Role of biplane digital subtraction angiography, and 3D rotational angiography in craniopagus twins: A case report, detailed pictorial evaluation, and review of literature.

Cranially conjoined twins (craniopagus) are regarded as one of the rarest human malformations. Craniopagus represents 2 to 6% of conjoined twins and is the rarest type of disorder. A conventional angiogram with three dimensions is needed to confirm the exact extent of sharing of the arterial / venous tree. 3D angiography was first proposed by CORNELIUS and advanced into clinical practice by VOIGT in 1975. We present a case of craniopagus vertical type II twins, evaluated for cerebral circulation.

Introduction

Cranially conjoined twins (craniopagus) are regarded as one of the rarest human malformations. Craniopagus represents 2 to 6% of conjoined twins and is the rarest type of disorder.[1] A conventional angiogram with three dimensions is needed to confirm the exact extent of sharing of the arterial / venous tree. 3D angiography was first proposed by CORNELIUS[2] and advanced into clinical practice by VOIGT in 1975.[2] We present a case of craniopagus vertical type II twins, evaluated for cerebral circulation.

Case Report

TWIN I and TWIN II both female twins aged four (D.O.B - 15/10/2003) were referred to our institution for digital subtraction angiography. 3D angiographic evaluation was done for the craniopagus vertical type II twins, to assess the cerebral vasculature and to identify the different variations in cerebral circulation, which is essential for surgical planning.

An angiogram was performed by selective, individual, as well as simultaneous injections of internal, external, and vertebral arteries of both twins. A 3 D rotational angiogram was also performed, to study the anatomic variations in detail.

Simultaneous and sequential injections of both the twins was performed by positioning TWIN I on the caudal end of the angiography table, head being turned in the right lateral position with nose to right, while TWIN II was positioned on the cranial end of the table with head in Anteroposterior position.

Table

Cerebral circulation

Four-year-old craniopagus twins, both female, were evaluated for their detailed cerebral circulation. The angiographic machine used for the same was Advantax LCN + (GE Biplane system). Retrograde seldingers method, through right femoral puncture of both twins, was used as a technique to study the variations in the arterial and venous cerebral circulation of the craniopagus twins.

TWIN I:

The predominant venous drainage of TWIN I was through the left Transverse-Sigmoid system, draining out through the left internal jugular vein and through the circular sinus into TWIN II's Transverse-Sigmoid Jugular system bilaterally.

The deep venous system was not identified. The arterial as well as the capillary drainage was normal.

TWIN II:

TWIN II had venous drainage through the circular sinus into the Transverse-Sigmoid

Jugular system bilaterally and to the occipital sinus. A significant portion of the venous drainage was shunting into TWIN I's left transverse sinus. The deep venous system was not identified clearly in this twin also.

The external carotid angiogram of TWIN II showed a significant crossover of the external carotid arterial territory, to supply TWIN I's scalp [Figures 1–8].

Figure 1

Craniopagus vertical type II twins

Figure 8

Venous drainage is through the circular sinus into Transverse - Sigmoid -Jugular system bilaterally and the occipital sinus.A signifi cant portion of the venous drainage is shunted into Twin I s left transverse sinus. Deep Venous system is not identifi ed clearly

Internal carotid angiogram showing normal arterial phase(A) and capillary phase (B)of the twin I

Showing the venous drainage of the twin I through the left transverse sigmoid system(arrow head) and circular sinus(arrow) into the twin II s transverse sigmoid jugular system bilaterally

Internal carotid angiogram showing the normal arterial(A) and capillary phases(B) of the twin II

Venous drainage is through the circular sinus(arrow) into Transverse - Sigmoid -Jugular system bilaterally and the occipital sinus. Deep Venous system is not identifi ed clearly

External carotid angiogram of twin II shows signifi cant cross over of ECA territory to supply Twin I scalp

Simulataneous and sequential injections of both the twins showing normal arterial and capillary phases

Discussion

Conjoined twins are rare and the estimated prevalence in the literature varies widely from 1:50,000 to 1:200,000.[3] An increased prevalence is observed in parts of Southeast Asia and Africa, with reported occurrence ranging from 1:14,000 to 1:25,000.[4] Forty to 60% of conjoined twins are stillborn and almost 35% of live births do not survive even for 24 hours.[4]

The craniopagus type (joined at the head) is exceedingly rare, with an incidence of one in 2.5 million births.[1] The conjoined twins are monozygotic, monoamniotic, and monochorionic. The chorion differentiates approximately four days after fertilization and the amnion differentiates approximately eight days after fertilization.[5] A conjoined twin occurs as a result of the failure of complete separation (fission) of a single fertilized ovum between 13 and 17 days of gestation. Due to the incomplete division of the embryonic disc of the blastocyst, conjoining occurs in the second week.

The other theory states that the abnormality is due to the result of fusion of two separate embryos, with the junction occurring in the open cranial neuropore before the fourth week after fertilization.[6] Conjoined twins are always genetically identical and share the same sex. Females are more commonly affected, with a male / female ratio of 1:4.[7] These twins can be joined at the vertex, at the side, or at the forehead; the vertical type being the most common. O’Connell's classification denotes three anatomical types for vertical craniopagus, based on relative facial orientation (type 1: face same direction; type 2: face opposite direction (140 – 180 degrees) and type 3: intermediate angle of rotation of the long axis of one head on that of the other).[89] This congenital defect results in an area of absent cranial cutaneous ectoderm (scalp) and ectomeninx of varying severity and extent in the region where the developing telencephalic vesicles meet.

The accurate assessment of cerebral circulation is crucial for surgical planning. Digital Subtracted Angiography (DSA) with Biplane and 3D is very important for the assessment of this complex vasculature.

In our case the predominant venous drainage is through the circular sinus into the Transverse-Sigmoid-Jugular system bilaterally and the occipital sinus, which is demonstrated on the injection of TWIN II. Hyperdynamic circulation is seen in the TWIN II.

Conclusion

Digital subtraction angiogram with biplane and 3D rotation is essential to evaluate the complex vascular anatomy and anatomical variations in such cases, as it gives a complete picture of the entire circulation, which is required to take any further steps in the treatment planning of craniopagus twins.