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Portrait of Paranasal sinuses

Anatomy · Head, neck & teeth

Paranasal sinuses

Four pairs of air-filled spaces in the skull around the nose

Skull · around the nasal cavity

Air-filled cavities in the bones of the face and skull that open into the nasal cavity and are lined with the same ciliated respiratory mucosa. There are four pairs, named after the bones that contain them: the maxillary, frontal, ethmoidal and sphenoidal sinuses. They lighten the skull, add resonance to the voice and warm and moisten inhaled air, and their drainage through small openings makes them prone to infection.

How to spot them

  • ▸Four pairs: maxillary (in the cheek bones), frontal (above the eyes), ethmoidal (between the eyes) and sphenoidal (behind the nose)
  • ▸All drain into the nose, mostly into the middle meatus, through tiny openings
  • ▸Lined with ciliated mucous membrane that sweeps mucus towards their openings
  • ▸Small or absent at birth, and enlarge through childhood and adolescence

What to know

The largest of the group, sitting in the cheek bone, whose opening high on its inner wall drains poorly under gravity

The maxillary sinus (antrum of Highmore), draining into the middle meatus

Named after a seventeenth-century English physician who described the largest one in 1651 (1651)

The antrum of Highmore, after Nathaniel Highmore

The floor of the biggest is only a thin layer above the roots of the upper molars, so an extraction can leave a passage into the mouth

Oroantral fistula after upper molar extraction — the maxillary sinus

A group of small, honeycombed air cells in a bone between the nose and the eye, separated from the eye socket only by a paper-thin plate

The ethmoidal air cells and the lamina papyracea — infection can spread to the orbit

The one that sits in the body of the bone at the skull base, in front of the pituitary gland, the route for surgery on that gland

The sphenoidal sinus and transsphenoidal pituitary surgery

A pair above the eyebrows that is absent at birth and only visible on an X-ray from about six or seven years

The frontal sinuses, which drain by the frontonasal duct

Inflammation of these spaces after a cold causes facial pain that is worse on bending forward, and thick nasal discharge

Sinusitis — inflammation of the paranasal sinuses

Key ideas

  • Their drainage depends on tiny openings that lie in the middle meatus, the ostiomeatal complex. Swelling there blocks the flow and traps mucus, producing sinusitis.
  • The maxillary opening lies near the top of the cavity, so it drains against gravity and relies on the cilia to sweep mucus upwards.

Quick-fire facts

  • •Four pairs: maxillary, frontal, ethmoidal (anterior, middle and posterior air cells) and sphenoidal
  • •The maxillary sinus is the largest, with a volume of roughly 15 mL in adults
  • •Only the maxillary and ethmoid sinuses are present, small, at birth; the sphenoid develops in early childhood and the frontal from about the age of two, reaching a visible size by about 6–7 years
  • •Maxillary, anterior ethmoid and frontal sinuses drain into the middle meatus; the sphenoid drains into the sphenoethmoidal recess above the superior concha
  • •Nerve supply is by the ophthalmic (frontal, ethmoid, sphenoid) and maxillary (maxillary sinus) divisions of the trigeminal nerve, which explains why sinus pain is felt in the forehead, cheek and upper teeth
  • •The sphenoid sinus lies below the pituitary fossa and next to the cavernous sinus, carotid artery and optic nerve
  • •Nathaniel Highmore described the maxillary antrum in his 1651 book on anatomy
  • •Most sinusitis after a cold is viral and usually clears up on its own within about 4 weeks (NHS)

Drill it — 7 cards

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Sources