Manifestations of bodily isomerism - Cardiovascular Pathology

Cardiovascular Pathology 25 (2016) 173–180

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Cardiovascular Pathology

Original Article

Manifestations of bodily isomerism Rohit S. Loomba a,⁎, Muhammad M. Ahmed b, Diane E. Spicer c,d, Carl L. Backer e, Robert H. Anderson f a

Children's Hospital of Wisconsin, Medical College of Wisconsin, 9000 Wisconsin Avenue, Milwaukee, WI Ziauddin University, 4/B, Shahrah-e-Ghalib, Block 6, Clifton, Karachi, 75600, Pakistan c University of Florida Department of Pediatric Cardiology, 1600 SW Archer Road, Gainesville, FL d Johns Hopkins All Children's Heart Institute, 501 6th Avenue, St. Petersburg, FL e Lurie Children's Hospital, Feinberg School of Medicine, 225 E Chicago Avenue, Chicago, IL f Institute of Genetic Medicine, Newcastle University, Central Parkway, Newcastle upon Tyne, Tyne and Wear NE1 3BZ, United Kingdom b

a r t i c l e

i n f o

Article history: Received 10 November 2015 Received in revised form 27 December 2015 Accepted 10 January 2016 Keywords: Isomerism Heterotaxy Hydrocephalus Bronchial Spleen Infection

a b s t r a c t We report the findings present in 49 postmortem specimens from patients with so-called heterotaxy, concentrating on those found in the extracardiac systems of organs. Also known as bodily isomerism, we suggest that it is important to segregate the syndromes into their isomeric subtypes to be able to make inferences regarding likely extracardiac and intracardiac findings to allow for proper surveillance. We demonstrate that this is best done on the basis of the atrial appendages, which were isomeric in all the hearts obtained from the specimens available for our inspection. The abdominal organs do not demonstrate isomerism, and they show variable features when compared to the isomeric atrial appendages. © 2016 Elsevier Inc. All rights reserved.

1. Introduction Occurring in approximately 1 in 10,000 live births, so-called heterotaxy is known to be characterized by mirror imagery of the bronchi in the same individual, in other words bronchial isomerism [1–6]. It was also demonstrated some time ago that, when assessed on the basis of the extent of the pectinate muscles relative to the atrioventricular junctions, there is also evidence of isomerism of the atrial appendages [7]. Not all authorities, however, accept the notion that isomerism also exists within the heart [8]. Moreover, although the abdominal organs are not located within their expected position in the setting of heterotaxy, there is minimal evidence of abdominal isomerism. The presence of the overall abnormal anatomical findings, nonetheless, has significant functional implications, not least because splenic function is known to be disturbed even in the setting of multiple spleens [9]. Intestinal malrotation is also known to be an associated problem [10–19]. An appreciation of the relationships between the findings in the thoracoabdominal organs and the intracardiac findings can allow for proper surveillance and, when possible, for early intervention. Proper understanding, however, requires segregation of isomerism, or heterotaxy, into its subtypes. So as to assess the relationships between cardiac and noncardiac findings, therefore, we have examined archived No sources of funding for this study ⁎ Corresponding author. E-mail address: [email protected] (R.S. Loomba). http://dx.doi.org/10.1016/j.carpath.2016.01.003 1054-8807/© 2016 Elsevier Inc. All rights reserved.

postmortem specimens diagnosed on the basis of appendage morphology but shown subsequently to be obtained from patients known to have so-called heterotaxy. This has permitted us to combine the information provided by examination of the specimens with that obtained from the original postmortem reports. In this way, we have been able to characterize the cardiac findings in the subsets of right as opposed to left isomerism and to determine the associations and differences between these findings with those in the remaining systems of organs. We discuss here how best to describe the findings in the various systems of organs so as most efficiently to convey the functional implications of the pertinent cardiac anatomic data. 2. Methods Using the sequential segmental approach, we analyzed the hearts, and thoracoabdominal organs when available, obtained from patients known to have so-called heterotaxy. The autopsy material is held in the Farouk S. Idriss Cardiac Registry at the Ann & Robert H. Lurie Children's Hospital in Chicago, IL. Specimens had been archived from the 1940s and continue to be added in the present day. Bronchial morphology was assessed on the basis of the length of the bronchi, also using the pattern of branching of the bronchial tree relative to the pulmonary arteries. Short and eparterial bronchi were considered to be morphologically right, while long and hyparterial bronchi were considered to be morphologically left [3–6]. We also assessed the lobation of the lungs, taking trilobed lungs to be morphologically right and bilobed

