CLINICAL Literature Review Craniopagus: Overview and the implications of sharing a brain Jordan Squair1 1School of Kinesiology, University of British Columbia
Edited by: Amara Sarwal, Department of Psychology, University of British Columbia. Received for review January 8, 2012, and accepted February 27, 2012. Copyright: © 2012 Squair. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivates License, which permits anyone to download and share the article, provided the original author(s) are cited and the works are not used for commercial purposes or altered in any way.
Abstract Craniopagus twins, who are conjoined at the head, are uncommon and often misunderstood. While craniopagus is rare in itself, Krista and Tatiana Hogan are unique even among craniopagus twins: their brains are connected. In this review, I will explore the history of craniopagus as well as our current understanding of the malformation. Furthermore, I will discuss surgical separation techniques, classification systems, and how these have led to higher survival rates in separated craniopagus twins. Surgical separation of craniopagus twins is perhaps the most formidable of all neurosurgery operations, particularly in the presence of shared neural tissue. Krista and Tatiana fall into this daunting category. The risk of neural damage, coupled with circulatory complications, led Krista and Tatiana’s physicians to conclude a separation would be too dangerous. Consequently, Krista and Tatiana are left with a connection that is both novel to documented research and exquisitely mysterious. They possess what their pediatric neurosurgeon Dr. Doug Cochrane has called a “thalamic bridge” (Dominus, 2011a). Krista and Tatiana’s thalamic bridge will provide significant insight into the study of cognition and behaviour, and may even have significant implications to the philosophy of mind. Furthermore, their connection will be accompanied by major social change, as we must redefine our definition of what it means to be an individual. For us to understand how being part of a pair is more important than being an individual to one’s identity, we must shift our perspective and eliminate our preconceived notions of individuality. Keywords: craniopagus, conjoined twins, thalamus, brain, surgical separation
Examples of human fascination with twins high standing: they were not only great are evident through history. The Gemini warriors, but raised by gods. Conjoined constellation, known in Greek mythology as twins, though less recognized, also appear in Castor and Pollux, is arguably the most well Greek and Roman mythology. Kteotos and known set of twins. Castor and Pollux fought Eurytos, known as the Molionides, were great battles alongside Herkales and others joined at the hip and adversaries of in what became known as the Argonauts Herkales. The Molionides destroyed (Hard, 2004). The Greeks held these twins in Herkales’s armies and are responsible for
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one of the great warrior’s rare losses in must gain an appreciation of how their battle (Hard, 2004). Furthermore, Janus, the brains are connected, and objectively Roman god of beginnings and transitions, is contemplate what it means to be an depicted as having two faces. Initially Janus individual. may not resemble conjoined twins; however, a recent interview with nineteen- Modern History of Craniopagus year-old brothers Stefan and Tyler Delp, Although there are cases of conjoined twins craniopagus twins facing opposite directions, dating to the 10th century (as cited in Browd shows just how similar Janus is to conjoined et al., 2008), it was not until 1491 that the twins (Hochman, 2011). Greek and Roman first case of craniopagus was documented mythology clearly glorify twins, and to this (Browd et al., 2008). Sebastian Münster’s day, twins continue to captivate us. famous work Cosmographia universalis Krista and Tatiana Hogan are provides the first account of craniopagus craniopagus conjoined twins. Craniopagus twins (as cited in Walker & Browd, 2004). twins, a term originally coined by August While discussing Bavarian history, Münster Förster to describe twins conjoined at the mentions a pair of unique twins, joined at head (as cited in Browd et al., 2008), are a the head, who lived for ten years. Münster rare (i.e., 0.6 per million births; Bucholz, follows with an account attributing the Yoon, & Shively, 1987) and misunderstood twins’ malformation to a punishment for congenital disorder, representing only 6% of their mother’s mistakes (as cited in Browd et all conjoined twins. If born, the chances of al., 2008). Furthermore, Browd et al. (2008) craniopagus twins surviving past infancy are discuss a chapter from “On Monsters and quite low (Stone & Goodrich, 2006): 40% are Marvels,” a