Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

SPLEEN

splenic hamartomas and in splenic parenchyma (21). Splenic peliosis can result in spontaneous splenic rupture, probably due to minor trauma.

The imaging appearance of splenic peliosis is similar to that seen in the liver. Computed tomography reveals hypodense tumors.

Hamartoma

The rare splenic hamartoma, or splenoma, is believed to be congenital in origin. Two types occur: white pulp, composed of aberrant lymphoid tissue, and red pulp, composed mostly of sinuses. Often a mix of both is found. A histopathologic differentiation from lymphoma is possible with most of these tumors. Most are detected incidentally. An occasional one is associated with thrombocytopenia or pancytopenia.

The CT appearance is similar to that seen with hamartomas in other locations. They range from homogeneous to heterogeneous. Most do not contain calcifications. Some have a cystic component. They tend to be isodense to splenic tissue. Some exhibit prolonged contrast enhancement. US reveals a well-marginated and somewhat hypoechoic tumor, at times containing multiple punctate foci, probably representing necrosis.

Most hamartomas are isointense on T1and hyperintense on T2-weighted images. They have heterogeneous early postcontrast enhancement, often enhancing more uniformly on delayed images. Some hamartomas, however, have an enhancement pattern similar to hemangiomas. Prolonged enhancement on postcontrast CT and MR images differentiates these lesions from most malignancies.Aside from necrotic regions, angiography reveals them to be hypervascular.

Most hamartoma have similar uptake of Tc-99m-HSA to hemangiomas. Radiocolloid uptake is less within the tumor than in a normal spleen.

Cysts

Pathologically, most splenic cysts can be divided into epithelial-lined cysts, which are developmental in origin, and nonepithelial cysts, which are mostly sequelae of a prior hematoma. Radiologists often refer to both types as simple cysts, which is a descriptive term. Except for echinococcal cysts, infections rarely result in a splenic cyst.

A simple cyst, either developmental or posttraumatic, has a well-defined wall, consists of fluid density, and does not enhance postcontrast. Some cysts contain septa. Hemorrhage into a simple cyst or the presence of cholesterol crystals result in hyperechoic fluid. Calcifications eventually develop in some cyst walls.

A large splenic cyst is one of the causes of splenomegaly.

Simple cysts have been treated by laparoscopic spleen-preserving surgery.

Epithelial Cysts

Most developmental cysts, also called epidermoid cysts, mesothelial cysts, primary cysts, and true cysts, probably represent sequelae of mesothelial cell remnants trapped in splenic tissue. Several familial splenic cysts are reported. Some authors classify hemangiomas and cystic lymphangiomas as true cysts.

These cysts tend to be asymptomatic until trauma, at times minor, leads to hemorrhage and an increase in cyst size and then rupture. At times infection or compression of adjacent structures reveals its presence. Most are unilocular.

Prenatal US identified a splenic cyst at 31 weeks’ gestation (22); the cyst had spontaneously regressed when the infant was 7 months of age.

Nonepithelial Cysts

The majority of cysts encountered in the West are posttraumatic; these do not have an epithelial lining and are also called pseudocysts, hemorrhagic cysts, and serosal cysts. At times prior hematoma-inducing trauma was relatively minor and is not remembered. Eventually a hematoma evolves into a nonepithelial cyst containing serous fluid.

Pancreatic Pseudocyst

Some cysts originating in an adjacent structure involve the spleen to the extent that imaging will suggest a splenic origin. For example, a pancreatic pseudocyst (also called a false cyst) arising from the tail of the pancreas can extend into the spleen and appear intrasplenic. Also in the dif-

ferential is an abscess and a cystic or necrotic neoplasm.

These cysts can be drained percutaneously.

Lymphangioma

Splenic lymphangiomatosis consists of multiple endothelial-lined cysts; it is a rare tumor. Some are associated with splenomegaly or hypersplenism. Most are discovered incidentally. Not uncommonly, liver and other site lymphangiomas are also identified.

