Conjoined twins (Siamese) in guinea pigs (Cavia porcellus): description of anatomopathological findings of a case of cephalothoracoonphalopagusABSTRACT
The objective of the research was to describe the physical characteristics, through X-rays and necropsy in conjoined twins (Siamese twins) of female guinea pigs (Cavia porcellus). The study sample was located in Cusco, Peru. The methodology used was descriptive. The conjoined twins of cephalothoracoonphalopagus type in guinea pigs (Cavia porcellus) were stillborn from a female guinea pig (type 1). The stillborn was subjected to radiographic evaluation and a single skull and two distinct vertebral columns were observed. Anatomopathological examination revealed the head, thoracic cavity and umbilicus as the main attachment point. They were classified as cephalothoracoonphalopagus type. After necropsy they had one head, one face, two developed eyes, and one eye in the posterior part of the skull, two nostrils, four auricular pavilions, one oral cavity plus tongue, two pairs of thoracic extremities, two umbilici. The respiratory system consisted of two well-formed nostrils, one guinea pig had no lungs, two thoracic cavities, two hearts and two diaphragms, which separated the two thoracic cavities from the single abdominal cavity. In conclusion, it is remarkable that congenital malformations occur very rarely, this malformation is rare in domestic animals. Further research on the causes of this congenital anomaly is needed.
Keywords:
siamese twins; Cavia porcellus; congenital malformation; anatomopatológicos; cephalothoracoonphalopagus
RESUMO
O objetivo da pesquisa foi descrever as características físicas, por meio de raios X e necropsia, de gêmeos siameses de porquinhos-da-índia fêmeas (Cavia porcellus). A amostra do estudo foi localizada em Cusco, Peru. A metodologia utilizada foi descritiva. Os gêmeos siameses do tipo cefalotoracoonfalópago em cobaias (Cavia porcellus) nasceram de uma cobaia fêmea (tipo 1). O natimorto foi submetido à avaliação radiográfica, e foram observados um único crânio e duas colunas vertebrais distintas. O exame patológico revelou a cabeça, a cavidade torácica e o umbigo como os principais ponto de fixação. Eles foram classificados como do tipo cefalotoracoonfalópago. Após a necropsia, eles tinham uma cabeça, uma face, dois olhos desenvolvidos e um olho na parte posterior do crânio, duas narinas, quatro pavilhões auriculares, uma cavidade oral e língua, dois pares de membros torácicos e dois umbigos. O sistema respiratório consistia em duas narinas bem-formadas, a outra cobaia não tinha pulmões; tinha duas cavidades torácicas, dois corações e dois diafragmas, que separavam as duas cavidades torácicas da única cavidade abdominal. Concluindo, é notável que as malformações congênitas ocorram muito raramente em animais domésticos. São necessárias, portanto, mais pesquisas sobre as causas dessa anomalia congênita.
Palavras-chave:
gêmeos siameses; Cavia porcellus; malformação congênita; anatomopatológicos; cefalotoracoonfalópago
INTRODUCTION
Twin pregnancy has always been the focus of attention, and two types are known: fraternal or non-identical pregnancy, which accounts for 70%; identical or from the same fertilized egg, which accounts for about 30% (Lugones-Botell and Ramírez-Bermudez, 2011). A dizygotic pregnancy results from the fertilization of two different eggs (dizygotic) or from the fertilization of a single egg that then divides to form two genetically identical embryos (monozygotic). The frequency of twin pregnancies varies; the worldwide rate of identical twin pregnancies remains stable at 3.5 percent per 1,000 people and does not appear to be related to genetic, age or environmental influences. Conjoined twins are caused by delayed and incomplete division of the identical blastoderm, usually after day 13 of fertilization. This is a sporadic phenomenon with an incidence of 1 in 50,000 to 1 in 100,000 and can only occur in monochorionic and monoamniotic pregnancies.
Mortality is very high and only in a few cases the anatomy is sufficient to allow surgical separation while preserving survival (Rodriguez-Velazquez et al., 2012; Arteaga-Yañez et al., 2016). The origin of conjoined twins is unclear but is said to be the result of an aberration during identical twin formation. In fact, identical twins themselves are considered an aberration of normal development, thus representing a more serious defect when identical twins cannot separate completely. Incomplete segregation is believed to be the result of a partial duplication in the embryonic disc before the third week of intrauterine life; wherever they are combined they are referred to as Siamese twins (Lugones-Botell and Ramírez-Bermudez, 2011).