republished book, originally still-born (Browd, Goodrich, & Walker, 2008) written by 16th Century French surgeon and 33% die within twenty-four hours of Ambroise Paré. In the chapter entitled birth. Despite these harrowing odds, Krista “Monsters,” Paré depicts various types of and Tatiana Hogan are already beyond their “supernatural” twinning, some of which, fourth birthday. They not only survived, but curiously enough, resemble craniopagus. they are healthy and thriving. Later, Paré asserts that “[i]t is certain that While craniopagus is rare in itself, Krista most often these monstrous and marvelous and Tatiana are unique even among creatures proceed from the judgment of craniopagus twins: their brains are God…” (p 5). Fortunately, over time, this connected. Krista and Tatiana’s neural radical view towards conjoined twins began bridge will provide significant insight into the to change. study of cognition and behaviour, and might Chang and Eng, the original “Siamese even have significant implications to the twins,” embraced their malformation. They philosophy of mind. Their unique neural traveled in road shows near the beginning of connection may forever change the meaning the 19th Century – eventually becoming not of individuality and perception. In this only rich, but a new type of art (as cited in review, I will explore the history of Browd et al., 2008). Nevertheless, because craniopagus as well as our current of the rarity of craniopagus twins, even now understanding of the malformation. Through many still share Paré’s view of them as tragic this we can begin to grasp what Krista and or punished. The Delp family’s fear of Tatiana’s lives will entail. From them, we people’s ignorance and discrimination led
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CLINICAL CRANIOPAGUS Literature Review them to hide Stefen and Tyler from much of fusion of two embryonic disks. Specifically, the world. It was not until June of 2011 that Spencer (2000b) states that craniopagus they gave their first interview – at the age of twins may result from fusion of primitive nineteen (Hochman, 2011). Stefen, Tyler, neural folds. Nevertheless, without a Krista, Tatiana, and all other craniopagus concrete cause, prevention is not an option twins are so rare that the most recent and the focus must be on treatment. review shows a total of only 64 documented The precision of existent classification cases (Stone & Goodrich, 2006). The systems and their correct application are discussed history of craniopagus extensively critical for those attempting to successfully shows how craniopagus twins can be seen separate craniopagus twins, since different by some as “monsters.” Therefore, junction sites present different combating ignorance through both complications (Browd et al., 2008). The first knowledge and being mindful of existing attempt at a craniopagus classification prejudices are vital steps in removing system was made by O’Connell (1976), who ancient stereotypes associated with refuted the philosophy of classifying craniopagus twins, thus providing Krista and according to the site of cephalic junction. Tatiana with the social acceptance they Instead, he stated that depth of junction was deserve. the most important aspect in determining survival after separation. O’Connell (1976) Classification Systems and Surgical proposed a differentiation between partial Interventions and total craniopagus. Partial craniopagus, In addition to increasing social awareness, characterized by a small cephalic junction, there must be a push to increase scientific has the possibility that each cranium is still understanding of separation techniques; intact. Conversely, total craniopagus would and, if separation is not an option, how to be characterized by a wide connection: two improve quality of life for the twins. Over brains, one cranium. Additionally, O’Connell the past fifty years, craniopagus research (1976) discusses three different has had two main focuses: surgical subclassifications of total parietal separation techniques and classification craniopagus, or as he calls it, vertical systems (Browd et al., 2008; Bucholz et al., craniopagus. Type I entails the twins facing 1987; O’Connell, 1976; Stone & Goodrich, the same direction; Type II entails the twins 2006; Walker & Browd, 2004; Winston, facing the opposite direction (inter-twin 1976). Increasing our knowledge of surgical angle ≥ 140°); and Type III entails anything in separation techniques and classification between. systems is of utmost importance to advance A decade later Bucholz et al. (1987) research on craniopagus twins; however, contested O’Connell’s (1976) system, stating addressing the ongoing debate of that the difference between partial and total classification systems should precede any craniopagus described was not precise. consideration of separation techniques. A Instead, four different classifications were secondary research question, which is introduced: frontal, parietal, related to both areas of focus, is the temporoparietal, and occipital. These question of how craniopagus twins form. classifications, unlike O’Connell (1976)’s While this is unknown, Spencer (2000a) system, are dependent on the specific argues that conjoined twins result from location of the junction. Bucholz et al.’s
