Ultrasonography of The Spleen

In ultrasonography of the spleen, a focused beam of high-frequency sound waves passes into the left upper quadrant of the abdomen, creating echoes that vary with changes in tissue density. These are displayed on a monitor as real-time images that indicate the size, shape, and position of the spleen and surrounding viscera.

Ultrasonography is indicated in patients with an upper left quadrant mass of unknown origin; with known splenomegaly, to evaluate changes in splenic size; with left upper quadrant pain and local tenderness; and with recent abdominal trauma.

Purpose

• To demonstrate splenomegaly
• To monitor progression of primary and secondary splenic disease and to evaluate effectiveness of therapy
• To evaluate the spleen after abdominal trauma
• To help detect splenic cysts and subphrenic abscess

Patient preparation

• Explain to the patient that this procedure allows examination of the spleen.
• Tell him who will perform this test and where, that the room may be darkened slightly to aid visualization on the monitor, and that this procedure takes approximately 15 to 30 minutes.
• Instruct him to fast for 8 to 12 hours before the procedure, if possible; this reduces the amount of gas in the bowel, improving the transmission of sound waves.
• Describe the procedure and assure him that he'll feel only mild pressure.
• Instruct him to remain as still as possible during the procedure and to hold his breath when requested, to aid visualization.

Procedure and posttest care

• Because the procedure for ultrasonography varies, depending on the size of the spleen and the patient's physique, the patient is usually repositioned several times; the transducer scanning angle or path is also changed.
• Generally, the patient is first placed in a supine position, with his chest uncovered.
• A water-soluble conductive gel is applied to the face of the transducer, and transverse scans of the spleen are taken at 3/8" to 3/4 " (1- to 2-cm) intervals.
• The patient is then placed in a right lateral decubitus position, and transverse scans are taken through the intercostal spaces using a sectoring motion.
• A pillow may be placed under the patient's right side to help separate the intercostal spaces, making it easier to position the transducer face between them.
• Longitudinal scans are taken from the axilla toward the iliac crest.
• To prevent rib artifacts and to obtain the best view of the splenic parenchyma, oblique scans are taken by passing the transducer face along the intercostal spaces.
• During each scan, the patient may be asked to hold his breath briefly at various stages of inspiration.
• Good views are photographed for later study.
• Remove the conductive gel from the patient's skin.
• Inform the patient that he may resume his usual diet.

Normal findings

The splenic parenchyma normally demonstrates a homogeneous, low level echo pattern; its individual vascular channels aren't usually apparent. The superior and lateral splenic borders are clearly defined, each having a convex margin. The undersurface and medial borders, in contrast, show indentations from surrounding organs (stomach, left kidney, and pancreas).

The hilar region, where the vascular pedicle enters the spleen, commonly produces an area of highly reflective echoes. The medial surface is generally concave, which helps differentiate between left upper quadrant masses and an enlarged spleen. Even when splenomegaly is present, the spleen generally remains concave medially unless a space-occupying lesion distorts this contour.

Abnormal findings

Ultrasonography can show splenomegaly, but it usually doesn't indicate the cause; a computed tomography (CT) scan can provide more specific information. Splenomegaly is generally accompanied by increased echogenicity. Enlarged vascular channels are commonly visible, especially in the hilar region. If space-occupying lesions distort the splenic contour, liver-spleen scanning should be performed to confirm splenomegaly.

Abdominal trauma may result in splenic rupture or subcapsular hematoma. In splenic rupture, ultrasonography demonstrates splenomegaly and an irregular, sonolucent area (the presence of free intraperitoneal fluid); however, these findings must be confirmed by arteriography. In subcapsular hematoma, ultrasonography shows splenomegaly, as well as a double contour, altered splenic position, and a relatively sonolucent area on the periphery of the spleen. The double contour results from blood accumulation between the splenic parenchyma and the intact splenic capsule. As the spleen enlarges, a transverse section shows its anterior margin extending more anteriorly than the aorta. Ultrasonography may be difficult and painful after abdominal trauma because the transducer may have to pass across ftactured ribs and contusions; CT scanning, which differentiates blood and fluid in the peritoneal space, should be used instead.

In subphrenic abscess, ultrasonography shows a sonolucent area beneath the diaphragm. Clinical findings may differentiate between abscess and blood or fluid accumulation.

Used with liver-spleen scanning, ultrasonography differentiates cold spots as cystic or solid lesions. It shows cysts as spherical, sonolucent areas with well-defined, regular margins with acoustic enhancement behind them. When ultrasonography fails to identify a cyst as splenic or extrasplenic - especially if the cyst is located in the upper pole of the left kidney and the adrenal gland, or in the tail of the pancreas - a CT scan and arteriography are used. Ultrasonography can readily clarify cystic cold spots, but using a CT scan with a contrast medium is superior for evaluating primary and metastatic tumors. Ultrasonography usually fails to identify tumors associated with lymphoma and chronic leukemias because these resemble tumors of the splenic parenchyma.

Interfering factors

• Overlying ribs, aerated left lung, gas or residual barium in the colon or the stomach (possible poor imaging)
• Deficiency of body fluids in a dehydrated patient, obscuring boundaries between organs and tissue structures (possible poor imaging)
• Physique affecting the spleen's shape or adjacent masses displacing the spleen (possible poor imaging, may be mistaken for splenomegaly)
• Patient with splenic trauma (possible difficulty in tolerating the procedure)