SKULL SHAPE IN TRISOMY 18

1. Normal Shaped Skull
• Normal occiput due to the higher frequency of posterior fossa cysts.
• Less pointing of the frontal bones due to a lesser degree of facial hypoplasia.
2. Dolicocephaly
• Decreased cephalic index.
• Due to the severe oligohydramnios and lateral skull compression that may accompany the IUGR.
3. Strawberry Skull
• Brachycephaly with an increased cephalic index.
• Flattening of the occiput (due to hypoplasia of the occipital lobes, brainstem and cerebellum).
• Pointing of the frontal bones (distinguish from scalloping). Thought to be due to a vascular abnormality affecting the 1st and 2nd branchial arches.
• Hypoplasia of face including facial artery muscles, maxilla, mandible, frontal and temporal bones.
• Micropthalmia with narrow nasal bridge and palate.
• Absent or rudimentary parotid and submandibular glands.
• Hypoplasia of frontal lobes of brain.

REFERENCES

1. Nicolaides KH, Salvesen DR, Snijders RJM, Gosden CM. Strawberry-Shaped Skull in Fetal Trisomy 18. Fetal Diagn Ther 1992,7:132-137.