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(1987) classifications are junctions of either axial rotation” (p 1084). Conversely, Stone & the frontal bones, parietal bones, both the Goodrich (2006) define vertical as having a parietal and temporal bones, and occipital continuous cranium. Thus, their system is bones, respectively. Yet, literature on recent comprised of four major classifications: total separation attempts does not support vertical, total angular, partial vertical, and Bucholz et al.’s view; rather, it reinforces partial angular. classification according to O’Connell’s (1976) The most recent proposed classification system by building on it (Browd et al., 2008; scheme comes from Browd et al. (2008), Parameswari, Vakamudi, Raghupathy, & who stress the importance of including Siddhartha, 2010). In addition to this new important risk factors such as “connectivity classification, Bucholz et al. (1987) also between scalp, calvaria, dura mater, neural proposed a venous scale to classify the tissue, arterial and venous connections, amount of venous drainage interrupted deep venous drainage, and ventricular during surgery: (1) no venous drainage was anatomy, as well as atrial and venous interrupted; (2) only cortical veins were outflow” (p 5). They provide a score, divided; (3) major dural sinuses were between 10 and 28, with a higher value encountered and ligated in the course of suggesting a more difficult separation. separation (Bucholz et al., 1987). Venous Classification systems, coupled with drainage describes the extent of which a significant advancements in imaging twin’s blood may be drained from their techniques, allow surgeons to better brain, collected in a sinus, or reservoir, and understand common and unique problems then sent to the heart to be re-oxygenated. when presented with craniopagus twins If this drainage is interrupted, blood may be (Browd et al., 2008). It has been shown that prevented from leaving the brain, resulting a surgeon's awareness of shared venous in swelling which ultimately leads to neural drainage is imperative for a successful damage. This venous drainage classification separation of craniopagus twins (Bucholz et system, important to subclassify different al., 1987), and Winston (1987) proposed that cases of craniopagus, has the strongest a classification system be developed based correlation with survival and outcome of the on the “deepest shared anatomical separated twins. Classification of these structure” (p 769). Despite huge advances in systems has proven essential in separation classification there are still significant areas attempts, as the presence of a shared missing. For example, there has yet to be a venous system is now known to be the single discussion of neural connections aside from largest risk factor for fatalities (Browd et al., their presence being correlated to higher 2008). incidence of neurological deficits following Recently, Stone and Goodrich (2006) separation (Bucholz et al., 1987). added to O’Connell’s (1976) system by Furthermore, Browd et al. (2008) are the further subclassifying total and partial first to document a classification system that craniopagus into vertical and angular. More takes complicated neural, vascular, and specifically, they define total craniopagus as ventricular anatomy into account. However, the twins sharing a significant venous sinus there is still more research needed to and partial as an absence of a shared venous understand how to classify shared neural sinus. They define angular as “an inter-twin tissue. The current classification systems led longitudinal angle below 140°, regardless of to Krista and Tatiana’s shared circulatory
