Diprosopus

Diprosopus, also known as craniofacial duplication or diprosopia, is an extremely rare congenital malformation characterized by the partial or complete duplication of facial structures on a single head and body. The term derives from the Greek 'di' (two) and 'prosopon' (face). It is considered the rarest form of conjoined twinning and falls within the spectrum of cephalic conjoined anomalies. The condition results from abnormal activity of the protein Sonic Hedgehog (SHH) during embryonic development, which plays a critical role in craniofacial patterning. The degree of duplication varies widely, ranging from duplication of isolated structures such as the nose or mouth to near-complete duplication of the entire face, including two complete sets of eyes, noses, and mouths on a single head. Diprosopus primarily affects the craniofacial system, but associated anomalies may involve the central nervous system (including brain malformations such as anencephaly or varying degrees of cerebral duplication), the cardiovascular system, and the gastrointestinal tract. Many affected infants also have neural tube defects. Most cases are stillborn or die shortly after birth due to the severity of the associated malformations. In rare instances where the duplication is less extensive, survival beyond the neonatal period has been reported, though this remains exceptionally uncommon. There is no established curative treatment for diprosopus. Management is largely supportive and palliative, depending on the extent of duplication and the presence of life-threatening associated anomalies. In very rare cases with limited duplication, surgical intervention may be considered, but the complexity of shared vascular and neural structures makes surgical correction extremely challenging. Prenatal diagnosis is possible through detailed ultrasonography, which can detect facial duplication during pregnancy. Genetic counseling is offered to affected families, though the condition is generally considered sporadic with no known familial recurrence pattern.

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