Other authors have also suggested that conjoined twins are identical individuals derived from the same fertilized egg and monochorionic membrane, united through specific parts of their anatomy, connected by blood vessels, may have one or more organs, and have the same sex, genetically identical. They are more common in females with a frequency of 3 to 1 (Rodriguez-Velazquez et al., 2012; Ortiz et al., 2019).
The factors that cause this anomaly are currently unknown, but it should be noted that it may be related to characteristic defects of the initial line or aging of the oocyte due to a decrease in the normal differentiation capabilities, forming two differentiation centers that cannot be suppressed on either side of the other. It is also important to note that Siamese twins often have other conditions; many may be related to the site of association, but other conditions are not anatomically related (De La Ossa and Altahona, 2010).
Several authors have mentioned some risk factors for the development of twin pregnancy, such as ethnicity, maternal age, family history of twins, multiparity, etc. (Ortiz et al., 2019). To classify Siamese twins, the anatomical site of fusion is usually named, followed by the suffix pagus (pagos), from the Greek, indissoluble union. Typical fusions are named thoracic (thorax), omphalus (umbilical-abdominal), pigo (buttocks-sacrum), ischium (pelvic) and cranium (head) (Rodriguez-Velazquez et al., 2012). This classification was proposed in 1996 by Spencer and establishes 8 basic Siamese types (Spencer, 1996).
Ventral union: 87%:
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Cephalopagus (11%): They are those whose union covers from the beginning of the forehead to the umbilical region. There are four pairs of arms and legs.
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Thoracopagus (19%): Located opposite each other, these Siamese have the union at the anterior thorax level and always share the heart.
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Omphalopagus (18%): These are Siamese twins that share the umbilical region and the lower thorax, without including cardiac structures.
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Ischiopagus (11%): Ischiopagus Siamese are fused ventrally caudally from the umbilical region. They present a fused pelvis with two sacrum and two pubic symphysis, the anus and external genitalia are always involved in the union.
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Craniopagus (5%): These are Siamese twins that share any portion of the skull excluding the face and the foramen magnum. The trunks are not united.
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Piopagus (2%): Dorsally conjoined Siamese twins that share the sacrococcygeal joint, the perineal region and occasionally the spinal cord. Usually there is one anus with two rectums.
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Rachypagus (6%): These are Siamese conjoined dorsally above the sacral line.
These are twins united ventrolaterally, sharing abdomen and pelvis, with a pubic symphysis and one or two sacrum. If they have a separate thorax, they are called ditoraxic parapagus; if they have a fused thorax, they can be bicephalic or bicephalic parapagus. Cephalo-thoraco-onphalopagus is an extremely rare type of twin fused at the head, thorax, and umbilicus, but with distinct spines, limbs, and pelvis (Koreti et al., 2014). Given the low incidence of this anomaly in guinea pigs, we decided to report it because of its importance and for its knowledge. The objective of the study was to describe the physical characteristics, through X-rays and after necropsy in conjoined twins (Siamese twins) of female guinea pig (Cavia porcellus).
MATERIALS AND METHODS
The Siamese twins born, were brought from the city of Cusco-Peru (2023), the type of breeding was improved breed family (type 1), the color was bay with short and smooth hair, it is also shiny and adapts well to the body. The feed ration was based on alfalfa (Medicago sativa) and household waste (vegetables). Water was supplied by drinking troughs and the maximum climate temperature was 23°C and minimum 5°C with humidity reaching 48% at an altitude of 3,399 meters above sea level.
This sample was transported in a flask with 12% formalin to the Laboratory of Histopathology, Embryology and Animal Reproduction of the Faculty of Veterinary Medicine and Animal Husbandry of the Universidad Nacional Micaela Bastidas de Apurimac, Abancay, Peru. For the laboratory analysis, the code of ethics for research - UNAMBA was followed, as confirmed by resolution Nº 093-218-CU-UNAMBA. A radiological and anatomopathological study was made, the delivery of the Siamese twins was euthyroid with normality. The female gave birth to two male offspring (alive and healthy), and two Siamese twins (dead) of female sex. Detailed X-ray images of the Siamese twins on the right and left sides were taken with Ecoray automatic digital X-ray system (Manufacturer: China), to properly capture the skeletal structure of an anomalous individual. After that, the necropsy was performed following the methodology of Rodrigues et al. (2021), focusing on the internal organs and the shape of the twin connection with the help of a dissection equipment to observe the internal part of the animal. Then we proceeded to weigh the organs of both the thoracic and abdominal cavity OAHUS PIONER (Manufacturer: USA).
