Prevalence:

• 1 in 10,000 births.

Ultrasound diagnosis:

• There is a spectrum of midline abnormalities of the nose in association with holoprosencephaly, including: arhinia (complete absence of the nasal structures), proboscis (soft tissue appendage projecting from just below the forehead) and single nostril (usually central).

Associated abnormalities:

• Chromosomal abnormalities, mainly trisomy 13, are found in 40% of cases.
• Holoprosencephaly in all cases. Genetic syndromes are found in 20% of cases.

Investigations:

• Detailed ultrasound examination, including neurosonography.
• Invasive testing for karyotyping and array.

Follow-up:

• If pregnancy continues, follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Very poor due to the associated holoprosencephaly and chromosomal abnormalities.

Recurrence:

• Isolated: 6%
• Part of trisomy 13: 1%
• Part of genetic syndromes: 25% to 50%.