Craniopagus Twins
David J. Dunaway
Noor Ul Owase Jeelani
DEFINITION
Craniopagus twins (conjoined at the head; CPT) are extremely rare, occurring in about 1:2.5 million live births. They account for 2% to 6% of all conjoined twins.1,2,3
Partial (localized) or total
Angular or vertical (types I to III)
The degree of union varies, and shared tissues may include skin, bone, dura, brain, and venous drainage system.
The possibility of separation is dependent on the degree and pattern of tissue sharing and whether or not this allows the possibility of leaving an uninjured well-vascularized brain.
ANATOMY
Partial CPT is less common than total CPT and may involve any number of tissue layers including the dura. The cortical gyri may interdigitate but are usually separable. Significant intracranial dural venous cross circulation is rare. Union is usually either frontal or occipital.
FIG 1 • Classification of craniopagus.
Total vertical CPT has a longitudinal stovepipe configuration, and the three O’Connell subclasses describe the angulation of the twins (see FIG 1).
The scalp derives its blood supply from both twins allowing skin flaps to be raised across the twins to aid reconstruction.
The calvarium is fused. Both sagittal sutures are absent and replaced by a ring suture running circumferentially around the cylindrical skull.
The dura separating the two brains is single layered and usually incomplete.
Cerebral arterial supply is generally separate, although minor degrees of crossover occur.
The cerebral venous drainage is shared and complex. The superior sagittal sinus is absent from both twins and is replaced by a complete or incomplete circumferential venous sinus (CVS). Mixing of the venous circulations occurs and blood generally drains preferentially to one twin (FIG 2).5
The brains abut in a flattened, tilted plane that does not align with the circumferential cranial suture. Areas of cerebral cortex may be fused.
Total angular CPT form a heterogeneous group, and there are several classifications. Classification is generally by area of union. Winston proposed a grading system based on the deepest structure involved, which is prognostically useful.6
 FIG 2 • CT angiography demonstrating the circumferential venous sinus (CVS) and venous drainage across the twins. |
PATIENT HISTORY AND PHYSICAL FINDINGS
Diagnosis is usually made antenatally. Planning separation of CPT relies primarily on information gained from imaging. The history and physical examination are important in eliciting physiological effects in planning surgical access.
Extracranial and general effects include the following considerations:
Airway: It may be difficult to position the twins to protect both airways. Airway support or tracheostomy may be required.
Circulation: Total CPT results in significant mixing of venous blood that usually drains preferentially to one twin. This has two major consequences:
Cardiovascular: Increased venous return increases cardiac load and in severe situations can lead to cardiac failure. The unequal venous drainage and fluid distribution generally results in hypertension in one twin and hypotension in the other. This asymmetrically shared blood supply has significant anesthetic implications.
Renal: Large volumes of urine are generally produced by the hypertensive twin, whereas the other produces very low volumes of urine.
Nutrition: In situations where there is significant venous shunting, the high metabolic demands placed on the twin with high cardiac output generally produce an underweight twin.
IMAGING
Detailed multimodality imaging provides key information for general management and is essential for surgical planning (FIG 3).7
CT: Visualizes bony morphology, sutural pattern, and the relationship of the brain, skin, and dura to the skull
MRI: Delineates brain and dural anatomy indicating areas of possible cortical fusion and dural defects
Digital subtraction angiography: Provides anatomical information about arterial and venous systems and the extent and direction of vascular crossover between the twins. This modality also characterizes the relationship between the deep and superficial venous drainage systems of the brain for planning separation.
FIG 3 • Radiological imaging. Twin A is at the top and Twin B at the bottom. A. MRI delineates brain anatomy and areas of cortical confluence. B. CT with 3D reconstruction delineates skin bone and vascular anatomy. C. Angiography showing injection from twin A. D. Injection from twin B.
CT angiography: Characterizes the anatomy of the dural venous sinuses
NONOPERATIVE MANAGEMENT
It may not be possible to separate some pairs of CPT because of unfavorable vascular anatomy and brain fusion. Even more straightforward cases carry a risk of brain damage and death. The decision to attempt separation is based on an assessment of risk to the two individuals, in addition to ethical and social issues, and may be different for each individual. There are several examples of unseparated twins who live fulfilling lives. A decision not to separate brings its own challenges. These include potential psychosocial difficulties as life progresses and the physiological challenges associated with a shared circulatory system.
SURGICAL MANAGEMENT
CPT require complex multidisciplinary management and often present with cardiac, renal, and general pediatric problems. General care is complicated by difficulties in positioning. When planning separation, consideration must be given to the issues of each twin, in turn, followed by shared issues.
Many approaches for the separation of CPT have been described, but they essentially fall into two categories, a single-stage separation often preceded by an episode of tissue expansion or a multistage approach.9,10,11 There is now general agreement that a multistage separation encourages adaptation in the blood supply to the brain and reduces the risk of cerebral damage and is the procedure of choice for total extensive CPT.12 This chapter will describe our experience with multistage separation.Related posts:
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