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lungs to be morphologically left. Within the heart, we used the extent of the pectinate muscles relative to the atrioventricular junctions to distinguish between morphologically right and left atrial appendages, as described previously by Uemura and associates [7]. This approach follows the principle established by Van Praagh and his colleagues and dubbed the morphological method [20], namely, that structures within the heart should be defined on the basis of their most constant components and not according to other features that themselves might have variable. We then assessed the connections of the systemic and pulmonary veins, the atrial septum, the atrioventricular junctions, the ventricular mass, the ventriculoarterial junctions, and the arrangement of the intrapericardial arterial trunks. We also took note of additional extracardiac findings, utilizing the reports from the original postmortem examination when the archived organs other than the heart were not available. The spleen was identified as being absent, multiple, or single. When multiple spleens were present, we ascertained whether they were left or right sided. With regard to the stomach, liver, pancreas, and gallbladder, each organ was again described as being either right, left, or midline. We took particular note of evidence for intestinal malrotation, specifically the presence of a short mesentery. The presence or absence of renal anomalies, abnormalities of the reproductive system anomalies, and cerebral anomalies were also noted. These were coded as either being present or absent, with specific details obtained when available. Clinical data contained in the original reports were also used to determine the presence or absence of bacteremia or fungemia documented by cultures immediately prior to death or done at the time of postmortem examination. We performed chi-square analysis for variables of interest, including bacteremia or fungemia, fatty liver, hepatic fibrosis, intestinal malrotation, and brain anomalies. Chi-square analysis was also performed to compare categorical variables, using SPSS Version 20.0 (Chicago, IL). Frequencies are reported as percentages or fractions.

Fig. 1. A heart from a patient with left isomerism viewed from the base of the heart. Note the atrial appendages are morphologically left bilaterally. The appendages are finger-like with a narrow attachment to the venous component (double-headed red arrows). The pectinate muscles are confined to the appendages and do not extend around the atrioventricular junction with a smooth vestibule on both sides. No Eustachian valve is appreciated in this heart. A persistent left superior caval vein drains to the coronary sinus. There is also a common atrioventricular junction with tissue connecting the superior and inferior bridging leaflets across the crest of the ventricular septum, resulting in two orifices.

3.1. Left isomerism

thrombosis of the pulmonary arterial system nor evidence if tracheobronchitis was encountered (Table 2). In nine tenths of the patients, multiple spleens were present (Fig. 4). These were left sided in x patients and right sided in the remainder. In one patient, however, the spleen was absent. No data regarding splenic function had been listed at the time of postmortem examination or reported in the clinical summaries (Table 2). The stomach was left sided in seven tenths of the cohort, with the liver positioned in the midline in two fifths, right sided in two fifths, and left sided in one fifth. The gallbladder was right sided in three fifths and left sided in the remainder. The pancreas was described as being left sided in three fifths and right sided in the remainder (Table 2). Another one sixth was found to have biliary atresia (Table 2). Intestinal malrotation was present in one third, although volvulus was neither present nor described as being present during life in any patient (Table 2). Abnormal thymic involution had been noted in one sixth, but no evidence was found for brain anomalies or anomalies of the reproductive or renal systems (Table 2).

We summarize the cardiac findings in Table 1. Details of these findings, along with those obtained from specimens held in two additional archives, are also described in detail elsewhere. In brief, cardiac findings in the setting of isomeric left appendages included the presence of either separate or common atrioventricular junctions. Several of the hearts with a common atrioventricular junction had separate right and left atrioventricular valves, in other words ostium primum defects (Fig. 1). The majority of the hearts possessed a coronary sinus and showed interruption of the inferior caval vein with azygos continuation, along with symmetrical drainage of the pulmonary veins. Most had concordant ventriculoarterial connections with spiraling arterial trunks (Table 1). We failed to find an abnormal arrangement of the coronary arteries in any patient with left isomerism. Evidence of myocardial ischemia was noted in 14.3%, albeit with no evidence of coronary thrombosis in any patient. Endocardial or myocardial fibrosis was also observed in 14.3% (Table 2). In all the hearts with left isomerism, the bronchial morphology was also isomeric left (Fig. 3). In the majority, bronchial morphology was concordant with pulmonary lobation, although one patient had lungs bilaterally with solitary lobes. Neither

Fig. 2. This heart with isomerism of the right atrial appendages is viewed from the base of the heart. The atrial appendages are bilaterally morphologically right. Note the pectinate muscles extending around the atrioventricular junction to the crux of the heart (red arrow).

