screened for intestinal malrotation Data suggest that this is likely not necessary As discussed earlier, there is a high proportion of isomeric patients who will have intestinal malrotation, but the incidence of volvulus is quite low Yet-to-bepublished data demonstrate that those who experience volvulus tend to experience symptoms and develop volvulus in the first months of life Thus observing patients closely, and imaging only when symptoms arise, has become an increasingly more popular and safe approach Those without symptoms should not undergo upper gastrointestinal series routinely If an asymptomatic patient does undergo such testing for indications such as gastrostomy tube placement, and intestinal malrotation is noted, a prophylactic Ladd procedure may reasonably be deferred If symptoms occur, a Ladd procedure can be done at that time This is a particularly useful approach in those who require a Blalock-Taussig shunt Those who already have a Blalock-Taussig shunt at the time of Ladd procedure or those who undergo placement of such a shunt shortly after Ladd procedure are at increased risk for thrombosis of the Blalock-Taussig shunt.88,93–96 Growth and feeding only in those with isomerism has not been the sole focus of studies to this point, but it is anecdotally known that feeding difficulties are noted in a fair number of patients with isomerism In fact, 25% of infants with isomerism will require either a nasogastric or gastrostomy tube In a majority of these patients, the tube can be removed by 1 year of age Immune System The immune system is often affected in those with isomerism In fact, splenic morphology was initially used to segregate so-called heterotaxy into subsets Although we now understand that splenic morphology is not the best means by which to divide patients with isomerism, it is still important to understand the splenic morphology in the setting of isomerism Traditional segregation of isomerism has been into the subsets of asplenia and polysplenia, although a proportion of patients with isomerism will have a solitary spleen Thus all three of these arrangements are possible Absence of the spleen, or asplenia, is often noted in those with right isomerism, while presence of multiple spleens, or polysplenia, is often noted in those with left isomerism A solitary spleen is located in a small proportion of either subset of isomerism.1,3,48,97 In addition to abnormal splenic morphology, those with isomerism may also have abnormal thymic morphology Abnormal thymic involution is found in nearly 20% of patients with isomerism at the time of necroscopy.48 Splenic function is obviously absent in those with isomerism and asplenia, but splenic function may also be diminished or absent either in those with isomerism and polysplenia or in those with a solitary spleen.98 In those with polysplenia, 12% will have abnormal splenic function, while in those with a solitary spleen, 11% will have abnormal splenic function Due to this and likely other factors, 25% of those with isomerism will have a documented episode of bacteremia An overwhelming majority of these episodes of bacteremia are nosocomial and occur before 2 years of age Mortality in isomeric patients with bacteremia ranges between 10% and 58% Those who do experience mortality believed to be a result of bacteremia are generally 21 months of age.97,99–103 Bacteremia is due to encapsulated organisms in nearly 70% of those with isomerism Apart from abnormal splenic morphology, a low number of immunoglobulin memory B cells also increases the risk of bacteremia in those with isomerism.97,104 Because of the increased risk of bacteremia in patients with isomerism and the increased risk of mortality associated with this bacteremia, special precautions should be taken Based on data from patients with sickle cell anemia, in whom splenic function is abnormal, antibiotic prophylaxis may be helpful The limited data thus far available also support the use of antibiotic prophylaxis While it seems intuitive that splenic function should be determined early in life to help guide the initiation of antibiotic prophylaxis, currently available splenic function testing is not accurate in the first few years of life Testing prior to 2 years of age is not reliable by current methodology.101 Thus all patients with isomerism, even those with multiple spleens or a solitary spleen, should be placed on antibiotic prophylaxis with amoxicillin, given as 20 mg/kg per day, divided twice daily or one time daily For those not tolerating enteral medications, ampicillin can be used instead, with the transition made to amoxicillin once enteral medications are tolerated.105,106 For those with multiple spleens or a solitary spleen, splenic function testing should be done at 2 years of age Pitted red blood cell testing is the preferred method, due to increased sensitivity and specificity, but Howell-Jolly body testing can be utilized as well.107–110 If splenic function is normal, antibiotic prophylaxis may be discontinued If splenic function is abnormal, however, antibiotic prophylaxis should be continued until 5 years of age Antibiotic prophylaxis may be discontinued in all isomerism patients at 5 years of age based on data from isomerism patients and sickle cell patients.97,111 In addition to antibiotic prophylaxis, vaccinations are also important in patients with isomerism The standard vaccination schedule for children, as established by the American Academy of Pediatrics, should be used However, a few additional vaccinations should also be administered Those with isomerism should receive a 23-valent polysaccharide pneumococcal vaccination after 2 years of age in addition to (not in place of) the 13-valent polysaccharide pneumococcal vaccination Meningococcal vaccination should also be slightly altered in those with isomerism, with Hib-MenCY-TT being administered at 2 months, 4 months, 5 months, and 12 months of age.112 Febrile episodes in those with isomerism should lead to routine evaluation All isomeric patients with a temperature of 38.5°C or greater should be evaluated either in the outpatient setting or in the emergency department Evaluation should include a complete blood count with manual differentiation, C-reactive protein, and blood culture Additional optional evaluation may include chest radiographs and urine culture Those who appear healthy can be discharged home after being administered a single dose of intramuscular ceftriaxone and appropriate follow-up while blood cultures are monitored Those who appear ill should receive intravenous antibiotics and be admitted Any patient with isomerism with a positive blood culture should complete a full course of antibiotics, which can be done either inpatient or outpatient Those admitted to the hospital can be discharged when they appear well, with completion of antibiotics possibly as an outpatient Those who are admitted and placed on antibiotic therapy because they appeared ill but who have negative blood cultures can have antibiotics stopped after 48 hours.111,113 Genitourinary System Anatomic anomalies of the genitourinary system have been noted in isomerism These include horseshoe kidney, ectopic ureters, ureteral duplication, cystic kidney, solitary kidney, and cloacal duplications What have yet to be delineated are any functional implications of isomerism on kidney function ... patients with isomerism The standard vaccination schedule for children, as established by the American Academy of Pediatrics, should be used However, a few additional vaccinations should also be administered Those with isomerism