Imaging typically shows a multilocular cyst or multiple thin-walled cysts, most often subcapsular in location. An occasional one contains curvilinear calcifications. They are hypodense and do not enhance with postcontrast CT. Occasionally diffuse lymphangiomatosis appears on postcontrast CT as a mottled spleen. They are hyperintense on T2-weighted images, except that cyst septa, consisting of fibrous connective tissue, appear hypointense.

Hydatid disease is in the differential diagnosis of a cystic lymphangioma.

Whether these patients should be treated (resection or embolization) or whether observation is appropriate depends on symptomatology.

Neoplasms

Angioma/Angiosarcoma

An angioma is an unusual splenic tumor that is difficult to classify. This rare, benign vascular tumor is composed of anastomosing vascular channels containing papillary projections. Littoral cell angiomas are rare neoplasms originating from cell lining sinuses (littoral cells) rather than larger vessels and have characteristic immunohistochemical properties. For unknown reason, anemia or thrombocytopenia develops in some patients. These tumors range from a focal tumor, to a miliary pattern, to ones replacing most of the spleen. Most are benign, although a littoral cell angiosarcoma also occurs. Littoral cell angiomas are hypodense relative to normal spleen tissue (23); dynamic CT reveals progressive and homogeneous contrast enhancement to the point that they resemble normal splenic parenchyma.

ADVANCED IMAGING OF THE ABDOMEN

A primary angiosarcoma is a rare but highly malignant splenic neoplasm. It can involve accessory spleens. Splenomegaly is not uncommon and spontaneous splenic rupture does occur with angiosarcomas. Imaging of some of these tumors suggests abscesses.

Only a few MR findings of primary splenic angiosarcomas are reported. One was hypointense both on T1and T2-weighted images, which differentiates it from most hemangiomas (24); intratumoral hemorrhage and necrosis were evident. Postgadolinium imaging revealed heterogeneous enhancement.

Lymphoma

The most common focal splenic tumor is malignant lymphoma. Most primary splenic lymphomas appear as a large, solitary tumor; multifocal tumors are less common. These tumors tend to enhance less than splenic parenchyma on postcontrast CT. Only an occasional one shows rim enhancement (Fig. 15.9). The majority of primary lymphomas are hypoechoic on US.

Splenomegaly is common but not universal with splenic involvement by lymphoma. Conversely, splenomegaly may be due to some other underlying disorder. Calcifications are unusual, but have developed in both untreated and, more often, treated lymphoma. Large necrotic nodules mimic an abscess (Fig. 15.10).

Aside from splenomegaly, splenic involvement by systemic lymphoma tends to be missed by imaging. In particular, diffuse lymphomatous infiltration is difficult to detect. To put splenic involvement by systemic lymphoma in perspective, among 680 patients with malignant lymphoma, US revealed abnormal splenic texture in only 15% (25); among these, about one third each were Hodgkin’s disease, lowgrade non-Hodgkin’s lymphoma, and highgrade non-Hodgkin’s lymphoma.

The US appearance of lymphoma involving the spleen varies considerably (25): diffuse involvement in 37%, small nodular in 39%, large nodular in 23%, and bulky in 2%. High-grade non-Hodgkin’s lymphomas were either large nodular or small nodular, while low-grade nonHodgkin’s lymphomas and Hodgkin’s disease were either diffuse or had a small nodular pattern.

Contrast-enhanced MR reveals diffuse splenic infiltration to have immediate heterogeneous enhancement, becoming isointense on delayed views. Focal lymphoma is hypointense on immediate postcontrast images.

Leukemia

Diffuse leukemic infiltration of the spleen results in a homogeneously enhancing enlarged spleen. Associated lymphadenopathy is common.

Laparoscopic splenectomy is feasible in patients with leukemia and Hodgkin’s lymphoma.

Plasmacytoma/Multiple Myeloma

The rare primary splenic plasmacytoma most often presents with splenomegaly. Some of these patients develop disease progression after splenectomy but in an atypical fashion for multiple myelomas.