3. Results We had access to a total of 49 specimens obtained from patients shown subsequently to have so-called heterotaxy. The initial diagnosis of cardiac isomerism had been made by assessing the extent of the pectinate muscles within the atrial appendages relative to the right and left atrioventricular junctions (Fig. 1). In this way, we were able to show that 12 specimens (24%) showed evidence within the heart of left isomerism (Fig. 1), with 37 (76%) showing evidence of right isomerism (Fig. 2 and Table 1).


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Table 1 Cardiac findings present in the cohort segregated into left and right isomerism based on the morphology of the atrial appendages Left isomerism (n=12) Bronchial morphology Morphologically left bronchus bilaterally Morphologically right bronchus bilaterally Usual bronchial lateralization Mirror imaged bronchial lateralization Other pattern (see the text) Pulmonary morphology Morphologically left lungs bilaterally Morphologically right lungs bilaterally Usual lung lateralization Single-lobed lungs bilaterally Single-lobed right lung and bilobed left lung Atrial appendage morphology Morphologically left appendages bilaterally Morphologically right lungs bilaterally Right-sided superior caval vein present Left-sided superior caval vein present Drainage of left-sided superior caval vein Coronary sinus Roof of left-sided atrium Drainage of inferior caval vein Azygos vein Left-sided atrium Right-sided atrium Drainage of hepatic veins Inferior caval vein Left-sided atrium Right-sided atrium Bilateral atria Coronary sinus present Drainage of pulmonary veins Infradiaphragmatic Supracardiac Mixed Symmetrical (ipsilateral atria) Left-sided atrium Right-sided atrium Midline atrial roof Common atrioventricular junction present Number of atrioventricular orifices 1 2 Pulmonary atresia present Ventriculoarterial connections Concordant Discordant Double-outlet right ventricle Double-outlet indeterminate ventricle Single indeterminate ventricle Position of aorta in relation to pulmonary artery Anterior Anterior, rightward Anterior, leftward Posterior, rightward Posterior, leftward Side by side, leftward Side by side, rightward Ventricular topology Left handed Right handed Single indeterminate ventricle Aortic arch sidedness Left Right Interruption of the aortic arch present Coarctation of the aorta present Eustachian valve present Terminal crest present Atrial septal defect present Abnormal coronary artery distribution present Direction of cardiac apex Leftward Rightward Midline

Right isomerism (n=37)

P value b.0001

100% 0% 0% 0% 0%

0% 91% 5% 2% 2

90% 0% 0% 10% 0%

7% 86% 4% 0% 3%

100% 0% 84% 47%

0% 100% 82% 66%

44% 56%

0% 100%

84% 5% 11%

0% 42% 58%

11% 17% 56% 16% 90%

66% 11% 23% 10% 0%

0% 0% 0% 53% 16% 31% 0% 79%

18% 14% 2% 0% 26% 38% 2% 98%

47% 53% 5%

94% 6% 50%

68% 11% 21% 0% 0%

2% 56% 32% 4% 6%

5% 37% 11% 11% 0% 15% 21%

8% 54% 17% 2% 2% 7% 10%

53% 47% 0%

42% 50% 8%

95% 5% 5% 21% 0% 0% 95% 14%

70% 30% 0% 2% 82% 100% 98% 19%

53% 42% 5%

68% 32% 0%

b.0001

b.0001

.671 .257 b.0001

b.0001

b.0001

b.0001 b.0001

.006 b.0001

.001 b.0001

.376

.390

.030

.102 .006 b.0001 b.0001 .470 .903 .170

(continued on next page)

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Table 1 (continued)

