Dual radiopharmaceutical imaging in congenital asplenia syndrome

Howell-Jolly bodies and liver-spleen scanning for assessment of splenic filtrative function yields discordant results in renal transplant recipients

Given discrepancies between methods for diagnosing hyposplenism, the purpose of this study was to evaluate the effect of the spleen size on the correlation between the methods, and to propose a model for improving the interpretation. Patients with renal allografts were included, in whom the spleen was assessed using Doppler ultrasound, scintiscan, and the presence of Howell-Jolly bodies (HJBs) in peripheral smears. In 35 subjects, scintiscan and HJBs were normal (Group 0); 20 had an abnormal result in both methods (Group 1); 34 had discordant results with HJBs present (Group 2); and 14 had discordant results with decreased spleen uptake (Group 3). There was no association between HJBs and scintiscan. The patients of Groups 1 and 2 had smaller spleens. The patients with smaller spleen had more hematological evidence of hyposplenism and exhibit smaller discrepancies between the methods than patients with larger spleen. The spleen can tip the balance from a normal to impaired function provided that the spleen size is below the critical mass required to maintain splenic function. A mild impairment of phagocytic function and slight dyserythropoiesis along with a small spleen would result in decreased take up of radiocolloid or the appearance of HJBs in blood smears.

Asplenia and Polysplenia

Abdominal sonograms on seven patients with asplenia syndrome and six patients with polysplenia syndrome were retrospectively reviewed. All seven patients with asplenia had a horizontal symmetric configuration of the liver, and three patients had the cardiac apex opposite the stomach. Four of six patients with polysplenia syndrome had a symmetric configuration of the liver, and in five patients the cardiac apex was opposite the stomach. In two of six patients with polysplenia syndrome, multiple spleens were observed sonographically, and the spleen was noted sonographically to be lobulated in three of the patients. The spleen was not visible on at least one sonographic examination in three patients with polysplenia in which the presence of the spleen was subsequently documented. Four patients with polysplenia syndrome showed an interruption of the inferior vena cava. The authors conclude that the knowledgeable sonographer can usually identify the complex abdominal anomalies that are observed in these syndromes if an organized survey of the abdominal organs, particularly the venous structures, is performed. The spleen may be difficult to identify in some patients, and other abdominal anomalies, especially interruption of the interior vena cava can serve as valuable clues that the spleen is probably present, and further search for it is indicated.

Splenic function: physiology and splenic hypofunction

A wide variety of disorders can result in diminished splenic function. The pathophysiology appears to be clearly defined in some instances, such as congenital asplenia and disorders of splenic vascular obstruction or congestion. In others, such as the autoimmune and GI disorders, the mechanism remains poorly defined. Further research is needed. The hyposplenia which occurs in many of these disorders has been associated with an increased risk of life-threatening, overwhelming bacterial sepsis. In other instances, this complication has not been reported. This certainly should not be interpreted to mean that it cannot occur. The risk of septicemia in hyposplenic disorders is rarely above 10 to 15%. In disorders with minimal inhibition of splenic function, the incidence of sepsis would presumably be less than the 1.5% incidence following surgical splenectomy for trauma. Considering these data, a very large number of patients would have to become asplenic before it would be likely that one would develop sepsis. Furthermore, the lack of awareness of the possibility of hyposplenia-related sepsis in many of these disorders may cause such occurrences to go unrecognized. Finally, since the risk of sepsis is probably less in hyposplenic adults as compared to children, studies on adults may underestimate the incidence of this complication in children. Many of the disorders reported to cause hyposplenia in adults have not been noted to do so in children. In instances such as celiac disease, it may take many years for the complication to manifest so that it would be unlikely for a child to manifest hyposplenia during childhood. However, in other instances, not enough children have been studied to be confident that the hyposplenia and its associated risk of sepsis are not complications that occur in children. Hyposplenia-related bacterial septicemia is a catastrophic complication. If a patient develops a disorder that is potentially associated with hyposplenia, the patient should be observed for signs of asplenia in the peripheral blood. If the technique is available, quantitation of red cell pits should be performed. If not, other studies of splenic function such as radionuclide scans should be considered, depending on the incidence of hyposplenia in that particular disorder. If evidence of asplenia develops, pneumococcal vaccine should be administered, penicillin prophylaxis should be considered, significant febrile episodes should be managed aggressively, and probably most importantly, the patient and family should be carefully educated about this complication. Most deaths from hyposplenia-related septicemia are preventable.

Clinical studies with spleen-specific radiolabeled agents

While 99mTc sulfur colloid imaging, because of its availability and convenience, remains the initial procedure of choice for spleen imaging, selective spleen scanning with damaged 99mTc-labeled RBCs can provide additional information in some cases. These cases include overlapping left hepatic lobe and suspected splenic pathology but with poor radiocolloid uptake that precludes visualization. Other indications are detection of residual splenic tissue after splenectomy, suspected asplenia, polysplenia, and situs ambiguus. The selective 99mTc-denatured RBC scan is most useful to confirm or exclude defects seen on the radiocolloid study and to detect small amounts of splenic tissue.

The spleen: development and functional evaluation

Despite the fact that the spleen has multiple functions, only one has been widely used for evaluation of the organ by imaging techniques (phagocytosis of 99mTc sulfur colloid). The usual splenic uptake of this radiocolloid can by used to determine the size, location, and integrity of the organ. A major use of splenic radiocolloid imaging has been in the study of congenital defects. Thus, eventration of the diaphragm, accessory spleens, splenogonadal fusion, the asplenia and polysplenia syndromes, and the wandering spleen are amenable to study by means of intravenously administered radiocolloid. Interference with the splenic uptake of radiocolloid can be either focal or generalized (as in functional asplenia). Imaging of the spleen has a major role in evaluating suspected trauma of the organ and in following its clinical course. The return of splenic function after splenectomy (splenosis or accessory spleens) can be documented by radionuclide imaging, and likely by hematologic techniques when the volume of tissue is sufficiently large. The detection of intrasplenic lesions is important in tumor staging and as an alerting sign to an ongoing process.