The paranasal sinuses are hollow, air-filled spaces located within the bones of the face and surrounding the nasal cavity, a system of air channels connecting the nose with the back of the throat.7 There are 4 paranasal sinuses, the frontal sinuses are in the lower forehead above the nose, the maxillary sinuses are in the cheekbones on either side of the nose, the ethmoid sinuses are beside the upper nose, between the eyes, and the sphenoid sinuses are behind the nose, in the center of the skull.7 (See Figure 1) Blockage of the small sinus openings from swelling, infection, allergy, and other causes can result in sinusitis, which means inflammation of the sinus cavities.11 Typically patients with a sinus problem experience one or more of the following symptoms: pain over the cheeks and upper teeth is often caused by maxillary sinus inflammation, pain in the forehead, above the eyebrow, may be caused by frontal sinus inflammation, pain around or behind the eyes is caused by ethmoid sinus inflammation, and pain behind the eyes, on top of the head, or in both temples may be caused by sphenoid sinus inflammation.4 Nasal discharge that lasts more than a week, coughing, headache, and facial pain, are the main indicators of sinusitis.4 Doctors prescribe antibiotics, decongestants, and steroids if the sinus infection fails to go away on its own. If chronic sinusitis is suspected, referral to an Ear, Nose, and Throat Specialist (ENT) is recommended, as nasal endoscopy will often identify the source of the pathology. If all fails, then a computed tomography (CT) scan is essential to determine if there is anatomic cause.
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Figure 1: Location of 4 paranasal sinuses
The osteomeatal complex is the most important sinus opening. Any process that causes blockage in this sensitive area can occlude the other sinuses that drain into the osteomeatal complex. When obstruction occurs, the mucus is retained in the sinus cavity. These stagnant secretions thicken and provide a medium for bacterial growth. Obstruction also leads to decreased oxygen levels within the sinus, which exacerbates sinus infections from both aerobic and anaerobic bacteria. These changes lead to damage to the sinus lining. The retained secretions and infection lead to further tissue inflammation, which in turn leads to further blockage. These events demonstrate a vicious cycle that leads to chronic sinusitis.11 On a CT scan it is impossible to differentiate between the common cold and bacterial sinusitis, and thus it is important that a CT scan is obtained after the patient has been maximally treated (see Figure 3 for a patient going in for a CT). 2 The need for CT in pre-operative assessment of patients prior to endoscopic sinus surgery is essential.3 It provides an accurate measurement of the paranasal sinuses and craniofascial bones (See Figure 4 for an image of a CT taken of the sinuses).9 Three millimeter section direct coronal
Figure 3: Patient having a CT
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Figure 2: Illustration of Osteomeatal Complex
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CT scanning, with the patient in the prone position and hyperextended, is currently the best preoperative evaluation for endoscopic sinus surgery.9 Particular attention should be with coronal CT scans, as the osteomeatal complex, is best seen in coronal CT scans; however, axial CT scans provide a better view of
Figure 4: Direct Coronal CT of Sinuses
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the frontal sinuses.2 Contrast- enhanced CT only needs to be used with the presence of a mass is suggested.9 Magnetic Resonance Imaging (MRI) is however, the primary choice for detecting tumors.13 The role of identifying, in CT scans, the different sinuses, along with the orbits, orbital walls, maxillary alveolus, and nasal sputum is essential.2 Anatomical variants encountered on CT scans: deviated nasal sputum, asymmetry of sinuses, including shape and size, air cells, fluid, mucosal thickening, bony fractures, cysts, and tumors is important in determining whether or not they contribute to the symptoms of the patient.2 Clouding of a single sinus is unusual, and may be due to a tumor or maxillary sinus hypoplasia. Particular attention will be paid to maxillary sinus hypoplasia because of its rarity; it only affects 2% of the population, and many radiologists and ENTs do not encounter it often, thus leading to unnecessary surgery.1,6 In order to read CT scans of the paranasal sinus it is important to become familiar with the locations of importance. The follow two figures illustrate many important features of the paransal sinuses.
