The wandering spleen is a disorder characterized by laxity of the suspensory splenic ligaments, which allows the spleen to lie in an ectopic location. Clinical findings range from an asymptomatic abdominal mass or intermittent abdominal pain (secondary to torsion and detorsion of the splenic pedicle) to an acute surgical abdomen (consequent to torsion of the splenic pedicle and vascular compromise). The imaging findings consist of absence of splenic tissue in the left upper quadrant and a mass elsewhere in the abdomen with a shape and architecture similar to normal spleen (Fig. 6.1) (7,8). The echotexture, attenuation, and signal intensity are similar to normal spleen. Findings of ascites, a twisted splenic pedicle, and a whorled appearance of the pancreatic tail and supporting fat indicate superimposed torsion. A focal hypoechoic lesion on sonography or nonenhancing lesion on CT suggests associated infarction (Fig. 6.2).

Accessory spleens are a common anatomic variant. They usually are clinically insignificant, except in patients who have had prior splenectomies for hematologic diseases. In these patients, the accessory splenic tissue can hypertrophy, resulting in recurrent hypersplenism. Most accessory spleens are located near the splenic hilum, but they also may be found along the splenic vessels or in the pancreatic tail. They are generally single, but about 10% are
multiple. Accessory spleens are usually smooth, round, or ovoid in shape and 2 to 3 cm in diameter (Fig. 6.3). They tend to have an echotexture, attenuation, and signal intensity similar to normal spleen.

Splenosis is the result of splenic rupture secondary to trauma or surgery with subsequent autotransplantation of splenic tissue. The peritoneal cavity is the most common site of splenosis, but splenic tissue can be found elsewhere in the abdomen or chest. On imaging studies, the splenic nodules in splenosis are round masses that are indistinguishable from accessory spleens. The masses in splenosis are distributed throughout the peritoneum and
the retroperitoneum, whereas accessory spleens are usually found in the left side of the abdomen near the splenic hilum.

Polysplenia and asplenia are both associated with cardiac and pulmonary abnormalities along with visceral heterotaxy (9). Polysplenia is characterized by multiple splenic nodules, which can be located in the right or left upper quadrants (Fig. 6.4). Associated abdominal anomalies include a transverse liver, interruption of the inferior vena cava with azygous continuation, short pancreas, abnormal rotation of the bowel, and renal agenesis or hypoplasia. Thoracic anomalies include bilateral left lungs, partial anomalous pulmonary venous return, and cardiac anomalies, including atrial and ventricular septal defects, transposition of the great vessels, and pulmonary stenosis or atresia.

Asplenia is characterized by absence of splenic tissue. Associated abdominal anomalies include total or partial sinus inversus, intestinal malrotation, and renal anomalies. Thoracic anomalies include bilateral morphologic right lungs and complex cyanotic heart lesions, including single ventricle, transposition of the great vessels, and total anomalous pulmonary venous drainage.

Hemangiomas are composed of vascular channels lined by a single endothelial layer and filled with red blood cells. They may be an isolated lesion or part of a syndrome, including Klippel-Trenaunay-Weber (characterized by capillary port-wine stains, varicosities, hypoplastic lymphatics, and lymphangiomas) and Beckwith-Wiedemann syndrome (characterized by prenatal and postnatal overgrowth, macroglossia, anterior abdominal wall defects, and hemihypertrophy).

The imaging appearance of hemangioma in the spleen is similar to that in the liver. The lesions are either hypoechoic or hyperechoic relative to normal splenic parenchyma on sonography (Fig. 6.7), hypoattenuating on precontrast CT, hypointense on T1-weighted images, and hyperintense on T2-weighted and fat-suppressed images (11). After administration of iodinated contrast or gadolinium, hemangiomas typically show centripetal enhancement with progressive central fill-in. Small lesions may show early uniform fill-in without centripetal opacification, whereas very large lesions may demonstrate persistent central hypoattenuation or hypointensity due to areas of fibrosis or thrombosis (Fig. 6.8). Peripheral or central calcifications can be seen in some cases.

Lymphangiomas are congenital malformations of the lymphatic system (12) and may be solitary or multiple (lymphangiomatosis). On all imaging studies, they appear as multilocular masses. The fluid-filled locules are hypoechoic or anechoic on sonography, hypoattenuating on CT, hypointense on T1-weighted images, and hyperintense on T2-weighted and fat-suppressed images (Fig. 6.9). After administration of iodinated contrast or gadolinium, the cystic areas do not enhance, whereas the septa may show some enhancement.

Splenic hamartomas are benign, solid lesions consisting of an admixture of normal splenic elements and disorganized congested splenic sinuses (red pulp). They have been associated with Beckwith-Wiedemann syndrome and tuberous sclerosis. Relative to normal splenic tissue, hamartomas appear hypoechoic on sonography, hypo- or isoattenuating on precontrast CT scans, isointense on T1-weighted image, and hyperintense on T2-weighted and fat-suppressed images. They show mild to moderate, heterogeneous enhancement after intravenous contrast or gadolinium administration (Fig. 6.10).