Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

ing a pelvic tumor. CT and MR reveal an absent spleen in its usual location and a splenic-sized tumor inferiorly. Contrast enhancement detects a vascular pedicle. A wandering spleen can be diagnosed with sequential liver-spleen scintigraphy and with In-111-leukocyte scintigraphy. An occasional such wandering spleen is associated with dilated feeding vessels within lax ligaments. Lax suspensory ligaments predispose a wandering spleen to splenic torsion and has even caused splenic flexure volvulus. Splenic torsion is a rare cause of an acute abdomen; at times contrast enhanced imaging reveals a partly nonenhancing spleen due to ischemia (2).

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common. These conditions are part of the heterotaxy syndrome (discussed in Chapter 14).

Splenogonadal Fusion

Splenogonadal fusion in males is discussed in Chapter 13. This rare congenital anomaly is associated with orofacial and extremity abnormalities. Imaging detects a tumor in the lower abdomen, with radiocolloid spleen scintigraphy and single photon emission computed tomography (SPECT) showing uptake similar to splenic tissue.

Accessory Spleen

The term accessory spleen is used to designate additional separate splenic tissue believed to be congenital in origin. It is a common condition, with most accessory spleens located near the splenic hilum, some even being intrapancreatic in location where they can mimic a pancreatic tumor. Although most are relatively fixed in position, an occasional one fits the criteria of a wandering spleen, such as an intrascrotal paratesticular accessory spleen. Similar to a main spleen, cysts can also develop in an accessory spleen. In a setting of splenomegaly an accessory spleen will also enlarge. Thus an accessory spleen enlarges secondary to portal hypertension. Torsion of an accessory spleen vascular pedicle can result in vascular compromise and progress to ischemia and infarction.

An accessory spleen is detected by computed tomography (CT), ultrasonography (US), MRI, and scintigraphy. On noncontrast CT it mimics enlarged lymph nodes, but after contrast it enhances similar to the spleen. Color Doppler US also suggests the diagnosis. Accessory spleens have the same MR signal intensity as normal spleen parenchyma on all sequences.

A Tc-99m–sulfur colloid scan shows uptake similar to the spleen. Occasionally such uptake results in confusion. Thus after a splenectomy somatostatin receptor scintigraphy reveals uptake in an accessory spleen.

Asplenia and Polysplenia

The terms asplenia and polysplenia are descriptive only, and associated abnormalities are

Gaucher’s Disease

Gaucher’s disease is an autosomal-recessive storage disorder caused by a defect in the lysosomal enzyme b-glucosidase, an enzyme needed to degrade sphingolipids. About 40 mutations of the b-glucosidase gene have been identified, with clinical disease variability depending on the specific type of gene mutation involved. Its hallmark is pathologic storage of glycolipid in mononuclear phagocytes, with a tissue reaction to these lipid-engorged macrophages, or Gaucher cells, probably leading to further organ damage. The diagnosis is made by showing decreased acid b-glucosidase activity in peripheral blood leukocytes. A histologic diagnosis is not necessary in most patients. Genotyping is available and does detect most carriers, but the variable phenotypic expressivity limits the use of genotyping as a practical tool.

Gaucher’s disease is subdivided into three types based on the presence or absence of neurologic involvement: type 1, nonneuronopathic; type 2, severe neuronopathic; and type 3, a chronic, less severe neuronopathic form similar to type 1, but with more severe, systemic manifestations.A rare neonatal form leads to hydrops fetalis.

The disease involves multiple organs but varies considerably in its clinical expressivity and severity. Typically, splenomegaly, bone lesions, and eventually central neurologic involvement become evident. These patients are at increased risk of developing lymphoproliferative disorders, including non-Hodgkin’s lymphoma.

SPLEEN

Moderate-to-severe splenomegaly due to reticuloendothelial hypertrophy and hyperplasia is a common and often the only imaging finding. Hepatomegaly generally is not a prominent feature. A number of CT and US techniques have been developed to measure splenic volume. These are useful in patients with Gaucher’s disease who often undergo serial follow-up studies. Follow-up of splenic volume changes are best obtained using the same imaging modality.

A minority of patients have well-defined homogeneous hypodense nodules scattered throughout the spleen. Ultrasonography shows variable echogenicity in these nodules.An irregular, inhomogeneous appearance is seen if these nodules become confluent. Of interest is that splenectomized patients tend to develop retroperitoneal or periportal lymphadenopathy. Magnetic resonance imaging also identifies splenic nodules in some of these patients, with these nodules being isointense on T1and hypointense on T2-weighted images. Also, MR detects splenic infarcts in these patients.

These patients have decreased plasma levels of low-density lipoproteins. Technetium-99m– low-density lipoprotein scintigraphy shows that these proteins are taken up by the spleen, bone marrow, and liver reticuloendothelial system

(3). Such serial studies appear of value in follow-up after therapy.

Splenectomy and heterotopic splenic autotransplantation have been used to treat hypersplenism. Partial splenectomy often leads to enlargement of the splenic remnant. It is not clear if such enlargement is due to splenic tissue regeneration or continued glycolipid deposition or both.