RESULTS
The female guinea pig (Cavia pocellus) gave birth to two Siamese guinea pigs with a length of 10cm in both the right and left guinea pigs. In the right lateral position, there is union at the level of the common skull and facial bones, joined by the head, thorax, and umbilicus (A); in the left lateral position, there is a single eye with two auricular pavilions and no development of the encephalon (B) (Fig. 1).
The female guinea pigs (Siamese twins) were stillborn, the mother until the presentation of this case was alive. Radiographic examination of the guinea pigs revealed a single skull, two complete and distinct vertebral columns and well-developed bones, which showed the radiopacity expected in young animals (Fig. 2).
Necropsy and photo documentation of the case were performed, the twins had a head with a single face, two well-developed eyes, and one eye in the back of the skull, two well-formed nostrils, four ear pinnae, one oral cavity with a tongue. Guinea pigs had two pairs of well-developed thoracic limbs, two umbilici, and each is continuous with the umbilical vein which is attached to the umbilical cord connected to the placenta. From the umbilical region, the body was divided into two distinct and well-developed pelvises, each containing a pair of anatomically normal limbs, tail, vulva and anus.
The respiratory system consisted of two well-formed nostrils and nasal cavities, the trachea was not observed and has two pairs of lungs. There were two thoracic cavities, two hearts and two diaphragms, which separated the two thoracic cavities, two abdominal cavities.
Newborn female guinea pigs (Siamese twins). Right lateral position (A); left lateral position (B)
X-ray of female guinea pig (Siamese twins) in right lateral position (A) and left lateral position (B)
The right lateral position showed a single oral cavity, with a tongue, two orbits, two pairs of thoracic and pelvic extremities, two pelvises, the thoracic cavity, with two hypoplastic lungs, two umbilical cords, two pairs of ovaries with their uteri with their vagina. In the left lateral position it is observed that it has only one eye, with two auricular pavilions, it presents anencephaly, it has no oral cavity, at thorax level there is presence of both lungs, the liver and two pairs of ovaries with its uterus with its vagina are observed, by the characteristics it can be said that they are Siamese cephalothoracoonphalopagus (Fig. 3).
Necropsy and documented photo of female guinea pig (Siamese twins). Right lateral position (A); left lateral position (B)
In the digestive system, neither the esophagus nor the stomach was identified in both guinea pigs, but they shared a single small intestine (33cm), then continued with a bifurcation from the large intestine where the right guinea pig reaches a length of 36 cm and the left guinea pig measures 19 cm the length of the large intestine, and then each one ends in a different rectum and anus. There were two livers with weights of 4.24 and 4.40 g from the right and left guinea pig respectively. The pancreas and spleen were absent. The twins had two anatomically well-formed genitourinary systems, the kidneys of the right guinea pig weighed 0.98 g for the right kidney and 0.97 g for the left kidney. On the other hand, the left guinea pig had 1.06 g for the right kidney and 0.97 g for the left kidney, and then each one continued with its ureters, urinary bladders and urethra. It is also observed that each guinea pig macroscopically has well-formed reproductive apparatuses with a weight of 0.46 g for the right guinea pig and 0.37 g for the left guinea pig (Table 1).
DISCUSSION
The exact cause of phenotypic abnormalities in Siamese twins remains unknown and so far, two theories have been proposed. The incomplete division theory was proposed (Zimmerman, 1967), stating that the timing of division in monozygotic twin pregnancies determines the existence of shared structures between the two fetuses and that when it occurs between days 13 and 16 after fertilization Siamese twins are produced. The second theory was proposed by Spencer, who recently hypothesized that two previously separated monoovular embryonic discs fuse at around 3 to 4 weeks of gestation (Spencer, 2000).
Although cephalopagus Siamese twins are not the most frequent of all conjoined twins, it is difficult to find case series and systematic reviews describing their characteristics and pathogenesis, perhaps due to the absence of practical surgical utility, this anomaly has been described as lethal. Regarding local statistics of these congenital anomalies in humans between 1967 and 1986, 1' 714, 952 births observed in 95 hospitals were studied in Latin America, in which 23 cases of Siamese twins were registered, of which 4 were cephalopagos, 3 parapagos, 1 ischiopagos, 5 pyopagos, 9 thoracopagos, 1 omphalopagos, 1 rachipago (Castilla et al., 1988).