Splenic anatomy Absent Multiple Solitary Location of stomach Left sided Right sided Midline Location of liver Left sided Right sided Midline Location of gallbladder Left sided Right sided Midline Pancreatic location Left sided Right sided Midline Intestinal malrotation present

Left isomerism (n=12)


7% 93% 0%

85% 9% 6%

67% 33% 0%

53% 41% 6%

25% 42% 33%

13% 28% 59%

40% 50% 10%

23% 68% 9%

58% 42% 0% 55%

53% 41% 6% 74%

P value b.0001

.562

.288

.540

.672

.226

Table 2 Noncardiac findings present in the cohort segregated into left and right isomerism based on the morphology of the atrial appendages

Gender Male Female Bronchial morphology Morphologically left bronchus bilaterally Morphologically right bronchus bilaterally Usual bronchial lateralization Mirror imaged bronchial lateralization Other pattern (see the text) Pulmonary morphology Morphologically left lungs bilaterally Morphologically right lungs bilaterally Usual lung lateralization Single-lobed lungs bilaterally Single-lobed right lung and bilobed left lung Splenic anatomy Absent Multiple Solitary Location of stomach Left sided Right sided Midline Location of liver Left sided Right sided Midline Location of gallbladder Left sided Right sided Midline Pancreatic location Left sided Right sided Midline Intestinal malrotation present Abnormal thymic involution Abnormal coronary artery branching present Endocardial or myocardial fibrosis present Evidence of myocardial ischemia Coronary artery thrombi present Pulmonary thrombi present Tracheobronchitis Fatty liver Fibrotic liver Brain anomalies present Renal anomalies present Genital anomalies Biliary atresia Bacteremia/fungemia

Left isomerism (n=19)


58% 42%

77% 23%

100% 0% 0% 0% 0%

0% 91% 5% 2% 2

90% 0% 0% 10% 0%

7% 86% 4% 0% 3%

7% 93% 0%

85% 9% 6%

67% 33% 0%

53% 41% 6%

25% 42% 33%

13% 28% 59%

40% 50% 10%

23% 68% 9%

58% 42% 0% 55% 10.0% 14.3% 12.5% 12.5% 0% 0% 16.7% 0% 16.7% 0% 0% 0% 5.0% 30.8%

53% 41% 6% 74% 24.0% 19.4% 16.7% 8.0% 4.3% 10% 10.5% 25.0% 5.9% 46.7% 14.3% 14.3% 0% 13.3%

P value

.230 b.0001

b.0001

b.0001

.562

.288

.540

.672

.226 .350 .670 .779 .700 .575 .385 .687 .176 .420 .063 .686 .686 .005 .177


Bacteremia or fungemia, however, had been observed in one quarter of patients (Table 2). 3.2. Right isomerism The cardiac findings are again summarized in Table 1. Cardiac features included universal absence of a coronary sinus. All the hearts exhibited totally anomalous pulmonary venous connection, even when the pulmonary veins connected to the heart (Fig. 5). The majority had presence of a common atrioventricular junction but usually guarded by a common atrioventricular valve. The ventriculoarterial connections were typically discordant or double-outlet right ventricle. Within the atrial chambers, there was evidence in all hearts of bilateral terminal crests and usually additional presence of a Eustachian valve (Table 1). An abnormal coronary arterial arrangement was noted in one eighth of the hearts. In two patients, there was a single coronary artery, which arose from sinus #1. In another patient, there were two coronary arteries arising from separate orifices from sinus #1, with a third coronary artery arising from sinus #2. Evidence of myocardial ischemia had been noted in one patient. One patient, who died at 17 years of age, was found to have multiple old myocardial infarctions, with thrombus evident in his coronary arteries. This was the patient with three separate coronary arterial orifices described above. Endocardial or myocardial fibrosis was present in one sixth of the hearts (Table 2). The bronchi were bilaterally morphologically right (Fig. 6) in all but two of the patients, the outstanding individuals having usual bronchial arrangement. A majority (87%) of the lungs were also bilaterally, morphologically right, but 10% of the patients had bilateral, morphologically left lungs, while bilateral, single-lobed lungs were found in two patients. Pulmonary arterial thrombosis was present in 10%, and evidence for tracheobronchitis in 25% (Table 2). The spleen was absent in three quarters of patients. Multiple spleens identified in 15% of the patients, being left sided in x and right sided in y. The spleen was solitary and left sided in 9% of the patients (Table 2). The stomach was on the left side of the abdomen in 55% of patients and right sided in the remainder. The liver was mostly midline or symmetric in half the patients, to the right in 28%, and to the left in the remainder. The gallbladder was right sided in 63%, left sided in 32%, and in the midline in 5%. The pancreas was left sided in 55%, right sided in 40%, and midline in 5% (Table 2). Intestinal malrotation was present in two thirds of the cohort, albeit with no reported evidence of volvulus (Table 2). Biliary atresia was not noted in any of the patients with right isomerism (Table 2). Abnormal thymic involution was noted in one sixth, and brain anomalies were noted in two fifths. These consisted of hypoxic neuronal change, cerebellar atrophy, hydrocephalus, frontoparietal lobe infarction, right frontal lobe infarction, encephalomalacia, hemorrhage, and presence of a single ventricle. The patient who had evidence of multiple old myocardial infarctions with coronary arterial thrombosis also had infarction of the frontoparietal and right frontal lobes. A single kidney was present in two patients, and anomalies of the reproductive system, specifically a bicornuate uterus, were present in one patient (Table 2). Bacteremia or fungemia was noted in one tenth of patients with right isomerism (Table 2). 3.3. Associations between findings We carried out univariate analysis seeking to identify features associated with intestinal malrotation, brain anomalies, and bacteremia or fungemia. No specific findings were found to be associated with intestinal malrotation (P=.126). Features associated with brain anomalies were bronchial anatomy and fatty liver. Those with bilateral, morphologically right bronchi were more likely to have brain anomalies (P = .040), as were those with fatty liver (P=.001). Brain anomalies were only present in patients with right isomerism.

