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The authors discuss the successful separation of craniopagus conjoined twins at Great Ormond Street Hospital and the role of the ophthalmologist in such cases.


Craniopagus conjoined twins are extraordinarily rare, occurring in only one in 2.5 million births and representing only 2-6% of conjoined twins [1,2]. Rarer still are male craniopagus twins, representing only 30% of craniopagus twins [2]. Sadly, around 40% of craniopagus twins are stillborn or die during labour, while a further third die within 24 hours [2].

These highly complex cases present unique challenges to the entire multidisciplinary team, including the ophthalmologist. As these cases are so rarely encountered, it is helpful to share experiences and lessons learned for each case.

Yigit and Derman

On 21 June 2018, conjoined twins Yigit and Derman were born in Antalya, Turkey [3]. They were delivered by caesarean section at 32 weeks. Their father had built a special crib which could accommodate the twins, who were unable to face the same direction or face each other [3]. Their development and quality of life was severely affected by their condition, but surgically separating such twins represents an extremely difficult task, often associated with devastating results. Harvey and colleagues [4] reviewed 14 attempted surgical separations from 1995 to 2015 and found that over a third of cases (n=5) were unsuccessful, either resulting in the death of both twins (n=1) or one twin (n=4). Multi-stage operations were associated with the highest chance of success [4].


Figure 1: Three-dimensional soft tissue reconstruction demonstrating craniopagus malformation.


Figure 2: Three-dimensional reconstruction of the brains of the craniopagus twins.


On 2 December 2019, the twins were referred to Great Ormond Street Hospital (GOSH), London. The treatment at GOSH was funded by Gemini Untwined charity [5]. They were diagnosed with total vertical (Type 2) craniopagus malformation, meaning that the two twins were joined at the top of the head and faced approximately 180 degrees away from each other, as shown in Figure 1. The two brains were merged together, as can be appreciated in Figure 2, with multiple shared venous sinuses and arterial crossover vessels. It was decided that the safest way to proceed was with staged surgical separation, featuring the insertion of tissue expanders to produce enough skin to cover the two scalps, followed by three procedures to separate the brains and blood vessels and reconstruct the skulls.


Figure 3: Tissue expanders in situ to produce sufficient skin for separation and craniofacial reconstruction.


Modified ophthalmic examination

The ophthalmic examination was challenging, as conventional methods were not feasible for this case. Our modified approach is described in detail in our recently published paper in the Journal of Surgical Case Reports [6]. Specifically, we adopted a modified approach using forced-choice preferential looking, portable slit-lamp biomicroscopy, indirect ophthalmoscopy and optical coherence tomography (OCT).


Figure 4: Handheld OCT image acquisition in operating theatre.


To the best of our knowledge, this represents the first use of handheld OCT in craniopagus twins [6]. We used the Envisu C2300 handheld OCT device (Leica Microsystems, Wetzlar, Germany) to examine the optic nerve heads and foveae (Figure 4). Handheld OCT findings were normal in both twins [6].

The main ophthalmic abnormality was due to high right brow positions in both twins secondary to scalp shortage. This caused right exposure keratopathy secondary to lagophthalmos in both twins, which could be appreciated well during examination under anaesthesia using the Keeler Portable Slit-lamp (Keeler Ltd, Windsor, UK). This was successfully treated with topical lubricants but will likely require full correction with surgery in the future.


Figure 5: Twins post-separation surgery, pictured undergoing physiotherapy.


Surgical separation

The twins were separated on 28 January 2020 (Figure 5) and discharged from GOSH on 9 June 2020 back to Turkey. This case was covered in a Channel 4 documentary, Conjoined Twins [7]. This represents the fourth separation of craniopagus twins at GOSH and the largest global experience of successful separations of craniopagus twins.

"To the best of our knowledge, this represents the first use of handheld OCT in craniopagus twins."

The surgical treatment was supported by detailed neuroimaging, 3D modelling and virtual reality simulation. Over 100 professionals across more than 15 disciplines contributed to Yigit and Derman’s treatment. After five weeks of tissue expansion, their three surgical separation procedures totalled 36 hours of surgery and the entire surgical process took seven weeks – quicker than the previous three sets separated at GOSH. This minimised the risk of complications due to a potentially prolonged hospital stay. Following separation, right brow positions grossly improved in both twins.