An occasional patient with massive splenomegaly develops a splenic abscess.

Thalassemia

Hypersplenism can be corrected in children with thalassemia by partial or total surgical splenectomy. An alternative is partial splenic embolization. After embolization the spleen decreases in size and fewer transfusions are necessary.

Hereditary Spherocytosis

Patients with hereditary spherocytosis have hemolysis, either compensated or leading to anemia, and are at increased risk for bilirubinate gallstones, erythroid aplasia, and hemolytic crises.

Therapy consists of splenectomy, although partial splenic embolization is an option (4).

Niemann-Pick Disease

Niemann-Pick type C disease is an autosomalrecessive lipid storage disorder, leading to an accumulation of syringomyelin and cholesterol in the brain, liver, and spleen. Most affected patients develop neurologic symptoms. Isolated nodular splenomegaly develops in this condition.

Sickle Cell Disease

Patients with sickle cell disease are at risk for splenic infection, abscess, acute splenic sequestration crisis, hypersplenism, and splenic infarction. Most acute infarctions involve only a portion of the spleen, although total splenic infarction does develop. During an acute sequestration crisis the hematocrit drops and spleen enlarges, at times massively. Computed tomography identifies multiple hypodense foci in the spleen. Multiple episodes of focal splenic infarction eventually result in a small spleen, at times containing calcifications.

In patients homozygous for this condition MRI reveals a signal void on T2-weighted sequences due to a combination of iron deposition and superimposed calcifications (iron overload is discussed in Chapter 7). These patients have impairment of splenic reticuloendothelial function; scintigraphy with Tc- 99m–sulfur colloid reveals nonvisualization of the spleen.

Patients with sickle cell disease develop round intrasplenic nodules, shown to represent functioning splenic tissue; this tissue is hypodense on CT, hypoechoic on US, appears as normal spleen on MRI, and manifests uptake of Tc-99m–sulfur colloid. Imaging thus allows distinguishing these nodules from abscesses and infarcts.

Trauma

In the United States, the initial triage of trauma patients classifies them into those who are unstable and require immediate surgery or stable; the latter patients generally undergo contrast-enhanced CT, with a decision for surgery, angiographic therapy, or conservative management based on CT findings. Quite often splenic trauma is only one element of multisystem trauma, and the decision for a specific therapy is modified accordingly. Intravenous contrast is necessary for adequate CT evaluation. Using splenic arteriography as a gold standard, in 78 hemodynamically stable patients CT achieved an 81% sensitivity and 84% specificity in predicting the need for splenic therapy (5). In general, US is believed to be not as sensitive in detecting the extent of injury.

A number of injury severity schemes based on contrast-enhanced CT have been developed. Some use the degree of splenic laceration and devascularization as a classification guide. Both in adults and children these schemes have had limited success in guiding therapy. A splenic injury classification scale, devised by the American Association for the Surgery of Trauma, is outlined in Table 15.1. In general, the injury severity score best correlates with outcome.

Some patients managed conservatively develop delayed complications, including

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splenic or subphrenic abscess, bleeding from a (pseudo)aneurysm, or splenic rupture. Whether routine follow-up CT is warranted in these patients is controversial. Follow-up CT in otherwise asymptomatic patients does not appear to be routinely warranted. Whether US follow-up, including color Doppler, is warranted is not clear.

Blunt abdominal trauma can result in pseudoaneurysms and a splenic arteriovenous fistula; some of these fistulas resolve spontaneously.

Hematoma

A hematoma can be subcapsular or intraparenchymal in location or, with rupture of the capsule, even perisplenic.

With noncontrast CT, intrasplenic hematomas range from hypodense to hyperdense (density-time variations are discussed in Chapter 14). Contrast-enhanced CT reveals a hematoma as a nonperfused region surrounded by contrast-enhancing normal parenchyma. A subcapsular hematoma tends to have a crescent shape, while perisplenic ones are more irregular. Multiple episodes of spontaneous splenic bleeding can eventually result in a CT “onion skin” appearance.

A recent hematoma has a complex US appearance, and clotted blood in a hematoma can be

SPLEEN

isoechoic to splenic tissue. Thus a perisplenic hematoma may simply blend into the spleen until it liquifies later on. In time, a hematoma gradually becomes anechoic.

Most hematomas eventually resolve; an occasional one becomes infected and requires drainage. Some evolve into nonepithelial cysts. Splenic hematomas can be drained percutaneously, although some recur. Gallium-67 subtraction scintigraphy is useful if an infected splenic hematoma is suspected.

Laceration/Rupture

Splenic laceration is usually associated with intraperitoneal hemorrhage; occasionally splenic injury also leads to extraperitoneal hemorrhage into the anterior pararenal space (7).

Although uncommon, delayed splenic rupture does occur after trauma. Occasionally even a minor splenic laceration leads to hemorrhage days later, at times massively. This topic is difficult to place in proper perspective because splenic rupture has been reported even years after prior injury.