Figure 5: Sagittal view of Paransal Sinuses
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Figure 6: Coronal View of Paranasal Sinuses
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LEGEND: F - Frontal sinuses, E - Ethmoid sinuses, M - Maxillary sinuses, O - Maxillary sinus ostium, SS - Sphenoid sinus ST- Superior turbinate, T - Middle turbinate, IT- Inferior turbinate, SM- Superior meatus, MM- Middle meatus, SR - Sphenoethmoidal recess, S- Septum, ET - Eustachian tube orifice, A - Adenoids
In Figure 5, the three overlapping flaps of tissue, called turbinates (inferior - IT, middle T, and superior - ST ) protect the openings of the sinuses, and allow humidification, filtration and warming of air. The frontal (F) sinus is seen in this view, but is not usually involved to any great extent in sinusitis. The sphenoid sinus (SS) is also seen and drains into the sphenoethmoidal recess (SR) In Figure 6, the maxillary sinuses (M) drain through the maxillary sinus ostia (O) into the middle meatus (MM). The opening at O appears to be extremely large; however it is the size of a pin head and actually follows a rather circuitous route. The ethmoid sinuses (E) drain into both the middle meatus as well as into the superior meatus (SM). The middle meatus (MM) is bounded by the middle turbinate (T) and the inferior turbinate (IT). The septum (S) creates a barrier between the two sides of the nose. If it is deviated to a great enough extent, an obstruction can occur. Occasionally, there may be a perforation (hole) in the septum, which can cause problems with the architectural support of the nose. 14
As in reading any CT scan, there are a few principles that must be followed. The first is looking at the name, the second is looking at the date, and the third is looking at the orientation. One must look for an R or L. There are four radiographic densities: air, fat, water, and bone. On the CT scan, bone appears white, air appears black, and soft tissue, fluid, or muscle is varying shades of gray. 14 When 2 structures of the same radiographic density are adjacent then the border between them becomes obscured. For example, pus or fluid in the sinus has the same density as thickening of the sinus mucosa.2 When looking at images, it is important to look at more than one and follow images through a systematic approach. This allows for image subtleties to not be missed.2
There are excellent papers describing a systematic approach for the interpretation of computed tomography scans. One such paper describes a six step guide.17 The first step is to orient the scan sequence from anterior to posterior. The ethmoidal bulla lies medially to the maxillary sinus and is one of the most consistent landmarks. (See Figure) The second step is to examine the lamina papyracea, uncinate process, and middle turbinate. In this step, it is important to look at the lamina papyracea and see if it dehiscent (a rupture or opening) through infection or disease (See Figure 8). After this is done one must examine the uncinate process and determine
Figure 8: A dehiscent lamina papyracea
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Figure 7: The ethmoidal bulla is a consistent 17 landmark
it’s proximity to the orbit (See Figure 8). Also it is important to locate the presence of a Haller
cell (see Figure 9) as so it is not mistaken as the antrum. Further there may be an expanded air cell known as a concha bullosa (see Figure 10) Next it is important to determine if there is maxillary sinus hypoplasia.17
Figurw 9: The uncinate process (outlined arrow)
and a Haller cell (solid arrow) 17
Figure 10: A concha bullosa
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In Figure 11 one can see that the right maxillary sinus of the patient is smaller than the left maxillary sinus. This is termed hypoplastic. Unilateral hypoplasia has been reported in 1.73% to 10.4% and bilateral hypoposlia in 7.2% of the world.16 The reasons for maxillary sinus hypoplasia are thought to involve a sinus infection during the first year of life. The importance of identifying maxillary sinus hypoplasia is due to deformities in the uncinate process which is a key landmark in endoscopic surgery. This is because the first incision during surgery is placed on or anterior to the uncinate process and thus is the first structure to be removed. If the sinus is hypoplastic it is possible the uncinate process is absent and thus the first incision during surgery could cause unforeseen orbital complications.16
Figure 11: Hypoplastic Maxillary Sinus
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Therefore, it is of vital importance to identify a hypoplastic sinus with a CT scan before surgery.
Continuing to follow the six step guide as outlined in a paper by Masen et. al, the third step is examine the area of frontal recess, which lies anterior and superior to the ethmoid infundibulum (see Figure 12). The fourth step is
to determine the height of the skull base by identifying the cribriform plate and the height of the ethmoid sinuses (fovea ethmoidalis). If there are
Figure 12: The frontal recess (outlined arrow) and 17 a paradoxical middle turbinate (solid arrow)
asymmetries it is important for the surgeon to know. The fifth step is to examine the sphenoid sinuses to determine the prescence of the cartiod artery and if an Onodi cell is present (see Figure 13). If an Onodi cell is found, there is a greater risk of possibily damaging the optic nerve during surgery. The final and sixth step is to determine if surgery
is necessary and if the pathology suggests some other medical condition. 17
Figure 13: An Onodi Cell
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Now that a systematic approach to looking at CT scans of the paranasal sinus has been developed, CT scans and observations about them will be discussed. Even so, it is important to understand that when evaluating a patient numerous scans need to be looked at and thoroughly examined. Therefore the following discussions due not truly follow the systematic approach as
previously discussed and are more intended to familiarize oneself with CT scan images of the paranasal sinuses.
