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Flat nasal bridge (also known as depressed nasal bridge) refers to reduced prominence or underdevelopment of the nasal bones and midface, resulting in a flattened appearance of the nose, particularly in profile.

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It can be a normal variant in some populations or a clinical feature of genetic, syndromic, or skeletal disorders, especially those affecting midfacial development.

Anatomical basis

Structure	Contribution
Nasal bones	Provide the bony dorsum of the nose
Nasal cartilage	Contributes to tip and alae; not involved in the bridge
Midface development	Involves the maxilla and frontal processes; key in syndromic causes

Clinical Significance

Flat nasal bridge can be:

Isolated (e.g. familial trait, especially in some ethnicities)
Associated with syndromes: Indicative of underlying skeletal dysplasia or midfacial hypoplasia

A. Genetic Syndromes

Syndrome	Key Features
Down syndrome (Trisomy 21)	Brachycephaly, epicanthal folds, single palmar crease
Trisomy 13 (Patau)	Cleft lip/palate, polydactyly, holoprosencephaly
Trisomy 18 (Edwards)	Micrognathia, clenched hands, rocker-bottom feet
Williams syndrome	Elfin facies, supravalvular aortic stenosis, hypercalcemia
‣	Hypertelorism, short stature, congenital heart disease
Cri-du-chat syndrome	Microcephaly, high-pitched cry, ID
‣	Smooth philtrum, thin upper lip, short palpebral fissures

B. Skeletal Dysplasias and Bone Disorders

Disorder	Features
Achondroplasia	Midface hypoplasia, rhizomelic limb shortening
Hypochondroplasia	Milder than achondroplasia; flat nasal bridge can occur
Thanatophoric dysplasia	Lethal skeletal dysplasia, depressed nasal bridge
Cleidocranial dysplasia	Midface hypoplasia, open sutures, absent clavicles
Mucopolysaccharidoses (e.g., Hurler syndrome)	Coarse facial features, macrocephaly, corneal clouding

C. Infectious and Environmental

Cause	Notes
Congenital syphilis	Saddle nose (destruction of nasal cartilage)
Fetal alcohol spectrum disorder (FASD)	Includes midface hypoplasia with nasal flattening
Congenital Zika syndrome	Microcephaly, midface hypoplasia, calcifications

Radiology

A. Fetal Ultrasound (2nd–3rd trimester)

Measurement	Significance
Nasal bone length (NBL)	Short or absent NBL suggests aneuploidy (especially Trisomy 21)
Profile view	Helps assess nasal bridge contour and midface hypoplasia
Hypoplastic nasal bone	Soft marker for Down syndrome

B. Postnatal Imaging (X-ray / CT / 3D imaging)