*2.1.5. Cyclopia*

**Definition:** Cyclopia is another type of anomaly, in which the fetus has only one single orbital fossa, with bulbs, eyelids and lacrimal apparatus fused to a variable degree. In many cases, there is one single eye or one partially divided eye, in a single orbit and arhinia with proboscis (**Figure 12**), [14, 15].

**Incidence:** Cyclopia results from the incomplete cleavage of the prosencephalon into right and left hemispheres, a process which should be occurring between the 18th and the 28th day of pregnancy, and it is a lethal human malformation, relatively complex, but also quite rare. Moreover, holoprosencephaly occurs in 1/16,000 live births [16].

**Figure 12.** A. Axial and sagittal scans of a fetus at 15 weeks of gestation show cyclopia and proboscis. B. Ethmocephaly— Postmortem demonstrating hypotelorism and proboscis.

**The etiology** of this rare syndrome incompatible with life is still not known in detail, because most cases are sporadic, even if the implication of heterogeneous risk factors has been proven. Among risk factors, we include maternal diabetes (the only formally recognized environmental factor, with a 1% risk and a 200-fold increase in fetal holoprosencephaly), infections during pregnancy (TORCHs), active drugs during pregnancy physical agents (ultraviolet light), and chromosomal (mostly trisomy 13) and genetic causes (familial occurrences in twins and in consanguineous marriages [17].

In order to get **the differential diagnosis** of these cases, we must distinguish between ethmocephaly and cebocephaly. In other words, we must be able to trace extreme hypotelorism, arhinia and blinded proboscis located between the eyes as opposed to hypotelorism and a single nostril nose without midline cleft. In case the image shows united palatine and lacrimal bones, as well as no sign of nasal bones, maxilla and nasal septum, then the diagnosis is ethmocephaly [15].