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CLINICAL CRANIOPAGUS Literature Review system being immediately recognized as a towards their own deep venous drainage significant risk; nevertheless, classification system (Browd et al., 2008). The process is failed to address their novel neural repeated until one twin’s drainage system connection (Dominus, 2011a). Classification completely bypasses the shared sinus, at of neural connections may prove daunting, which point the twins can be physically as variability in the connection is extreme; separated. Bucholz et al. (1987) first showed however, understanding the nature of that this method provided the lowest neural connections may give surgeons the mortality rate and best post-operative tool they need to remove the connection neural function. Huang et al. (2004) discuss a without causing neurological deficits. case in which a staged separation was not Surgical separation of craniopagus twins is a used. Serious complications arose, such as difficult task, perhaps the most formidable extreme blood loss and shock as a result of of all neurosurgery operations. Classification severe decrease in blood volume. These systems will help surgeons be aware of complications can be fatal, and they posed common problems, but surgeons must have extreme challenges to the surgeons and a plan in place and be ready to tackle a host anesthesiologists. By performing a staged of obstacles once the twins are on the operation, the surgeon avoids the most operating table. common complication associated with Classification systems and imaging separating craniopagus twins: disastrous techniques aside, enhanced surgical and bleeding due to a shared venous drainage anesthetic techniques may be the most system (Browd et al., 2008). important factors contributing to the Although staged separation was a key decreasing mortality rates seen in separated breakthrough in the surgical separation of craniopagus twins (Browd et al., 2008; craniopagus twins, carefully planned Bucholz et al., 1987; Girshin et al., 2006). anesthetic management is crucial if the Browd et al. (2008) indicate the importance twins are to survive. Girshin et al. (2006) of classifying surgical risk factors in order to discuss the substantial benefits of using a determine mortality and the extent of staged separation and the challenges it surgery required. They then point to poses to anesthesiologists. Namely, enhancing surgical techniques, stating that craniopagus twins must be put under and in the presence of a shared venous sinus, a woken back up multiple times – each time staged separation is of great importance. In with significant risk of complication. This is this series of surgeries – often six to eight – particularly troublesome since craniopagus the surgeon’s goal is to remove one of the twins often have other pulmonary and twins from the shared sinus. This is done by cardiac complications (Girshin et al., 2006). slowly cutting bridging veins from the twin Additionally, if a shared circulatory system is that will be removed from the sinus; the present, medicine provided to one twin will surgeon must not rush this process. Cutting affect the other twin while under anesthesia too many bridging veins in one surgery may (Parameswari et al., 2010). These problems result in fatal bleeding (Browd et al., 2008). are significant but can be partially addressed After each surgery, the venous system of the by a strong pre-operative plan, the use of twin being removed will show increased two separate anesthesia teams, and strong blood pressure, resulting in angiogenesis, communication (Browd et al., 2008). which is the formation of a new path Another major complication may arise
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in surgery that is often missed by current (Dominus, 2011a). Krista and Tatiana share imaging techniques, and is not currently sensory information. To share every sensory addressed in existent classification systems modality passing through the thalamus (Browd et al., 2008): shared neural tissue. allows them to not only feel what each feels Shared neural tissue significantly decreases but even see out of each other’s eyes. A fine the chances of optimal neural function after example of this emerges in an interview of separation (Bucholz et al., 1987). Oddly, this the girls and their mother (Dominus, 2011b). risk factor has rarely been discussed in the Their mother covers Krista’s eyes and holds literature. The enormous complexity of a a plush pony in front of Tatiana. She then neural connection is daunting; however, asks Krista what she is holding and Krista current research must begin to approach replies, “pony.” In the New York Times this issue and how it may be addressed in article, “Could Conjoined Twins Share a separation attempts. As craniopagus cases Mind?” Susan Dominus (2011a) describes an are rare in humans, this research may need unpublished study performed by Dr. to begin with animal models. In the case of Cochrane when the girls were just two- Krista and Tatiana Hogan, separation posed years-old. While recording too many risks. Not only do they share electroencephalography, or brain waves, cerebral circulation (possibly a shared from both girls, Dr. Cochrane covered venous sinus) but also a complex neural Krista’s eyes and flashed a light in front of connection, a bridge on which information Tatiana. Increased electrical activity