Splenic rupture after minor trauma should lead to a search for underlying disease. In Western countries the leading cause of spontaneous splenic rupture is infectious mononucleosis. Rupture is a recognized complication in patients with malaria. Rarely, spontaneous splenic rupture occurs in patients with HIV/AIDS, acute leukemia, sickle cell disease, amyloidosis, hepatitis virus infection, and even Salmonella enteritidis infection (8). Splenomegaly due to such entities as Wilson’s disease predisposes to rupture. Rupture of a splenic cyst after minor trauma can result in an acute abdomen. Splenic rupture is a complication of various interventional procedures, such as colonoscopy, extracorporeal shock-wave lithotripsy, and even after insertion of an implantable defibrillator using a left subcostal approach.

Precontrast CT of a laceration is seen as an irregular, hypodense defect (Fig. 15.1). Post–intravenous contrast, a laceration is better defined by surrounding contrast-enhancing normal splenic parenchyma; an adjacent subcapsular or extrasplenic hematoma is often present. With active arterial bleeding at the time of study, contrast CT can identify extravasation.

Figure 15.1. Splenic laceration. Ascites is also present.

Avulsion

Most splenic avulsions are secondary to major trauma. Avulsion has occurred, however, secondary to colonoscopy and even in a patient with hyperemesis.

Therapy

The overall trend is to manage conservatively hemodynamically stable patients with splenic injury, generally detected by CT, and with no other indication for laparotomy. Conservative management tends to be unsuccessful if a traumatic pseudoaneurysm or frank extravasation is detected on an initial CT examination; these patients should be treated with early surgical or endovascular therapy. Some of these patients undergo splenic arteriography and, if contrast extravasation is detected, splenic artery embolization is performed. Transcatheter arterial embolization therapy performed in trauma patients with angiographically evident contrast extravasation, arterial disruption, or major arteriovenous fistula is successful in over 90% of these patients.

Computed tomography identifies a splenic artery pseudoaneurysms as contrast blush; arteriography confirms this finding, and a majority of these aneurysms can be successfully embolized.

A subtotal splenectomy, with preservation of the upper splenic pole supplied by splenogastric

vessels, was performed in patients with severe splenic injuries (9). Partial laparoscopic splenectomy following splenic trauma is also feasible.

A preexisting diseased (enlarged) spleen is more prone to laceration/rupture than a normal spleen and patients with such a spleen probably undergo a higher rate of splenectomy than those with a normal-size spleen. Conservative management, however, can be successful in stable patients with trauma to a diseased spleen.

At times heterotopic splenic autotransplantation is performed after abdominal trauma requiring total splenectomy. Whether the autotransplanted splenic tissue is functioning can be evaluated with red blood cell scintigraphy.

Follow-up US in children with blunt splenic trauma found that the time to healing is related to injury severity (10); sequelae include an occasional splenic cyst.

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Figure 15.2. Splenosis.The patient had a splenectomy as a child due to trauma. Computed tomography (CT) reveals left upper quadrant soft tissue nodules. Serial studies showed no change. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

Torsion/Volvulus

Occasionally a wandering spleen twists on its axis on either an acute or chronic basis, a condition occurring in both children and adults. Torsion can be suggested in the appropriate clinical setting if the spleen is not in its usual right upper quadrant location (the condition is really a volvulus, although the term torsion is often used interchangeably in the literature).

When acute, the sudden onset of abdominal pain suggests an acute abdomen. On a more chronic basis, few symptoms are elicited and the condition is often detected incidentally when an abnormal lower abdominal or even pelvic tumor is detected and the splenic fossa empty.

Imaging suggests the diagnosis. Computed tomography reveals a hypodense spleen, at times still showing postcontrast peripheral enhancement. Ultrasonography detects a hypoechoic solid spleen, and Doppler US reveals absent blood flow, confirming the diagnosis.

Torsion and infarction also develop in an accessory spleen, especially if it has a long vascular pedicle. A number of these rare events occur in children.

Laparoscopic splenopexy of a mobile spleen has been performed (11).

Splenosis

Acquired splenic tissue outside the spleen, such as ectopic implantation from prior trauma, is termed splenosis, thus distinguishing it from an accessory spleen, which is a congenital condition. Splenosis tends to present with multiple nodules; accessory spleens, on the other hand, are few in number. Splenosis involves the peritoneum, retroperitoneal tissues, thoracic cavity, and even subcutaneous abdominal wall tissues (Fig. 15.2). It can develop years after splenectomy. Even intrahepatic splenosis has been reported (12). One patient developed cerebral splenosis 15 years after splenectomy (13).

Splenosis can become quite large, even mimicking an adjacent neoplasm. Most of these splenic nodules have a smooth outline. If sufficiently large, splenosis is imaged by CT, US, MRI, and scintigraphy. Ultrasonography reveals homogeneous echogenicity.

Splenosis should be differentiated from polysplenia.

Splenomegaly

The definition of an abnormally enlarged spleen (splenomegaly) is arbitrary. One definition used by ultrasonographers is a spleen that deviates by