It is believed that these types of deformations have been known since ancient times and were recorded due to their peculiar nature and surprisingly fantastic effects. However, when they are called Siamese twins, it is a serious defect if one of the identical twins fails to separate; the incomplete separation is believed to be the result of a partial duplication of the embryonic disc before the third week of intrauterine life (De La Ossa and Altahona, 2010).
Conjoined identical twins, called Siamese twins, can be born, representing an embryonic anomaly in which two complete or incomplete bodies are joined at one or more anatomical sites (Spencer, 2000). The prevalence of Siamese twins in animals is still unknown due to few studies. However, there are unique reports in cats (Mazzullo et al., 2009; Seavers, 2009; Rodrigues et al., 2021), dogs (Nottidge et al., 2007), goats (Binanti and Riccaboni, 2012), cattle (Ordóñez and Tovar, 2017; De La Ossa and Altahona, 2010) and guinea pigs (Cavia porcellus) at different periods and in different parts of the world (Tejml et al., 2022).
Siamese twins are considered a rare pathology affecting 1:200 monozygotic twin pregnancies, 1:900 twin pregnancies and 1: 25,000 to 100,000 births. They are more commonly observed in ruminants than in other zoological groups. The record presented here is of the type of Siamese twins’ malformation with the lowest occurrence, as thoracopagus represent 49%, omphalopagus 35%, pyopagus 18%, cephalopagus 2% together with ischiopagus with another 2% (De La Ossa and Altahona, 2010).
This suggests that there are currently no known factors causing such congenital anomalies; however, they may be related to the aging and age of the animals. This may be due to nutritional problems and poor blood flow, which are not observed in this finding (De La Ossa and Altahona, 2010). Finally, there are genetic variables, such as the possibility of inbreeding of the parents, either because of limited geographical differences in their origins, or because the original imported individuals or founding groups are similar, and because of the lack of new distant relatives. This may explain the loss of genetic variation through inbreeding, which in turn leads to the presence of certain genetic malformations or anomalies (De La Ossa and Altahona, 2010).
Congenital physical anomalies have been observed in domestic animals because of certain phytotoxins, mercury poisoning and teratogens. External causes of these anomalies also include radiation, infection, hyperthermia, hypothermia, toxic metals or adverse maternal conditions such as obesity, diabetes, iodine deficiency, etc. (Tejml et al., 2022).
In a laboratory in the Czech Republic, guinea pigs were bred with genetic lines of a pure black breed originating from Great Britain. This line was bred without inbreeding. Each guinea pig on the farm is microchipped and has a pedigree of three generations. This ensures a clear identity and background and that they receive the same level and quality of care, including feeding. Therefore, it seems unlikely that the external factors mentioned above are responsible for the anomalies. The animals are fed a balanced and high-quality ration, even the hygienic and microclimatic conditions were controlled, but despite this, Siamese twins are found. Another possible cause mentioned in the literature could be obesity (Tejml et al., 2022).
In the present report, the information on the history of the female guinea pig was not sufficient to determine the underlying etiology or pathogenesis as the rearing was in a family system without much control of external factors and internal factors to present casuistry. Newborn Siamese twins are always very interesting and occur infrequently and even more so in guinea pigs or guinea pigs, due to the large number of animals, it is remarkable that congenital malformations occur very rarely.
CONCLUSIONS
Siamese twins in newborn guinea pigs found in Cusco Peru, occurs very rarely, after X-ray radiography the Siamese twins were females joined at the upper body by a cephalothoracoanophalopagus type connection, the skeletons of both bodies were connected by a shared broad skull and sternum. Both fused bodies had their own hearts, livers, lungs.
After necropsy the twins had a head with a single face, two well-developed eyes, and one eye in the back of the skull, two well-formed nostrils, four auricular pavilions, a mouth cavity with a tongue, and a mouth cavity with a tongue. The problem with this anomaly has not yet been clearly explained, this published report would be the fifth described case of Siamese guinea pig birth worldwide. They were born in a family breeding system in Cusco - Peru in 2023.
ACKNOWLEDGEMENTS
The authors thank the Escuela Académico Profesional de Medicina Veterinaria and Zootecnia of the Universidad Nacional Micaela Bastidas de Apurímac (UNAMBA) for providing the facilities for the experimental work.
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