cal typing. This is somewhat fraught with problems since, for instance, splenic cysts may be demonstrated as being anechoic, hypoechoic, or also hyperechoic. Therefore, an additional classification according to the frequency of diagnosis has been introduced.

Anechoic Mass

Dysontogenetic Cysts

Pseudocysts

Infective Cysts

True splenic cysts are characterized by an epithelial lining and are congenital in origin. On ultrasound, they appear as round, smooth, anechoic lesions, well-defined from the surrounding splenic texture, with signs of distal acoustic enhancement. Sometimes echogenic septation, internal echoes, sedimentation phenomena, sequestered tissue, and calcification of the wall may be observed. The contents of

the cyst may be watery clear or dark brown as a result of hemorrhage. In other cases the lumen of the (pseudo-)cyst is filled with pulpy material. On ultrasound, the fluid within the cysts is at times visualized with a floating, moving hyperechoic mass (“snowstorm”), corresponding to cell conglomerates, sequestered tissue, or crystals ( 5.3).

This may complicate differentiation from a solid mass. There are no certain sonographic signs ruling out pseudocysts. In 52 patients with noninfective splenic cysts (24 true cysts and 28 pseudocysts) there was no significant difference regarding size, intrinsic echogenicity, or contents of the cyst. Only calcification of the wall appeared to be more frequent in pseudocysts.

By definition, pseudocysts are not lined with epithelium. Almost without exception they are solitary lesions and, as such, sequelae to liquefactive, hemorrhagic, or encapsulating processes after pancreatitis, splenic trauma ( 5.4b,c), infarction ( 5.4a,g,h), and metastasis (see 5.10). Since splenic trauma and infarction are somewhat common, the percentage of secondary cysts (ca. 80%) is not only far larger than that of primary cysts (ca. 20%), but also larger than for other parenchymal organs (e. g., the liver).

General treatment of splenic cysts depends on the clinical symptoms, which in turn are a function of the size of the cyst. Cysts with a diameter of less than 5 cm should be followed up. Large lesions occupying the spleen are mostly treated by surgery, even today when conservative procedures are increasingly preferred. Ultrasound-guided catheter drainage with sclerosing agents is becoming a more viable option. Rupture and carcinoma of splenic cysts have been reported in a few rare cases.

Table 5.3 lists other rare anechoic splenic masses ( 5.4 d–f,i).

Table 5.3 Differential diagnosis of anechoic splenic masses

Infective cysts are rare and are encountered in less than 2% of all patients infected with hydatid disease. In most cases the infective agent is

Echinococcus cysticus or E. granulosus.

Most cysts are visualized as anechoic lesions with a double wall (pericyst and endocyst). In rare cases they may demonstrate daughter cysts. In exceptional cases these secondary cysts may be very small and numerous; and, because of the large number of wall echoes (Fig. 5.26), the sonographic appearance of such a hydatid cyst may resemble that of a hyperechoic lesion. Intracystic membranes, hydatid sand (scolicial sedimentation), and calcification have been reported. In general, the ultrasound appearance of infective splenic cysts is quite characteristic, although sometimes they are hard to differentiate from incidental splenic cysts. When there is doubt, the diagnosis has to be confirmed by laboratory work-up.

Fig. 5.26 Anechoic mass with festoon-like structures corresponding to a hydatid cyst. K = kidney.

Hypoechoic Mass

Invasive Lymphoma

Splenic Infarction

Splenic Abscess

Splenic Trauma

Splenic Metastasis

Splenic involvement may generally be diagnosed sonographically by the presence of splenomegaly (primarily in low-grade lymphoma) or the demonstration of hypoechoic focal or diffuse textural lesions of the splenic parenchyma. However, splenic involvement cannot be ruled out with certainty even if the spleen is of normal size and homogeneous texture.

Ultrasound differentiates between five different patterns of invasion (Fig. 5.27), with micronodular and macronodular invasion as well as the bulky formation corresponding to focal parenchymal lesions.