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Features associated with bacteremia or fungemia were the atrioventricular junctional anatomy, coarctation of the aorta, and the direction of the cardiac apex. Those with two atrioventricular orifices were at higher risk for bacteremia or fungemia (P=.041) as were those with coarctation of the aorta (P=.014) and rightward cardiac apex (P=.029). Neither splenic anatomy (P = .119) nor abnormal thymic involution (P=.592) was associated with bacteremia or fungemia. 3.4. Age at death The median age of death for patients in our cohort was 3 months (range 1 week to 17 years). The median age of death in those with right isomerism was 1 month, while for those with left isomerism, it was 6 months (P=.688). None of the associated features was found significantly to impact on age at death. When median age of death was assessed on the basis of splenic morphology, those with multiple spleens died at 6 months, those with a solitary spleen at 3 weeks, and those with absence of the spleen at 3 months (P=.615). Those with intestinal malrotation had a median age of death of 3 months, compared to 6 months in those without (P = .792). Median age of death for those with fatty infiltration of the liver was 4 months, while the median age of death for those with hepatic fibrosis was 8.6 years. 4. Discussion Although some authorities continue to doubt the presence of isomeric features within the heart, all of our specimens had been identified as having isomeric atrial appendages during the triage of a large archive of hearts held at Lurie Children's Hospital [8]. This was achieved by assessing the extent of the pectinate muscles relative to the atrioventricular junctions, following the approach taken initially by Uemura and colleagues [7], and as dictated by the so-called “morphological method” [20]. When we then checked the cardiac findings either with the arrangement of the remaining autopsied organs or with the original autopsy reports, it emerged that all the specimens had been obtained from patients with so-called heterotaxy. In the past, the isomeric arrangements were often considered to represent “partial situs inversus”. When using the morphology of the appendages to determine atrial arrangement, however, we were also able to distinguish between the 49 sets of organs included in this study as showing isomerism from 5 additional sets in which there was evidence of overall mirror imagery when compared to the usual arrangement. It is mirror imagery when compared to normality that is the essence of so-called “situs inversus”. In the patients with the mirror-imaged arrangements, all the thoracoabdominal organs, including the atrial appendages, were on the opposite sides of the body when compared to the usual arrangement, often still described as “situs solitus”. The situation in the patients with the isomeric organs, in contrast, is that the right-sided and leftsided bronchi and atrial appendages are mirror images of each other in the same individual. When studying the specimens available from the Lurie archive, we found excellent concordance between bronchial morphology and the arrangement of the atrial appendages. The associations, however, were not complete. Thus, in two patients with isomeric right atrial appendages, we found normal bronchial morphology. The intracardiac findings, nonetheless, were as anticipated for right isomerism. Concordance with relation to pulmonary lobation was a poor correlate, as was the correlation between thoracic and abdominal morphology. In the past, it was usual to segregate so-called heterotaxy into the subsets of “asplenia” and “polysplenia” [21]. Our current findings, along with the evidence available from scrutiny of our original autopsy reports, point to the fallibility of this approach. In several of the original reports, we encountered descriptions of presence of the spleen in the so-called “asplenia syndrome”. Uemura and his colleagues have since demonstrated that splenic morphology is poorly correlated with the subsets of so-called “heterotaxy” when segregated according to the morphology