Metastases

An isolated metastasis to the spleen is not common. Presumably most abnormal cells are destroyed in the spleen. Colon, lung, ovarian, and other cancers result in multiple metastases, generally late in the course and most metastases

are small. At times a necrotic metastasis mimics a cyst. Only an occasional melanoma is encountered.

Calcifications develop in an occasional slowgrowing tumor. Most metastases are hypodense on CT and are isointense on precontrast MR images; the exception is a melanoma, which often has a heterogeneous appearance. Metastases appear hypointense on immediate postcontrast MR images, becoming isointense on delayed images.

Diffuse splenic metastases can be missed by CT. Thus a diffuse metastatic seminoma was not detected by CT but was evident on FDG-PET (26).

Other Neoplasms

ADVANCED IMAGING OF THE ABDOMEN

Table 15.2. Conditions associated with splenic calcifications

Posttraumatic cyst

Infection/inflammation

Tuberculosis

Histoplasmosis

Brucellosis

Hydatid cyst

Healed abscess

Atherosclerosis

Hemangioma

Neoplasm

Infarcts

Sickle cell disease

Silicosis

Thorotrast

The rare cystadenocarcinoma probably arises from embryonic rests or mesothelium.

Splenic leiomyosarcomas are very rare.

Calcifications

Some of the conditions associated with splenic calcifications (Fig. 15.11) are listed in Table 15.2.

Hepatosplenic silicosis leads to calcifications in both the liver and spleen, and occasionally

Figure 15.11. Extensive splenic calcifications detected by CT (arrow). Either tuberculosis or histoplasmosis can produce these changes. (Courtesy of Algidas Basevicius, M.D., Kaunas Medical University, Kaunas, Lithuania.)

even eggshell-like calcified lymph nodes. Conventional radiographs reveal numerous calcified nodules, which are better identified by CT. Biopsy reveals birefringent particles within the nodules.

Vascular Disorders

Portal Hypertension

Idiopathic portal hypertension, or Banti’s disease, consists of anemia, splenomegaly, and portal hypertension. It is a distinct entity differing from liver cirrhosis-associated portal hypertension in both its histopathology and portal hemodynamics.

Splenomegaly is common in portal hypertension. Regardless of etiology, the interrelationship between portal hemodynamics and splenomegaly is complex and poorly understood. A rare cause of portal hypertension but entailing a normal-size spleen is a splenic arteriovenous fistula; contrast-enhanced imaging or Doppler US should be diagnostic of a fistula.

Duplex Doppler US appears useful in differentiating between congestive splenomegaly as seen in patients with liver cirrhosis and splenomegaly due to various myeloand lym-

SPLEEN

phoproliferative disorders; the maximum portal flow velocity in patients with proliferative disordersis normal, but is reduced in those with congestive splenomegaly.

Leukopenia and thrombocytopenia develop in patients with cirrhosis, portal hypertension, and hypersplenism. In this clinical setting, patients with a superimposed hepatocellular carcinoma undergoing transcatheter hepatic arterial embolization also underwent partial splenic embolization and infarction (27); the leukopenia and thrombocytopenia were corrected in a majority of patients if more than 50% of their spleens were infarcted.

Infarction

Vascular emboli result in focal splenic infarction, at times multiple. Splenic artery thrombosis is associated with total splenic infarction. Rarely, a splenic infarct occurs in a setting of congestive splenomegaly or pancreatitis, at times together with splenic vein thrombosis and possibly other infarctions. The risk of infarction is increased in a setting of portal hypertension. Rarer causes of splenic infarction include systemic mast cell disease (28) and celiac disease (29); the latter is also associated with splenic venous thrombosis.

Occasionally intrasplenic gas bubbles are detected after a major infarct; they develop even without an infection.

An infarct is a common cause of a focal splenic tumor. A typical infarct is wedge-shaped and located adjacent to the splenic capsule. Less often an infarct has a round or nodular outline. Computed tomography reveals lack of contrast enhancement. Occasionally a neoplasm has a similar appearance. The rare total splenic infarction shows only peripheral contrast enhancement, presumably secondary to a capsular artery supply. Nevertheless, the lack of splenic contrast enhancement is not pathognomonic of a total infarction; a more common cause is severe hypotension.

