HEAD A N D NECK
Radiology of the bony orbit
THE NASAL CAVITY AND PARANASAL SINUSES (Figs 1. 8, 1. 11 and 1. 12)
Plain films
The nasal cavity is a passage from the external nose anteriorly to the nasopharynx posteriorly. The frontal, ethmoid, sphenoid and maxillary sinuses form the paired paranasal sinuses and are situated around, and drain into,
The orbits may be assessed on OF20 and OM projections (see Figs 1. 4 and 1. 8). Asymmetry between the superior orbital fissures is common. The fissure separates the greater wing of sphenoid (below) from the lesser wing (above). A straight line is seen running through the orbit from the superolateral part of the rim inferiorly and medially. This is caused by the X-ray beam hitting the curving greater wing of sphenoid at a tangent, and is known as the innominate line. Owing to its oblique course through the skull base, a specially angulated radiographic projection is required to demonstrate each optic foramen. The normal optic foramen is less than 7 mm in diameter. The dimensions of the foramen should not vary by more than 1 mm. There may, however, be a separate opening for the ophthalmic artery below the foramen, or the foramen may have a keyhole configuration if the foramina are not completely separate. The optic canal is related to the sphenoid sinus and an axial view of this is part of assessment for sinus surgery. The floor of the orbit and the infraorbital canal are best seen on the OM (see Fig. 1. 8) and OM30 projections. Computed tomography The bony orbit and its soft-tissue contents are demonstrated very well by CT (see Fig. 1. 29). Axial or coronal images may be obtained. Coronal imaging shows the floor of the orbit and is useful for the assessment of trauma where a fracture is suspected. MRI is more valuable for demonstration of the soft-tissue contents of the orbit than the bone.
1. 2. 3. 4. 5. G. 7.
Nasal septum Maxillary sinus Middle nasal turbinate Inferior nasal turbinate Superior meatus Middle meatus Inferior meatus
8. 9. 10. 11. 12. 13.
Ethmoid infundibulum Uncinate process Maxillary ostium Maxillary infundibulum Infraorbital nerve Alveolar process of maxilla
11