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Fig. 3. Bronchial tree from a patient with left isomerism viewed from its posterior aspect. The bronchi are long and have an acute angle of takeoff bilaterally. The pulmonary artery on either side crosses the ipsilateral bronchus before it branches making both bronchi hyparterial.

of the atrial appendages [7,22]. For the cardiologist, therefore, it is the morphology of the atrial appendages that provides the best guide to the anticipated intracardiac findings. The structure of the appendages will also provide the best indicator of the type of isomerism present for the pediatrician. Despite the protestations of influential authorities [4], the evidence continues to mount showing that isomerism does exist within the heart. By manipulating the genes known to be responsible for producing morphologically rightness and leftness, for example, molecular biologists have now produced mice with unequivocally isomeric right and left atrial appendages [23,24]. In the abnormal mice, it is only the appendages that are uniformly isomeric, although the venoatrial connections show some degree of symmetry. This is also the situation in our studied hearts. As was suggested by Van Praagh and his colleagues, it is the most constant components of any cardiac structure that should be used for definition when the heart is malformed [20]. Since it is the appendages and the extent of the pectinate muscles that are the most constant atrial components, it follows that

they should be used to discriminate between morphologically rightness and leftness. Although it is only the atrial appendages that are truly isomeric, nonetheless, the patterns of venous drainage provide additional evidence of the influence of the genes determining laterality. Thus, the pulmonary veins, in the normal heart, are morphologically left structures. It is not surprising, therefore, that totally anomalous pulmonary venous connection should be a feature of right isomerism, with the veins connecting in anatomically abnormal fashion even when returning to the heart. Universal absence of the coronary sinus is similarly explained on the basis of this venous channel being a morphologically left structure, even though it drains to the morphologically right atrium. Moreover, since the inferior caval vein is a morphologically right structure, return of the abdominal venous return through the azygos system is an expected feature of left isomerism. It is harder, however, to explain the features of the atrioventricular junctions, ventricular mass, and ventricular outflow tracts on the basis of isomerism but thus is almost certainly because the laterality genes influence both halves of the developing ventricular loop in comparable fashion, this feature also explaining why there is no evidence of ventricular isomerism. Van Praagh himself, however, has continued to argue that the syndrome of “heterotaxy” should be approached in terms of “situs ambiguus”, stating that, in this setting, “the type of atrial situs is undiagnosed” [25,26]. This is surprising since, when using the principle established by Van Praagh himself, the morphology of the atrial appendages now permits unequivocal recognition of “atrial situs”. Although we found excellent concordance between the bronchial morphology and the atrial appendages in our cohort, there was no demonstrable pattern for the abdominal organs, even though they were typically arranged in abnormal fashion. It did not prove possible to interpret the patterns in terms of isomerism or mirror imagery in the same individual. It may be considered that “situs ambiguus” is an appropriate term for describing such abdominal arrangements. In our opinion, such usage would imply uncertainty regarding the location of each organ, which is not the case. It is of greater value simply to describe the position of each organ individually, thus avoiding terms that, in and of themselves, produce unnecessary ambiguity. It is the findings within the thoracic organs, therefore, that permit segregation of so-called heterotaxy into the two isomeric subsets. It is this information that will be of greatest significance for future genetic counseling. Differentiation between the two subsets also permits inferences to be made regarding the likely intracardiac findings. The

Fig. 4. The abdominal organs from a patient with left isomerism. Panel A demonstrates a right-sided stomach near which there are multiple spleens noted on both sides of the dorsal mesogastrium. Panel B demonstrates a midline liver with a midline gallbladder. There is a right-sided stomach.