Diffuse splenic involvement. As in all parenchymal organs, the greatest difficulty ultrasound faces is with diffuse splenic involvement, and this is the main reason for the poor sensitivity (albeit for all imaging modalities) in diagnosing possible invasion of the spleen. Compared with the adjacent liver, a normal spleen will appear to be somewhat more homogeneous. The (subjective or operator-de- pendent) assessment of the splenic texture should be based on the liver as an in-vivo reference ( 5.5a–c).

Focal parenchymal lesions. The value of ultrasonography in the detection of focal parenchymal lesions is well known; it has a sensitivity of more than 90% and a specificity of 96%. Since the general incidence of focal splenic destruction is low, hypoechoic splenic masses in patients with lymphoma have to be regarded as neoplastic with a high degree of certainty (

5.5 d–g).

Frequently, large lesions will display an inhomogeneous echo texture ( 5.5h,i) with hyperechoic areas. Calcification is rare and will occur mostly after treatment.

Corresponding with the macroscopic findings, low-grade non-Hodgkin lymphoma as well as Hodgkin lymphoma tend toward diffuse or micronodular invasion, whereas highgrade non-Hodgkin lymphoma will lead to larger masses.

Perisplenic invasion. Perisplenic invasion by lymphoma is extremely rare; it may originate at the hilum and spread in caplike fashion ( 5.5j). Perisplenic invasion is also possible by the lymphoma spreading from the thorax through the diaphragm into the capsule of the spleen. In individual cases this may result in complications such as hemorrhage, rupture ( 5.5k,l), and infarction of the spleen.

Hypoechoic perivascular structural transformation. Hypoechoic perivascular structural transformation of the hilar vessels of the spleen is a rare entity in patients with malignant lymphoma. The etiology is unknown and it resolves under chemotherapy. Similar changes have been reported in the liver as hypoechoic structural lesions encompassing the portal vein (“periportal cuffing”). They have also been ob-

served in systemic hematological malignancy as well as in benign disorders. Apart from invasion by the lymphoma, perivascular edema

Fig. 5.27 Schematic illustration of the different sonographic patterns of splenic invasion in malignant lymphoma.

by lymphatic obstruction has also been suggested as one possible explanation (

5.5 m–o).

Sickle-cell anemia. In homozygous sicklecell anemia, oxygen deficiency and/or acidosis will lead to abnormal crystallization of hemoglobin with subsequent erythrocyte adhesion and manifestation of splenic infarction. This complication is less common, but still possible, in carriers (heterozygous sickle-cell anemia).

Thrombophilia. Congenital or acquired thrombophilia (e. g., congenital protein C or S deficiency, lupus anticoagulant, erythropoietin therapy) is an infrequent cause of splenic infarction.

Partial splenic dearterialization. Some children with thalassemia major undergo therapeutic partial dearterialization of the splenic artery with subsequent splenic infarction. In myeloproliferative disorder, hypersplenism may be palliated by embolization of branches of the splenic artery.

increasing atrophy of the organ, corresponding to autosplenectomy ( 5.2). In color-flow Doppler scanning of the scarred spleen, circulation in the organ is markedly reduced.

Total splenic infarction. Infarction of the entire spleen may be the result of acute splenic vein thrombosis in the wandering spleen, torsion of the vascular pedicle, acute sequestration in

homozygous childhood sickle-cell anemia, septic disorders, disseminated intravascular coagulation (DIC), or as part of pancreatitis ( 5.6j–l). The sonographic image is characterized by hypoechoic inhomogeneous transformation of the entire splenic texture.

Healing phase. Increasing echogenicity and shrinking size of the infarct characterize the healing phase. Sometimes local textural inhomogeneity or calcification will remain as a scar. In 80% of cases the infarction will heal without any complication ( 5.6h,i).

