Head and Neck Imaging

Sinonasal cavities, anatomical variations

The sinonasal cavities are an anatomically complex region; drainage of secretions from the sinusal cavities has to occur through narrow spaces (see ostiomeatal unit; sphenoethmoid recess). For basal anatomy, see face.

Many anatomical variations are possible; they can be classified according to the structures involved or the type of alteration (Table 1).

There is currently little epidemiologic evidence that anatomical variations are the primary cause of sinusitis. However, it is better established that these variations do contribute to the pathophysiology and the persistence of inflammation. An exact knowledge of these anatomical variations is a prerequisite for functional functional endoscopic sinus surgery. For example, knowledge of the relationship of the cribriform plate to the ethmoid roof (see Keros classification) and of the presence of eventual dehiscencies of the carotid artery canal, optic nerve canal and lamina papyracea (see bony dehiscence), is essential to prevent and avoid complication during surgery.

Sinonasal cavities, anatomical variations, Table 1. (Adapted from: Jorissen M., Hermans R., Bertrand B., Eloy Ph.: Anatomical variations and sinusitis. Acta oto-rhino-laryngologica belg. 1997, 51: 219-226).

Bony structure displacementPneumatizationOpenings
septal deviationconcha bullosaperforation of the uncinate process
paradoxically curved middle turbinateHaller's cellsupplementary ostium in maxillary sinus
deflected uncinate processagger nasi cell
uncinate process
enlarged ethmoidal bulla
frontal cell and supraorbital cell

Nasal septum deviation

In patients over the age of 14 years, approximately 70% of nasal septa are deviated (Fig.1) (Fig.2). The deviation can be classified according to the severity into three grades:

- grade I: any septal deviation, that does not contact the lateral nasal wall structures

- grade II: contact with lateral nasal wall structures, but no contact after topical decongestion

- grade III: contact with lateral nasal wall structures, that persists after decongestion

Only grades II/III correlate with nasal and sinus pathology. Nasal septum deviation may cause obstruction at the ostiomeatal unit. Inflammation in the contralateral maxillary and ethmoidal sinuses has been noted, which may be related to air turbulence causing increased mucosal drying and increased particle deposition.

Middle turbinate

  • concha bullosa: pneumatization of the middle turbinate. A distinction is made between a true concha bullosa (Figs. 1, 2) and an interlamellar cell (see concha bullosa (VI:2), Fig. 1 and concha bullosa (VI:2), Fig. 2). Only the true concha bullosa is associated with sinusitis. A unilateral concha bullosa is often associated with a contralateral septal deviation.

  • paradoxically curved middle turbinate, showing a concavity towards the septum. It does not predispose to sinusitis, but may interfere with an endoscopic surgical procedure.

    Uncinate process

    • deflected uncinate process, either laterally or medially (Fig. 2). A laterally deflected uncinate process may narrow the ethmoid infundibulum.
    • uncinate process perforation: opening between nasal cavity and ethmoid infundibulum. Probably to be regarded as a sequela of sinusitis.
    • pneumatized uncinate process (Fig. 3): infrequently seen, occurs mostly in the superior part. There is no evidence for an association with sinusitis.

    Ethmoid bulla

    An enlarged ethmoid bulla may prolapse into the ostiomeatal unit, but there is no evidence that this is more frequently found in patients with sinusitis than in controls (Fig. 1).
     
    Haller's cell

    Ethmoid extensions within the maxillary sinus, along the floor of the orbit (Fig. 1, Fig. 3). Their prevalence varies from 5 to 45%. Their role in sinusitis is not clear; very large Haller's cells could predispose to sinusitis.
     
    Agger nasi cell

    Most anterior ethmoidal cell. They are found in about 15% of the population; there is no evidence that they are associated with an increased incidence of sinusitis (Fig. 4).

    Supplementary ostium in the maxillary sinus

    Secondary opening between the maxillary sinus and the middle nasal meatus, most often found in the posterior nasal fontanelle; it is found in about 1830% of individuals. As it usually lies behind and below the natural ostium of the maxillary sinus, it may predispose to sinusitis by recirculation ('recycling') of infected secretions from the nose back to the maxillary sinus (Fig.5).

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    Fig.2

    Coronal CT image. Septal deviation to the right with bilateral concha bullosa media (indicated with b on left) and bilateral recurved uncinate process (arrows).
    Sinonasal cavities, anatomical variations, Fig.1
    Sinonasal cavities, anatomical variations, Fig.2
    Sinonasal cavities, anatomical variations, Fig.3
    Sinonasal cavities, anatomical variations, Fig.4
    Sinonasal cavities, anatomical variations, Fig.5