Initially after an infarct, US reveals a hypoechoic tumor. Later, scarring results in a gradual hyperechoic appearance. Similar to CT, infarcts are identified on delayed postcontrast MRI as hypointense wedge-shaped regions adjacent to the capsule.

Immunosuppression

Abnormal CT scans in HIV patients should not be routinely ascribed to AIDS; a second disease, consisting of either superimposed infection or a neoplasm is most often responsible for abnormal findings.

Hepatosplenic abscesses are not uncommon in AIDS patients, often being secondary to unusual organisms. Most are small and multiple. An US “snowstorm” appearance is found with some opportunistic liver and spleen infections, reflecting fibrosis or a fibrinous exudate. Abdominal US with a 3.5-MHz transducer will miss small abscesses in these patients; a 5-MHz transducer should identify more abscesses.

Similar to other patients, splenic tuberculous abscesses in immunocompetent patients are hypodense on CT and hypoechoic on US.

Examination and Surgical

Complications

Splenectomy

Compared to an open splenectomy, in both adults and children a laparoscopic splenectomy requires a longer operative time but the patient’s overall hospital stay is shorter. Most laparoscopic splenectomies are performed for a normal-sized or moderately enlarged spleen, although a laparoscopic approach is feasible in a patient with marked splenomegaly. Some surgeons believe that if the spleen is enlarged, preoperative splenic artery embolization makes laparoscopic splenectomy easier (30).

Following splenectomy, residual splenic tissue can be identified with In-111–labeled autologous platelet SPECT.

An increased risk for postsplenectomy infection is well known. Splenectomy results in depressed phagocytosis and a decrease in serum levels of immunoglobulin M (IgM). The consequences of splenectomy are not trivial, especially in children and in those undergoing splenectomy as part of lymphoma therapy. This risk tends to lessen after several years.

A subphrenic abscess is a recognized complication after splenectomy, developing either shortly after surgery or, less commonly, on a

delayed basis. Computed tomography should detect a subphrenic abscess, but keep in mind that an occasional abscess mimics an intact spleen. Image-guided drainage is generally the treatment of choice, with surgery reserved for multiseptated abscesses or if percutaneous drainage fails.

Thorotrast

Thorotrast deposits can be visualized in the spleen with conventional radiography and CT. The spleen tends to be atrophic.

A Thorotrast-induced angiosarcoma is rare in the spleen, with most occurring in the liver. The effect of prior Thorotrast use is discussed further in Chapter 7.

References

1.Lieberman S, Libson E, Maly B, Lebensart P, Ben-Yehuda D, Bloom AI. Imaging-guided percutaneous splenic biopsy using a 20or 22-gauge cutting-edge core biopsy needle for the diagnosis of malignant lymphoma. AJR 2003;181:1025–1027.

2.Deux JF, Salomon L, Barrier A, Callard P, Bazot M. Acute torsion of wandering spleen: MRI findings. AJR 2004;182:1607–1608.

3.Lorberboym M, Vallabhajosula S, Lipszyc H, Pastores G. Scintigraphic evaluation of Tc-99m-low-density lipoprotein (LDL) distribution in patients with Gaucher disease. Clin Genet 1997;52:7–11.

4.Kimura F, Ito H, Shimizu H, et al. Partial splenic embolization for the treatment of hereditary spherocytosis. AJR 2003;181:1021–1024.

5.Shanmuganathan K, Mirvis SE, Boyd-Kranis R, Takada T, Scalea TM. Nonsurgical management of blunt splenic injury: use of CT criteria to select patients for splenic arteriography and potential endovascular therapy. Radiology 2000;217:75–82.

6.Moore EE, Cogbill TH, Jurkovich GJ, Shackford SR, Malangoni MA, Champion HR. Organ injury scaling: spleen and liver (1994 revision). J Trauma 1995;38: 323–324.

