Frontal bone

Os frontale

The single bone of the forehead that forms the anterior cranial vault, the roofs of the orbits and most of the floor of the anterior cranial fossa. It contains the frontal sinuses.

Overview

The frontal bone has a vertical squamous part (forehead), paired horizontal orbital parts (orbital plates) forming the roofs of the orbits and floor of the anterior cranial fossa, and a small nasal part articulating with the nasal bones and maxillae. Between the orbital plates lies the ethmoidal notch, filled by the cribriform plate of the ethmoid.

Externally it shows the frontal tubers (eminences), the superciliary arches above the orbits (more prominent in males), the smooth glabella between them, the supraorbital margins each pierced by a supraorbital notch or foramen (supraorbital nerve and vessels), and the zygomatic processes that meet the zygomatic bones at the frontozygomatic sutures. Internally, the frontal crest in the midline gives attachment to the falx cerebri, ending at the foramen caecum; the orbital plates bear impressions of the frontal lobe gyri.

The frontal sinuses — usually asymmetric, with a septum — lie behind the superciliary arches and drain via the frontonasal duct into the middle meatus (semilunar hiatus/frontal recess). They are rudimentary at birth, become radiographically visible at ≈7 years and reach adult size after puberty.

Location

Forehead and anterior part of the cranial vault and base.

Parts & subdivisions

Squamous part

Curved plate of the forehead with frontal tubers and superciliary arches.

Orbital parts

Thin plates forming the roofs of the orbits and floor of the anterior cranial fossa.

Nasal part

Projects down between the orbits to meet the nasal bones; nasal spine supports the bridge of the nose.

Supraorbital notch/foramen

Transmits the supraorbital nerve (V1) and vessels; pressure point for assessing painful stimulus response.

Glabella

Smooth midline prominence between the superciliary arches.

Frontal sinuses

Paired air spaces draining into the middle meatus.

Frontal crest and foramen caecum

Internal midline ridge for the falx cerebri; the foramen caecum transmits an emissary vein in the fetus.

Lacrimal fossa

Depression in the superolateral orbital roof for the lacrimal gland.

Trochlear fovea

Small pit in the superomedial orbit for the cartilaginous trochlea of superior oblique.

Anatomy

Articulations

Parietal bones (coronal suture), sphenoid, ethmoid, nasal bones, maxillae, lacrimal bones and zygomatic bones (12 bones in total).

Ossification

Intramembranous, from two primary centres (one per half) appearing ≈week 8; the halves are joined by the metopic (frontal) suture, which fuses between ≈3 and 9 months but persists in ≈5–10% of adults.

Clinical significance

Frontal sinusitis and Pott puffy tumour

Frontal sinus infection can spread to cause osteomyelitis of the frontal bone with a subperiosteal abscess (Pott puffy tumour) or intracranial abscess.

Metopic synostosis

Premature fusion of the metopic suture produces a triangular forehead (trigonocephaly) with hypotelorism.