It is extremely rare for an ophthalmologist to be asked to assess craniopagus conjoined twins – indeed, most ophthalmologists may never see such a case throughout their careers. Notably, we have learned that handheld OCT is feasible and clinically valuable in such cases, not only to provide a detailed baseline assessment of the optic nerve heads and foveae, but also to monitor and exclude any potential pathology during the course of treatment. Indeed, when one twin displayed altered visual behaviour in the postoperative period, the handheld OCT excluded any new retinal or optic nerve pathology. Furthermore, assessing vision in young preverbal children is challenging, so the ability to examine structural morphology using serial handheld OCT examinations is clinically valuable.

As luck would have it, in August 2019, Noor ul Owase Jeelani, Senior Neurosurgeon, was holidaying with his family in Antalya, Turkey – the hometown of Yigit and Derman, where he was able to review them and speak with the family and the Turkish medical team. The case had been referred to him four weeks previously [5]. He and his colleague, Professor David Dunaway, Professor of Craniofacial Surgery at GOSH, had just started their charity, Gemini Untwined, after recently separating Pakistani craniopagus twins, Safa and Marwa [8]. Gemini Untwined was able to raise the necessary funds and mobilise resources to help Yigit and Derman [5].

The main focus of Gemini Untwined is to treat craniopagus conjoined twins, but the associated research, technology and expertise can be applied to treating more common craniofacial abnormalities. Gemini Untwined has brought together leading clinicians, scientists, engineers and other professionals with one common goal – to defy the odds and give craniopagus twins the chance to return home as two separate, healthy children.

  • Craniopagus twins require a specialised approach by ophthalmologists to optimise clinical management.
  • Handheld OCT is feasible A valuable in craniopagus twins.
  • Meticulous planning and multi-staged surgery can deliver positive results.
  • There is a wider need for ophthalmologists to adapt to changing patient challenges, using technology where appropriate to optimise investigations.


1. Stone JL, Goodrich JT. The craniopagus malformation: classification and implications for surgical separation. Brain 2006;129(Pt 5):1084-95.
2. Great Ormond Street Hospital for Children NHS Foundation Trust. Second set of rare conjoined twins separated at Great Ormond Street Hospital in less than 12 months. June 2020:

3. Hurriyet Daily News. Conjoined Turkish twins celebrate first birthday. June 2019:

4. Harvey DJ, Totonchi A, Gosain AK. Separation of Craniopagus Twins over the Past 20 Years: A Systematic Review of the Variables That Lead to Successful Separation. Plast Reconstr Surg 2016;138(1):190-200.
5. Gemini Untwined. Yigit and Derman’s Story. June 2020:

6. Rufai SR, Gore S, Handley SE, et al. Enhanced neuro-ophthalmologic evaluation to support separation of craniopagus twins. J Surg Case Rep 2021;2021(2): rjaa606.
7. Channel
4 News. Conjoined twins: Doctors separate brothers joined at the head. June 2020:

8. Gemini Untwined. Safa and Marwa’s Story. June 2019:

(All links last accessed February 2021)



The authors would like to thank the parents for granting permission to publish this information; and Luke Smith for contributing the 3D reconstructions (Figures 1 and 2) and Patricia McHugh, on behalf of Gemini Untwined, for contributing photographs (Figures 3 and 5) for this article. Funding: Gemini Untwined; The Medical Research Council (London, UK) (grant no.: MR/N004566/1); Dr Rufai is funded by a National Institute for Health Research (NIHR) Doctoral Fellowship Award. This work is supported by the NIHR Great Ormond Street Hospital Biomedical Research Centre. This case report presents independent research funded by the National Institute for Health Research (NIHR), MRC and Gemini Untwined. The views expressed are those of the author(s) and not necessarily those of Gemini Untwined, the MRC, the NHS, the NIHR or the Department of Health and Social Care.


Declaration of competing interests: None declared.




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Sohaib Rufai

Great Ormond Street Hospital and University of Leicester Ulverscroft Eye Unit.

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Sri Gore

Clinical and Academic Department of Ophthalmology, Great Ormond Street Hospital for Children, London, UK.

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Noor ul Owase Jeelani

Craniofacial Unit, Great Ormond Street Hospital for Children, London, UK & UCL Great Ormond Street Institute of Child Health, London, UK.

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