from can go from one girl to the other. both girls’ brain’s visual areas was recorded. The test also worked when the girls switched The Thalamic Bridge roles (Dominus, 2011a). Surface Krista and Tatiana possess what their electroencephalography is imprecise in its pediatric neurosurgeon Dr. Doug Cochrane ability to localize where activity is happening has called a “thalamic bridge” (Dominus, but the fact that there is increased activity in 2011a). To appreciate the significance of both recordings is incredible. this, a current understanding of the role of Krista and Tatiana’s ability to share the thalamus is essential. Blumenfeld (2010) sensory information is extraordinary; introduces the thalamus as “an important however, the thalamus does more than relay centre” (p 35). Pinel (2011) adds that simply act as a relay centre. As stated by “the most well understood thalamic nuclei Pinel (2011), sensory relay nuclei are only a are the sensory relay nuclei – nuclei that portion of the nuclei in the thalamus and receive signals from sensory receptors, describe merely one of its functions. process them, and then transmit them to Although the exact mechanisms are still the appropriate areas of sensory cortex” (p unclear, the reciprocal connections from the 66). Dr. Cochrane describes the way in which thalamus to cerebral cortex are heavily Krista and Tatiana are unique: when sensory involved in moderating consciousness. information travels to their thalamus it Blumenfeld (2010) poses a theoretical branches into two routes. Krista and system, “the consciousness system,” that Tatiana’s thalami receive neural inputs, and regulates level of consciousness. He process and relay them to the appropriate discusses three aspects of this system: brain area. The inputs also cross the alertness, attention, and awareness. These thalamic bridge to the other girl’s thalamus three aspects are all, in part, mediated by
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CLINICAL CRANIOPAGUS Literature Review nuclei in the thalamus such as the thalamic through someone else’s eyes.” The reticular nucleus, thought to preserve emotional repercussions of this ability are, at attention by gating information (Blumenfeld, this time, a mystery; however, through 2010). Accordingly, it could be that as Krista observation, Krista and Tatiana’s and Tatiana age, it will become apparent relationship may serve as an example of how that their levels of consciousness, which may empathy is expressed in its truest form. They affect spiritual understanding, self- will feel each other’s pain and may struggle actualization, and perception, stay very to differentiate their own sensations from similar. As the thalamus is crucial in their sister’s sensations. Krista and Tatiana consciousness and sensory information will struggle to find individual identity – as processing, damage to it would be we know it. Their version of individual detrimental to Krista and Tatiana. This risk of identity will, perhaps, be as half of a pair. damage, coupled with circulatory They are described as using the word “I” to complications, led their physicians to refer to the other twin; however, they are conclude a separation would be too aware they are two separate people dangerous. Consequently, Krista and (Dominus, 2011a). Krista and Tatiana’s Tatiana are left with a connection that is conception of “I” may be different from both novel to documented research and everyone else’s. exquisitely mysterious. The twins’ inability to differentiate between the personal and their sister may Continued Observation and Social be one behavioural consequence of their Issues neural bridge; in that, their inability to Krista and Tatiana’s thalamic bridge seems distinguish between their own sensations to connect one or more of their sensory and those of their sister may confuse their modalities. It might also connect their levels sense of identity. Continued observation of of consciousness and perceptions of the Krista and Tatiana may result in the finding world. Scientific exploration of this of other behavioural consequences caused connection holds the potential to change by their thalamic bridge, which could further modern society’s view of individualism. our understanding of the thalamus and Specifically, by observing Krista and Tatiana individuality. Furthermore, the sharing of as they age, their unique concept of identity identity, levels of consciousness, and will become more apparent. Due to their perhaps thoughts, has implications for our connection, Krista and Tatiana will spend understanding of the philosophy of mind. If their entire life, as a pair, being extremely Krista and Tatiana share these complex different from most people. Thus, as a pair, notions of identity and thought – commonly they paradoxically exemplify individualism. associated with “the mind” as opposed to However, these girls face a challenge in “the body” – it implies the mind may be individuality that has never been addressed. shared through a physical bridge. The mind Although Krista and Tatiana have separate may not be separate from the body, but brains and personalities, they may share a housed within it. Although the notion that common perception of their surroundings, the mind and brain are one is not new, Krista which makes them rare even amongst and Tatiana’s case may further strengthen craniopagus twins. Consequently, they our understanding of how and where the embody the expression “seeing the world mind is housed in the brain. Despite the
