• The Frontal Sinus

If you have recently consulted a Ear Nose & Throat doctor for nose and sinus related symptoms and the doctor has suggested a CT scan of your sinuses here is the reason why. Computed tomography, more commonly known as a CT or CAT scan, is a diagnostic test that produces multiple images or pictures of the inside of the body. The cross-sectional images generated during a CT scan can be reformatted in multiple planes, and can even generate three-dimensional images. Unlike the traditional X-rays which provide very little information, CT scans are preferred because of the detailed information the CT images provide. CT scans is the imaging modality of choice for evaluating the paranasal sinuses. CT of the sinuses is primarily used to detect the presence of disease which may be inflammatory, infective or a growth within the sinuses. The paranasal sinuses are hollow, air-filled spaces located within the bones of the face and surrounding the nasal cavity. These sinuses connect with the nasal cavity trough very narrow channels a system of air channels connecting the nose with the back of the throat.

Figure 1


There are four pairs of sinuses, each connected to the nasal cavity by small openings. The sinus in the forehead is the “frontal sinus” shown as FS in the Figure 1, the sinus in the cheek bone is called the “maxillary sinus” shown as MS, and multiple small sinus between the eyes and the nose are called the “ethmoid sinuses” shown as ES and the sinus located deep in the skull behind the nose and somewhere in the middle of the skull is the “Sphenoid Sinus” shown as Ss in the figure 1. On the CT scan “air” appears black and the “bone” white on the images. This provides an excellent contrast which enables detection of any disease with in the sinuses. The white arrow shows the contents of the right eye are proplapsing into the right ethmoid sinus. The information is critical to the surgeon so that he can take precautionary measure to avoid a major complication to the eye. Similarly in  figure 4B the white arrow is pointing to the optic nerve which is the nerve of vision. Notice that the nerve is literally floating in the sinus. Without the CT scan the surgeon would be completely oblivious to this situation. Damage to nerve may render the patient blind.   CT scans also provide information that enables us to differentiate whether the sinuses are full of inflammatory disease, fungus, fluid, mucoid secretions or tumors. Sometimes contrast material may be used for this purpose.

Figure 2.


In the event there is any inflammation of the mucosal lining, the mucosa becomes swollen and will appear as thickened “grey” lining as shown in figure 2A (white arrow). If the disease is quite extensive the entire sinus becomes “grey”. (Figure 2B: Note the left maxillary sinus is completely greyed out. This may be due to inflammation, infection, pus, fungus or evena growth with in the sinus.


Figure 3



As just one, few or all the sinuses may be involved with the disease process, CT scans of the sinuses will also provide information on the extent of the disease. This information is crucial in planning the surgery.In figure 3 all the sinuses are involved in the disease process.


Figure 4


The CT scan is also akin to a “road map.” It provides information of the pertinent anatomy of the sinuses. Anatomy of the sinuses is not fixed. It varies from person to person. In fact, it can be vary on different sides of the same person. This information is important to avoid some critical structures such as the orbit, brain, optic nerves and major blood vessels during the surgery.In figure 4A the contents of the right eye are prolapsing into the ethmoid sinuses because of a “dehiscence” of a bony defect in the partition between the two. This condition if not recognised before the surgery predisposes the eye contents to injury during the surgery. The injury can be serious enough to result in blindness. In figure 4B the arrow points to the right optic nerve which is literally “floating” in the right side of the sphenoid sinus. Again if not recognosed before the surgery the nerve could be damaged during the surgery resulting in blindness.

I am sure by now you will understand of the importance of CT scan particularly when surgery is contemplated. It is to “get to know your sinuses better!!”