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Fig. 6. Bronchi from a patient with right isomerism viewed from the posterior aspect. The bronchi are bilaterally short with the pulmonary arterial branch (yellow arrows) extending to the lower lobe beneath the first bronchial branch rendering the bronchi eparterial.

Fig. 5. This heart with isomerism of the right atrial appendages is viewed from the anterior aspect. The left pulmonary veins drain in a supracardiac fashion to the left brachiocephalic vein that then drains into the right-sided atrium via the right-sided superior caval vein. The right-sided pulmonary veins are draining below the diaphragm to the portal venous system, resulting in mixed pulmonary venous return. The inferior caval vein is left sided and there are hepatic veins draining into the right-sided, morphologically right atrium.

situation is less clearcut when considering the remaining systems of organs. It is now well established, for example, that functional asplenia should be anticipated in all patients with isomerism. Once isomerism is identified, therefore, prophylactic antibiotics can and should be started in a timely fashion, even in the presence of left isomerism, with the patients likely to have multiple spleens. In these patients, or even those with a solitary spleen, functional testing with Howell-Jolly bodies, or pitted red blood cells, can result in false negative results in the first months of life. We found intestinal malrotation in almost one third of our patients, but with no statistically significant difference noted between those with right and left isomerism. Most of those who have previously studied malrotation in the setting of heterotaxy have discriminated patients on the basis of splenic status. Thus, although Hill and colleagues found a higher incidence of malrotation in those with “asplenia”, the findings may have differed had they sought to visualize the atrial appendages or bronchial morphology to aid them in their classification [10]. We did not identify any other findings, either cardiac or noncardiac, to be significantly associated with intestinal malrotation other than the presence of overall isomerism. Our findings also fail to show that the risk of volvulus is high in either group. Previous studies, nonetheless, have demonstrated a risk of volvulus among those with heterotaxy and malrotation to be minimal, although a study by Yu and colleagues demonstrated a 10% risk [10–19]. There is now emerging evidence that at least two fifths of those with isomerism lie on the ciliopathy spectrum, although it is abnormal ciliary motion and not ultrastructure that is the underlying defect [27]. As cilia are found in nearly every organ of the body, such ciliary abnormalities can have an impact on most systems. Studies have already demonstrated

increased frequency of sinupulmonary symptoms in those with isomerism and ciliary dyskinesia, as well as an increased requirement for ventilatory support [28]. Mouse models of ciliopathies, furthermore, have demonstrated fatty infiltration of the liver in mice with mutations in the Bbs4 gene [29]. Various ciliopathies are associated with liver fibrosis [30–34]. Biliary atresia, also associated with isomerism, is similarly on the ciliopathy spectrum. Abnormal cholangiocyte cilia have been noted in the livers of patients with both syndromic and nonsyndromic biliary atresia [35]. The cholangiocyte cilia possess a chemical signaling role based primarily on response to intracellular calcium and cyclic adenosine monophosphate. If this pathway is disrupted, there can be a decrease in intracellular calcium, with a concurrent increase in cyclic adenosine monophosphate, which can lead to abnormal biliary development [36–39]. The abnormal position of the liver may be a result of abnormal right–left signaling by abnormal ciliary motion of nodal cilia in the primitive stages of embryologic development [40]. Renal anomalies, present in 2% of the current cohort, have also been associated with a variety of ciliopathies. These include polycystic kidney disease, both autosomal recessive and autosomal dominant, nephronophthisis, and oral-facial-digital syndrome [41]. In the kidney, specifically for autosomal recessive polycystic kidney disease, there is abnormal ciliary signaling due to functional impairments in the function of fibrocystin. The signaling derangements impact cell orientation such that cells align in oblique or perpendicular fashion, resulting in dilation or cyst formation [42]. Such concepts are important not only for understanding the underlying mechanisms of the abnormalities but also because mutations that alter expression or signaling in pathways, such as the Hedgehog pathway, may be amenable to treatment [43]. Brain anomalies were present in one sixth of our patients, all of whom had right isomerism. Hydrocephalus has been associated with ciliary dyskinesia in mice and humans. Mutations in genes such as PCDP1 and CFAP54 in mice result in decreased ciliary beat frequency and cilia-driven flow and can manifest as hydrocephalus [44]. Ciliopathies such as Joubert, Meckel-Gruber, and Bardet-Biedel