Complications. Twenty percent of patients will suffer complications, including:

●Increasing liquefaction of the infarct (

5.7a–c)

●Development of subcapsular hemorrhage ( 5.7 d–f)

●Flow phenomena identifiable on color-flow Doppler scanning and also by CEUS as indication of pseudoaneurysm or arteriovenous fistula ( 5.7 g–l)

●Demonstration of free intraperitoneal fluid (blood) ( 5.7 m,n)

Splenic Abscess

Microabscess. This is usually pyogenic. On ultrasound, a macroabscess is visualized as a smooth or irregularly shaped, primarily hypoechoic lesion that is delineated from the normal parenchymal texture. However, as for hepatic abscess, there is a wide spectrum of ultrasound morphology of these splenic abscesses, which can be traced back to the difference in the number of acoustically relevant echo boundaries. These morphologies include:

●Completely anechoic abscess resembling a cyst with posterior acoustic enhancement

●Hypoechoic abscess with different degree of textural echo pattern ( 5.8a–c)

●Markedly hyperechoic abscess, sometimes gaseous, with or without posterior acoustic enhancement (Fig. 5.29)

Differentiating splenic abscess from other focal masses (hematoma, infarct, cyst, tumor) by ultrasound criteria for contour and texture alone, not taking into account any clinical parameters, is fraught with problems. Since splenic abscess has a mortality of up to 100% if left untreated, a tentative diagnosis should be confirmed by ultrasound-guided fine-needle aspiration (3–4 Fr) with bacteriological and cytological work-up ( 5.8 d–f). If it is an abscess, the diagnostic procedure can be expanded to definitive treatment in terms of quantitative evacuation; an abscess less than 8–10 cm across may be aspirated repeatedly, while catheter drainage is recommended for abscess with

Sonographic findings. Ultrasound can visualize the following alterations indicative of splenic trauma:

●Hematoperitoneum: free intraperitoneal, perisplenic, perihepatic fluid and/or fluid in the rectovesical pouch or rectouterine pouch in primary splenic rupture with hemorrhage into the peritoneal cavity.

●Subcapsular splenic rupture: liquid zones (anechoic, isoechoic, or hyperechoic) between the parenchyma and capsula of the spleen.

●Organ injury: destruction of the parenchymal texture, with visualization of textural nonhomogeneity or splenic laceration of varying severity as direct indication of tissue lesions and/or hemorrhage.

Subcapsular splenic rupture. External trauma leading to subcapsular splenic rupture ( 5.9a–f) frequently results in the hemorrhage between parenchyma and capsula capping the organ, primarily along the convex diaphragmatic surface; this can produce a double contour on ultrasound examination. Subcapsular hemorrhage around the splenic hilum is less common.

As in the post-traumatic subcapsular hemorrhage of the liver, it has to be pointed out that the acute subcapsular splenic hemorrhage may also be distinctly hyperechoic and could easily be overlooked on cursory examination. Sometimes an enlarged left hepatic lobe may mimic a subcapsular mass.

Splenic Metastasis

Splenic metastasis is detected in approximately 7% of autopsies. Metastasis in the spleen is far less common than in the liver, the hypothesis being that the spleen is equipped with a special immunological microenvironment.

Ultrasound appearance. Classification of splenic metastasis is along the same lines as in the liver, the splenic parenchyma being the in-vivo reference. The metastases can be classified as being anechoic, hypoechoic, isoechoic, hyperechoic, and complex. The most common sonographic types demonstrated in the spleen are hypoechoic metastases. Larger metastases may exhibit central colliquation.

All metastases may present with or without a halo, which can be regarded as typical of, but not specific to, hepatic and splenic malignancy (splenic metastases can be isoechoic or even hyperechoic in comparison to splenic tissue

and are discussed here for systematic reasons ( 5.10a–f).

Metastasis in direct extension. Splenic metastasis may also arise by direct extension of pancreatic, colonic, and gastric cancer ( 5.11). In rare cases, malignancies of the lung or diaphragm may break through and invade the spleen in continuity. Also peritoneal metastasis may encase and invade the spleen.

Complications. Complications may be localized perforation, abscess, splenic hemorrhage, and rupture (5.10e–i). Calcification of splenic metastasis has also been reported as well as tumor-induced splenic vein thrombosis.

Hypoechoic Hypervascularized Mass

Round masses are sometimes detected as incidental findings in color Doppler ultrasound ( 5.12 g–i) and show an increased vascularization in CEUS ( 5.12j–m). These hypervasculated tumors show no growth according to present observations and most likely correspond to vascular tumors, such as hemangioma. A follow-up exam by ultrasound is necessary.7