P4A044: Earliest Known Craniopagus Parasiticus Magnetic Resonance Imaging with Associated 3D Model

Introduction: Craniopagus conjoined twins are a rare anomaly of asymmetrical union between two skulls, excluding the face and the foramen magnum. A subset of this entity, craniopagus parasiticus, is characterized by the underdevelopment of one twin. Fetal magnetic resonance imaging (MRI) is increasingly used to diagnose and manage complex fetal conditions. We present the earliest reported fetal MRI of craniopagus parasiticus twins with 3-dimensional (3D) modeling used for understanding of anatomy and patient counseling.

Case Description: A 37-year-old G4P0030 with 3 first trimester miscarriages underwent in-vitro fertilization (IVF). An ultrasound (US) performed at 5 weeks and 4 days (5w4d) confirmed an intrauterine pregnancy with gestational sac and yolk sac, along with a subchorionic hematoma (SCH) measuring 3.6 cm. A repeat US at 6w4d showed a single live intrauterine gestation and known SCH. However, her US at 7w0d GA showed what appeared to be monochorionic diamniotic twins. A follow up ultrasound at 8w4d suggested monochorionic monoamniotic (MCMA) twins with fetuses in proximity and a SCH measuring 6.39 cm. Her US at 12w0d confirmed MCMA craniopagus conjoined twins with the smaller twin having an underdeveloped torso, absent legs, and no obvious umbilical cord insertion. Fetal MRI was performed at 14w1d confirmed craniopagus parasiticus twins without discrete fusion of brain tissue. These images, specifically those resulting from T2-weighted single-shot fast spin echo and balanced steady state gradient echo sequences, were used to generate virtual 3D models (Mimics, 3-matic, Materialise; Meshmixer, Autodesk; Daz Studio Pro, Daz 3D). This study clarified anatomy of the skulls and brain tissue, as well as revealed unusual proximal branching of the umbilical cords wherein the two cords were fused close to the placental insertion, resulting in the smaller twin having a very short cord. This information was used for operative planning as well as patient education. At 16w0d, an echocardiogram found an absence of cardiac activity in both twins and a dilation and evacuation was performed the following day. The patient required two additional procedures for retained products of conception.

Discussion: Craniopagus parasiticus is an incredibly rare condition with only 9 cases reported in literature. There have been only 4 described attempts to separate craniopagus parasiticus twins with only 2 surviving the procedure. Our case presents the earliest recorded fetal MRI for craniopagus parasiticus which was then used to render a 3D model. This 3D model not only aided in discerning important anatomical structures such as umbilical cord and brain anatomy but was also used for surgical planning and patient counseling.

Conclusion: Early fetal MRI can assist with diagnostic uncertainty and can also be used to generate 3D models, which have important potential benefits for patient education and surgical planning, especially in rare medical conditions.