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syndromes further underscore how abnormal ciliary function can lead to alterations in cortical formation and lead to neurodevelopmental impairments [42,45,46]. A majority of mutations leading to ciliopathies with central nervous system anomalies are currently demonstrated to be loss-of-function mutations although further study is likely to identify more gain-of-function mutations. Currently identified genes are involved in progenitor cell development, neuronal migration, neuronal differentiation, and neuronal connectivity [47]. It could be significant, therefore, that some patients in our cohort also had neuronal changes due to longstanding hypoxia. We recognize that our study is limited by the fact that all our specimens were obtained from an historical archive. Frequencies of anomalies, therefore, may differ from those in patients who survive longer. Additionally, data were not available for each endpoint, so the frequencies we have reported may be underestimates. The statistical analysis is also underpowered due to the low sample size. Future work requires investigation of additional specimens to help further power statistical analysis and functional ciliary analysis that could, in turn, help further elucidate the mechanisms of anomalies. Additionally, some of the associations noted, such as the absence of a right-sided superior caval vein, do not have intuitive explanations. It is possible that, with a larger cohort, these findings would no longer demonstrate a statistically significant association. 5. Conclusion So-called heterotaxy is best segregated on the basis of the atrial appendage, which are the most constant feature in the setting of isomerism. This allows for inferences to be made regarding the likely intracardiac findings and has significance for past and future genetic studies. Noncardiac findings are present in several organ systems and are likely the result of ciliary dyskinesia. Acknowledgements There are no acknowledgements. References [1] Loomba RS, Hlavacek AM, Spicer DE, Anderson RH. Isomerism or heterotaxy: which term leads to better understanding? Cardiol Young 2015:1–7. [2] Loomba R, Shah PH, Anderson RH. Fetal magnetic resonance imaging of malformations associated with heterotaxy. Cureus 2015;7:e269. [3] Loomba RS, Pelech AN, Shah PH, Anderson RH. Determining bronchial morphology for the purposes of segregating so-called heterotaxy. Cardiol Young 2015:1–13. [4] Partridge JB, Scott O, Deverall PB, Macartney FJ. Visualization and measurement of the main bronchi by tomography as an objective indicator of thoracic situs in congenital heart disease. Circulation 1975;51:188–96. [5] Partridge J. The radiological evaluation of atrial situs. Clin Radiol 1979;30:95–103. [6] Van Mierop LH, Eisen S, Schiebler GL. The radiographic appearance of the tracheobronchial tree as an indicator of visceral situs. Am J Cardiol 1970;26:432–5. [7] Uemura H, Ho SY, Devine WA, Kilpatrick LL, Anderson RH. Atrial appendages and venoatrial connections in hearts from patients with visceral heterotaxy. Ann Thorac Surg 1995;60:561–9. [8] Van Praagh R, Van Praagh S. Atrial isomerism in the heterotaxy syndromes with asplenia, or polysplenia, or normally formed spleen: an erroneous concept. Am J Cardiol 1990;66:1504–6. [9] Nagel BH, Williams H, Stewart L, Paul J, Stumper O. Splenic state in surviving patients with visceral heterotaxy. Cardiol Young 2005;15:469–73. [10] Hill SJ, Heiss KF, Mittal R, Clabby ML, Durham MM, Ricketts R, et al. Heterotaxy syndrome and malrotation: does isomerism influence risk and decision to treat. J Pediatr Surg 2014;49:934–7 [discussion 7]. [11] Nakada K, Kawaguchi F, Wakisaka M, Nakada M, Enami T, Yamate N. Digestive tract disorders associated with asplenia/polysplenia syndrome. J Pediatr Surg 1997;32: 91–4. [12] Choi M, Borenstein SH, Hornberger L, Langer JC. Heterotaxia syndrome: the role of screening for intestinal rotation abnormalities. Arch Dis Child 2005;90:813–5. [13] Ferdman B, States L, Gaynor JW, Hedrick HL, Rychik J. Abnormalities of intestinal rotation in patients with congenital heart disease and the heterotaxy syndrome. Congenit Heart Dis 2007;2:12–8.

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