Ultrasound appearances

The normal spleen has a fine, homogeneous texture, with smooth margins and a pointed inferior edge. It has similar echogenicity to the liver (but may be slightly hypo- or hyperechoic in some subjects) but the echoes tend to be finer and more closely packed than the liver.

Sound attenuation through the spleen is less than that through the liver, requiring the operator to ‘flatten’ the TGC controls to maintain an even level of echoes throughout the organ.

The main splenic artery and vein and their branches may be demonstrated at the splenic hilum (Fig. 6.1). The spleen provides an excellent acoustic window to the upper pole of the left kidney, the left adrenal gland and the tail of the pancreas.

Fig. 6.1 • (A) Left coronal view of the normal spleen demonstrating vessels at the hilum.

(B) Left coronal view of the normal spleen at the hilum. The splenic artery (arrow) lies alongside the vein. The PRF is set for the lower, venous velocity so the artery demonstrates ‘aliasing’.

(C) By increasing the Doppler sensitivity, (decreasing the PRF) the perfusion within the spleen is demonstrated.

(D) An enlarged spleen can be displayed more fully using an extended field of view, allowing measurement of the length (25 cm). Shadowing from the ribs is evident.

Splenomegaly

Enlargement of the spleen is a highly non-specific sign associated with numerous conditions, the most common being infection, portal hypertension, haematological disorders and neoplastic conditions (Box 6.1).

As with the liver, measurement of splenic volume is unreliable and not reproducible, due to variation in shape and subdiaphragmatic access. However, the length of the spleen is an adequate indicator of size for most purposes and provides a useful baseline for monitoring changes in disease status. The length (infero-superior) of the normal adult spleen is less than 12 cm.

The spleen enlarges downwards and medially. Its inferior margin becomes rounded (Figs 6.1D, 6.2A) and it may extend below the left kidney and into the pelvis.

Fig. 6.2 • (A) Splenomegaly in portal hypertension. The inferior splenic margin is blunted, descending below and medial to the left kidney. Varices are present around the hilum.

(B) Varices, in the form of a spleno-renal shunt, in portal hypertension.

(C) A splenunculus (arrow) at the hilum of a mildly enlarged spleen.

(D) The circulation of the splenunculus derives from the main splenic artery and drains into the main splenic vein.

(E) The left lobe of the liver, LL, extends across the abdomen and above the spleen, S, in hepatomegaly, giving the appearance of a well-defined splenic ‘mass’.

Although the etiology of splenomegaly may not be obvious on ultrasound, the causes can be narrowed down by considering the clinical picture and by identifying other relevant appearances in the abdomen. Splenomegaly due to portal hypertension, for example, is frequently accompanied by other associated pathology such as cirrhotic liver changes, varices (Fig. 6.2A, B) or ascites (see Chapter 4).

Splenunculi

In around 10% of the population, a small accessory spleen, or splenunculus, may be located at the splenic hilum. These small, well-defined ectopic nodules of splenic tissue (Fig. 6.2C) rarely exceed 2 cm in diameter. Splenunculi enlarge under the same circumstances as those which cause splenomegaly, and may also hypertrophy in post-splenectomy patients.

The importance of recognizing these lies in differentiating them from lymph nodes, left adrenal nodules or masses in the tail of pancreas. Colour Doppler may identify the vascular supply as being common to the main spleen (Fig. 6.2D).¹

Pitfalls in scanning the spleen

Lymphoproliferative disorders

These are malignant haematologic conditions, comprising Hodgkin’s and non-Hodgkin’s lymphoma, leukaemias and myeloma.

Lymphoma is the most common malignant disease affecting the spleen (Fig. 6.3). Malignant cells can infiltrate the spleen, lymph nodes, bone marrow and thymus and can also involve the liver, gastrointestinal tract, kidney and other organs. Approximately 3% of malignant diseases are lymphomas.

Fig. 6.3 • Lymphoma:

(A) A hypoechoic focal lesion in a normal-sized spleen in a patient with AIDS is suspicious for lymphoma.

(B) Enlarged, coarse-textured spleen containing multiple tiny lymphomatous lesions.

(C) Extensive lymphadenopathy in the epigastric region.

(D) PTLD: (Di) hypoechoic focal lesions in a liver transplant; and (Dii) MRI of another case of PTLD.

Splenic involvement may be found in up to 60% of lymphomas as a result of dissemination of the disease. Primary splenic lymphoma, limited to the spleen, is very rare, and accounts for less than 1% of lymphomas.

Lymphoma is also associated with AIDS and infection with HIV has given rise to a broad spectrum of lymphomatous conditions which may be demonstrated on ultrasound and CT.² These include masses in the liver, spleen, kidneys, adrenal gland, bowel and other retroperitoneal and nodal masses. In addition, the increased use of immunosuppression in transplant patients, and the increased survival in this group, has also been the cause of an increased incidence of immunodeficiency-related lymphoma known as PTLD (Fig. 6.3D) (see also Chapter 4).

Clinical features and management

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Ultrasound of the acute abdomen Optimizing the diagnostic information The pancreas Pathology of the gallbladder and biliary tree Ultrasound of the renal tract Pathology of the liver and portal venous system

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