Diprosopus, representing less than 1% of conjoined twinning, spans a wide spectrum of anomalies that range from minimal facial structure duplication to complete dicephalus [1
]. A commonly cited proposed aetiology of the diprosopus phenotype is rostral bifurcation or forking of the notochord, which delineates the embryonic axis and induces neurulation. This incomplete division is thought to occur somewhere between 2 and 3 weeks following fertilisation and results in two adjacent vertebral axes, neural plates and neural crest derivatives [1
]. Diprosopus is found primarily in single pregnancies, but also can be seen in dichorionic twin gestations with a normal co-twin [2
], then representing a triplet monochorionic/dichorionic pregnancy with an incomplete separation of monozygotic twins. Tetraophthalmus, referring to four eyes, can range from four fully separate globes and bony orbits, to two separate globes laterally with partial or full midline orbital fusion [2
], as in this patient. Duplication of the eyes is always associated with duplication of the nose, but nasal duplication can be isolated [4
Chromosomal anomalies have not specifically been identified in diprosopus [2
]. As such, there is no reported increased risk of recurrence. However, some authors suggest a multifactorial pathogenesis caused by interaction between environmental and genetic factors [5
Severe abnormalities associated with diprosopus have been described in the central nervous, cardiovascular, gastrointestinal and respiratory systems, and most neonates are stillborn [4
]. The more extensive duplications are associated with more severe central nervous system anomalies. Brain abnormalities include complete or partial duplication of the cerebral hemispheres with varying degrees of fusion of the posterior fossa structures [5
Imaging of diprosopus includes two- and three-dimensional sonography performed pre-natally to show the features of facial duplication [2
]. Polyhydramnios is a frequent finding [3
], presumably as a result of impaired swallowing of the amniotic fluid. MRI and CT have been used to evaluate the cranial abnormalities following birth and in post-mortem particularly if an autopsy is refused [4
]. To our knowledge, pre-natal MRI has not yet been described, and description on CT imaging has been limited to the cranium and its contents [3
Like the central nervous system anomalies, malformation of the vertebral column can be varied. Although bone sampling is included in paediatric autopsies, detailed osseous dissection is not routinely performed. Additional prosectioning of bone is usually directed by radiological findings [10
], and in our case was replaced by the CT evaluation. The full extent of the anomalies and detailed anatomy of the vertebral column duplication was readily identified with the axial CT images and subsequent reformations.
CT is occasionally used as an adjunction to, or in some cases a substitute for, conventional autopsy [11
]. The image acquisition is rapid and restraint and sedation is irrelevant [12
]. CT has been cited as an invaluable tool particularly in the area of forensic pathology [11
] and specifically in suspected cases of child abuse [11
]. In our case of congenital malformation, the bone images were important to allow a more directed autopsy. Also, the surface-rendered three-dimensional reconstructions served as a guide for the radiologist who interpreted the cranial findings but who had not seen the patient at the time of imaging. Findings such as the cleft lips were evident on the surface-rendered views and the orientation of the anatomy was easier to understand.
In this case, there were several non-osseous anomalies that were not identified or were less well defined with the CT examination. The lack of intravenous and gastrointestinal contrast and extensive lung atelectasis precluded identification of various visceral and cardiac abnormalities. The central nervous system structures, owing to inherent lack of contrast, were less well seen, although severe anomalies were identified. Therefore, CT should be considered a complementary tool that can potentially limit the extent of, rather than substitute for, autopsy.