7.Sivit CJ, Frazier AA, Eichelberger MR. Prevalence and distribution of extraperitoneal hemorrhage associated with splenic injury in infants and children. AJR 1999;172:1015–1017.

8.Kimpel M, Zander T, Dux M. [Spontaneous occult splenic rupture after Salmonella enteritidis infection.] [German] Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 2001;173:380–381.

9.Resende V, Petroianu A. Subtotal splenectomy for treatment of severe splenic injuries. J Trauma 1998;44: 933–935.

ADVANCED IMAGING OF THE ABDOMEN

10.Emery KH, Babcock DS, Borgman AS, Garcia VF. Splenic injury diagnosed with CT: US follow-up and healing rate in children and adolescents. Radiology 1999;212: 515–518.

11.Bittar I, Cohen Solal JL, Cabanis P. [Volvulus of the mobile spleen. Conservative laparoscopic treatment.] [French] Presse Med 2001;30:1005–1006.

12.Hierholzer J, Fuchs H, Menzel B. [Intrahepatic splenosis.] [German] Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr 2001;173:769–771.

13.Rickert CH, Maasjosthusmann U, Probst-Cousin S, August C, Gullotta F. A unique case of cerebral spleen. Am J Surg Pathol 1998;22:894–896.

14.Warshauer DM, Molina PL, Worawattanakul S. The spotted spleen: CT and clinical correlation in a tertiary care center. J Comput Assist Tomogr 1998;22:694– 702.

15.Tohme A, Hammoud A, el Rassi B, Germanos-Haddad M, Ghayad E. [Human brucellosis. Retrospective studies of 63 cases in Lebanon.] [French] Presse Med 2001; 30:1339–1343.

16.Harned RK 2nd, Thompson HR, Kumpe DA, Narkewicz MR, Sokol RJ. Partial splenic embolization in five children with hypersplenism: effects of reduced-volume embolization on efficacy and morbidity. Radiology 1998;209:803–806.

17.Monzawa S, Tsukamoto T, Omata K, Hosoda K, Araki T, Sugimura K. A case with primary amyloidosis of the liver and spleen: radiologic findings. Eur J Radiol 2002;41:237–241.

18.Thanos L, Zormpala A, Brountzos E, Nikita A, Kelekis D. Nodular hepatic and splenic sarcoidosis in a patient with normal chest radiograph. Eur J Radiol 2002;41:10–11.

19.Zilkha A, Madan V, Leonidas JC, Valderrama E. Liver and spleen MRI findings in virus-associated hemophagocytic syndrome in a patient with acute lymphocytic leukemia. Pediatr Radiol 1998;28:920– 922.

20.Schulz AS, Urban J, Gessler P, Behnisch W, Kohne E, Heymer B. Anaemia, thrombocytopenia and coagulopathy due to occult diffuse infantile haemangiomatosis of spleen and pancreas. Eur J Pediatr 1999;158: 379–383.

21.Lam KY, Yip KH, Peh WC. Splenic vascular lesions: unusual features and a review of the literature. [Review] Aust N Z J Surg 1999;69:422–425.

22.Yilmazer YC, Erden A. Complete regression of a congenital splenic cyst. J Clin Ultrasound 1998;26:223– 224.

23.Levy AD, Abbott RM, Abbondanzo SL. Littoral cell angioma of the spleen: CT features with clinicopathologic comparison. Radiology 2004;230:485–490.

24.Imaoka I, Sugimura K, Furukawa M, Kuroda S, Yasui K. Computed tomography and MR findings of splenic angiosarcoma. Radiat Med 1999;17:67–70.

25.Gorg C, Weide R, Schwerk WB. Malignant splenic lymphoma: sonographic patterns, diagnosis and follow-up. Clin Radiol 1997;52:535–540.

26.Lenzo NP, Moschilla G, Patrikeos A. Diffuse splenic metastases from seminoma visualized on FDG PET. AJR 2004;183:525–527.

27.Han MJ, Zhao HG, Ren K, Zhao DC, Xu K, Zhang XT. Partial splenic embolization for hypersplenism