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endless scientific advances Krista and Reddy, S., Staffenberg, D., & Wasnick, J. (2006). Anesthetic management of staged Tatiana may provide, one must remember: separation of craniopagus conjoined twins. they are individual girls, but, more Pediatric Anesthesia, 16, 347-351. importantly, an individual pair of girls. For us doi:10.1111/j.1460-9592.2005.01712.x to understand how being part of a pair is Hochman, G. (2011). A rare pair: Nineteen-year-old conjoined twins from South Jersey, who thrive more important than being an individual to as brothers and best friends, give their first-ever one’s identity, we must shift our perspective interview. Philadelphia Inquirer. and eliminate our preconceived notions of Hard, R. (2004). The routledge handbook of Greek individuality. Also, it is crucial that mythology: Based on H.J. Rose’s handbook of Greek mythology. New York, NY: Routledge. researchers be aware of the ethical Huang, W.Q., Fang, J.Y., Xiao, L.C., Jiang, X.P., Xia, complications coupled with pursuing J.H., Feng, X., & Jiang, N. (2004). Anesthetic research on the girls. Apart from possible management for separation of craniopagus twins. Acta Anaesthesiologica Scandinavica, developmental consequences, it may 48, 919-921. doi:10.1111/j.1399- enhance the social stigma they already face. 6576.2004.00444.x Additionally, the question of their voluntary Koppes, L. L. & Pickren, W. (2006). Historical consent must also be taken into account. perspectives in industrial and organizational psychology. Mahwah, NJ: Erlbaum Krista and Tatiana will face challenges arising O’Connell, J.E. (1976). Craniopagus twins: surgical from the possession of an ability no one in anatomy and embryology and their the world can fully understand. They implications. Journal of Neurology, simultaneously epitomize individuality as a Neurosurgery & Psychiatry, 39, 1-22. doi:10.1136/jnnp.39.1.1 pair while facing individual struggles never Paré, A. (1982). On Monsters and Marvels. Chicago, before seen. IL: University of Chicago Press. Parameswari, A., Vakamudi, M., Raghupathy, V., & Siddhartha, R. (2010). Anaesthetic Declaration of Conflicting Interests management of total craniopagus twins for The author declared they have no conflicts magnetic resonance imaging and cerebral of interests with respect to their authorship angiography. British Journal of Anaesthesia, or the publication of this article. 105, 368-370. doi:10.1093/bja/aeq165 Pinel, J.P.J. (2011). Biopsychology (8th ed.). Boston, MA: Allyn & Bacon. References Spencer, R. (2000a). Theoretical and analytical Blumenfeld, H. (2010). Neuroanatomy through embryology of conjoined twins. Part I: clinical cases (2nd ed.). Sunderland, MA: Embryogenesis. Clinical Anatomy, 13, 36-53 Sinauer Associates, Inc. Spencer, R. (2000b). Theorectical and analytical Browd, S.R., Goodrich, J.T., & Walker, M.L. (2008). embryology of conjoined twins. Part II: Craniopagus twins. Journal of Neurosurgery, 1, Adjustments to union. Clinical Anatomy, 13, 1-20. doi:10.3171/PED-08/01/001 97-120. Bucholz, R.D., Yoon, K.W., & Shively, R.E. (1987). Stone, J.L. & Goodrich, J.T. (2006). The craniopagus Temporoparietal craniopagus: Case report and malformation: classification and implications review of literature. Journal of Neurosurgery, for surgical separation. Brain, 129, 1084-1095. 66, 72-79. doi:10.3171/jns.1987.66.1.0072 doi:10.1093/brain/awl065 Dominus, S. (2011a). Could conjoined twins share a Walker, M. & Browd, S.R. (2004). Craniopagus twins: mind? The New York Times. embryology, classification, surgical anatomy, Dominus, S. (2011b, May 25). Could conjoined twins and separation. Child’s Nervous System, 20, share a mind? [Video File]. Retrieved from 554-566. doi:10.1007/s00381-004-0991-6 http://video.nytimes.com/video/2011/05/13/ma Winston K.R. (1987). Craniopagi: Anatomical gazine/100000000814707/two-united-as- characteristics and classification. one.html Neurosurgery, 21, 769-781. Girshin, M., Broderick, C., Patel, D., CHacko, S.,
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