the spleen or adjacent to the tail of the pancreas [1, 4]. However, an accessory spleen may also occur along the splenic vessels, in the gastrosplenic or splenorenal ligaments (Figure 4), within the pancreatic tail, in the wall of the stomach or bowel, in the greater omentum or the mesentery or even inthe pelvis and scrotum [5, 6]. Accessory spleens areusually about 1 cm in diameter, but vary frommicroscopic deposits not visible on CT to 2 cm or 3 cm in diameter [1, 3, 4].
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Figure 4. Accessory spleen in a less typical location as an oval mass (arrowhead) measuring 1 cm x 1.5 cm, posterior to the spleen, with attenuation identical to that of the spleen.
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An accessory spleen resembles a lymph node, both on CT and macroscopically [4]. It is round or oval and its attenuation is identical to that of splenic tissue, both before and after administration of contrast medium. When situated in an atypical location, an accessory spleen can mimic an enlarged lymph node as well as a tumour in the adrenal gland, pancreas, stomach or intestine, and even in the testis [6]. A mass in the splenic hilum that fails to enhance to the same degree as the splenic parenchyma should not be considered an accessory spleen (Figure 5).
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Figure 5. Varices medial to the spleen mimicking an accessory spleen. (a) Pre-contrast CT, showing an oval mass ( ), measuring 2 cm x 1.5 cm, medial to the spleen. Its attenuation on this unenhanced scan is similar to that of the spleen. (b) On post-contrast CT, the mass has enhanced to a greater degree than the splenic parenchyma and is therefore not an accessory spleen. (c) 2 cm caudal to (b). Multiple round masses of higher attenuation than the spleen and situated medial to the spleen represent typical varices (v). Note the large spleen, secondary to liver cirrhosis.
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An accessory spleen is an incidental finding of no clinical significance in most patients. Awareness of the presence of an accessory spleen is important in a patient evaluated by CT prior to splenectomy, as failure to remove it may result in persistence of the condition that indicated the need for splenectomy [4]. An accessory spleen may be of clinical importance as a source of "preservable" splenic tissue in cases of a ruptured primary spleen. An accessory spleen can be reliably identified by radionuclide imaging with technetium sulphur colloid if it is 2 cm or greater in diameter [5]. Complications involving an accessory spleen are rare and include torsion of a wandering accessory spleen [7] or bleeding caused by spontaneous rupture [8].
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Polysplenia
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Polysplenia is a complex congenital syndrome characterized by partial visceral heterotaxia (situs ambiguous) and concomitant levoisomerism (bilateral left-sidedness). It is associated with multiple, highly variable cardiovascular and visceral anomalies. The splenic mass is usually divided into fairly equally sized masses, varying in number from two to six and ranging from 1 cm to 6 cm in diameter, which together equal the mass of a normal spleen (Figure 6). Less often there may be several small spleens adjacent to either one or two large spleens (Figure 7). The location of the spleens is in either the left or right upper quadrant, along the greater curvature of the stomach [9]. A single bilobed spleen is a rare variant.
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Figure 6. Abdominal heterotaxia in a 30-year-old woman with polysplenia syndrome evaluated for fever and abdominal pain. There are two round splenules (S) of similar size in the right upper quadrant. The stomach (white arrow) is also right sided. The liver is in the midline and its two lobes are equal in size. The intrahepatic segment of the inferior vena cava (black arrow) is on the left of the aorta.
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Figure 7. Polysplenia syndrome in a 70-year-old manwith anaemia. Three round, soft tissue masses of different sizes () in the left upper quadrant are splenules.Note absence of the hepatic segment of theinferior vena cava (IVC). A dilated azygos vein (arrowhead) is situated in the right retrocrural space, reflecting azygos continuation of the interrupted IVC, a common anomaly in polysplenia syndrome.
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In addition to multiple spleens, there are often other abdominal anomalies including a right-sided stomach (Figure 6
), a midline or left-sided liver (Figure 6), malrotation of the intestine, a short pancreas and inferior vena cava anomalies. These should be recognized as part of a syndrome to avoid misinterpreting them as pathological processes [10].
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Wandering spleen
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Wandering or ectopic spleen refers to migration of the spleen from its normally fixed location in the left upper quadrant. The spleen is anchored in its normal position by two ligaments: the gastrosplenic ligament, which connects the greater curvature of the stomach to the ventral aspect of the spleen; and the splenorenal ligament between the left kidney and the spleen, attaching the spleen to the posterior abdominal wall [2, 11]. Failure of development of these ligaments results in a long splenic mesentery and an abnormally mobile spleen. Acquired factors that may increase splenic mobility include abdominal wall laxity, the hormonal effects of pregnancy and splenomegaly [11]. This anomaly is quite rare, with a reported incidence in several large series of splenectomies of less than 0.5%. Wandering spleens are mainly found in children [11] and in women aged 20–40 years [5]. The wandering spleen may be incidentally detected as an abdominal or pelvic mass. CT findings of a wandering spleen are absence of the spleen in its normal position with a location somewhere else in the abdomen or pelvis (Figure 8).
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Figure 8. Wandering spleen. A 26-year-old woman with vague abdominal pain and a palpable mid abdominal mass. (a) CT at the level of the upper abdomen shows the left kidney (K) in a high position and absence of the spleen in its normal anatomical location. The left lobe of the liver extends into the right upper quadrant. (b) A more caudal image shows the spleen (S) in the left mid abdomen, mimicking the appearance of a space-occupying lesion. (c) 4 years later, an image at the level of the pelvis shows the spleen has rotated and descended into the pelvis. (d) The spleen (S) extends into the lower pelvis and is adjacent to the bladder (B) and the uterus (U). An intrauterine device is present in the uterine cavity.
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The major complication of a wandering spleen is acute, chronic or intermittent torsion caused by its increased mobility. Symptoms and signs of splenic torsion are notoriously variable: chronic abdominal discomfort probably due to splenic congestion or ligamentous pressure, intermittent pain presumably due to spontaneous torsion and detorsion, and less often severe abdominal pain from acute torsion and infarction, which produce marked congestion and capsular stretching [5, 11, 12]. Physical examination may demonstrate a tender mass [11].
In cases of torsion, the wandering spleen is not only located in an abnormal position but shows additional CT findings: (1) a circular whorled structure of alternating bands of radiolucency and radiodensity, usually at the splenic hilum, representing the splenic vessels and surrounding fat of the twisted splenic pedicle (Figure 9a); (2) hyperdense intraluminal filling defects of the splenic vessels on a pre-contrast scan (Figure 9a) and no enhancement of the vessels on a post-contrast scan in acute thrombosis; and (3) partial or total failure of the spleen to enhance with iv contrast medium, indicating infarction (Figure 9b). Contrast enhanced CT in these cases provides information concerning the viability of the splenic parenchyma. This information is valuable in deciding whether splenopexy rather than splenectomy is an option, especially in young children [11].
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Figure 9. Torsion of a wandering spleen. A 29-year-old woman with severe abdominal pain for 48 h and a history of bouts of abdominal pain since childhood. (a) On a pre-contrast image of the upper abdomen, the spleen is absent although splenic vessels (arrow) are seen in the left upper abdomen. These vessels have a whorled appearance with a hyperdense centre, compatible with a twisted splenic pedicle and fresh thrombus in the splenic vessels. (b) On a post-contrast image the torsioned spleen (S) lies in the left mid abdomen and shows no enhancement.
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Received for publication June 23, 2000.
Revision received September 20, 2000.
Accepted for publication November 16, 2000.
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Abstract
Introduction