The following figure represents a CT scan of a healthy sinus. (see Figure 14) It is important to note that the patient’s right side is on the left when viewing it. Of note in the bottom portion of the scan is a ray pattern emanating from the teeth. This is as a result of poor penetration
of the x-rays through the metal in the teeth. On the patient's left side at the +
Figure 14: CT scan of Healthy Patient
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sign, there is a very sharp distinct border between the black air in the maxillary sinus and the white bone. The asterisk (*) is at the point where drainage occurs from the maxillary sinus into the nose through part of the ostiomeatal unit. The maxillary sinus ostia is bounded below by the uncinate process (U) and above by the lower bony portion of the ethmoid sinuses (E). A narrowing in this area can be very critical. The ethmoid sinuses are much smaller than the maxillary sinuses. On the right side of the patient one can see the middle turbinate (MT) as well as inferior turbinate (IT). There is a slight deviation of the septum (S) to the right side, but in this particular case is not likely causing any obstruction. There is air contained in the middle turbinate on the left called the concha bullosa (C). This represents a normal anatomical variant in which the ethmoid sinuses have pushed down into the middle turbinate. In this case, it does not
appear to have caused a problem, but often it will cause a significant enlargement of the middle turbinate and consequently an obstruction on one side of the nose.14
The next figure (Figure 15) shows a patient with sinus disease. Attention should first be directed to the + sign on the left side of the patient. Compared to the previous scan, there is a significant amount of grayish thickening between the white bone and the black sinuses. Any thickening over 3 mm is definitely abnormal. Note that this
Figure 15: Patient With Sinus Disease
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thickening involves almost the entire maxillary sinus on both sides. This scan shows no opening on the right maxillary ostium now, only the gray tissue completely blocking the ostium. Not surprisingly, this patient had a great deal of pain as a result of that blockage. Although there is more thickening of the sinus lining on the right, there is more room to breathe through the nose on the right side (*) than on the left side. This is largely as a result of the deformity of the middle turbinate, located just above the asterisk (*). This may have contributed to the sinus disease in this case, causing obstruction of the ostiomeatal unit. Not surprisingly the ethmoid sinuses were involved as well. The ethmoid sinuses are either filled with polyps (P) or the lining is thickened. There is very little air left in the ethmoid sinuses (E). 14
The next figure (Figure 16) is another patient with sinus disease, but this time the patient has larger polyps or cysts (P).There is obstruction of the ostium on the right side of the patient and on the left side the ostium (O) cannot be clearly seen. The ethmoid sinuses (E) on the
Figure 16: Patient with Sinus Disease
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right side are completely obstructed, being filled with either polyps, cysts or thickening of the sinuses. On the left side, there is some thickening, but for the most part the ethmoid sinuses are fairly clear. The asterisk (*) on the left side represents the point at which the ethmoid sinuses merge into the frontal sinuses. It is important to pay attention to the differences in size between the middle turbinate (MT), and inferior turbinates (IT) on each side.14
The next figure (Figure 17) shows the patient seen in Figure 16 after surgery. The polyps that were previously in the maxillary sinus (M) are now gone and the opening at the maxillary sinus ostia (O) is wide open, having had the uncinate process removed. The ethmoid sinuses (E) on both sides have been cleaned out. The surgery which was performed did not involve extensive removal of the lining of the sinuses. Just opening them up and allowing them to "breathe" is often enough to prevent severe disease. Of note, however, is the fact that this patient still doesn't have a normal nasal airway. In addition to having sinus problems, this patient also has allergy problems which had to be treated in order to prevent future nasal problems and sinus disease.14
Figure 17: Patient After Surgery
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The above discussions of CT scans showed the patient’s paranasal sinuses as coronal CT images. Even so, axial CT scans can also show disease. For example, Figure 18 is an axial CT scan showing complete opacification of the left maxillary sinus. Axial CT scans show erosion of the posterior table of the frontal sinus, the sphenoethmoidal bony plates, basal lamella, pterygomaxillary fissure, and
Figure 18: Axial CT Scan with Complete Opacification of Left 19 Maxillary Sinus
pterygoplatine fossa better than in coronal CT scans. 9
Another important topic in the realm of the paranasal sinuses, is the close proximity of the maxillary sinuses to teeth. In some cases, patients have roots of the teeth in the maxillary sinus. Panoramic x-rays can also sometimes detect problems in the maxillary sinus (see Figure 19). This has implications for reading CT scans of the paranasal sinuses. Figure 20 shows a patient who had dental implants that penetrated into the nasal cavity and
Figure 19: Dental x-ray demonstrates a large 20 radiopaque mass in the right maxillary sinus.
maxillary sinus. Therefore, it is important to pay attention to the roots of teeth, teeth, and potential
Figure 20: Axial CT image showing implants 20 in nasal cavity and maxillary sinus.
complications that could arise from odontogenic origin. 20
If a CT scan confirms the presence of sinusitis and if patients have not responded adequately with optimal medical treatment including medications, allergy evaluation, and immunological evaluation, an ENT may recommend endoscopic sinus surgery.14 A new combination of futuristic computer technology and traditional surgery is now allowing surgeons at several leading hospitals in the United States, such as Northwestern Memorial Hospital and Thomas Jefferson University Hospital, to successfully treat chronic sinus problems less invasively than in the past.5 Image-guided surgery incorporates technology such as infrared optics, electromagnetic beams, interactive CT scans and sophisticated computers to treat
sinusitis.5 After taking a CT scan of the patient's sinuses, the surgeon can correlate the CT image with the position of a probe.5 The surgeon places a hand-held probe in the patient's nose, while correlating the probe's position with the scan on a computer screen (see Figure 21 and Figure 22).5 This imageguidance system shows the location of the probe's tip so the surgeon can safely navigate through trouble spots, which is particularly useful in patients with unusual sinus anatomy or prior surgeries.5 The precision of computerized instrument localization and navigation is critical to maneuvering safely within concealed anatomy and allows the surgeon to perform more precise and thorough surgery. Patients undergoing image-guided endoscopy have
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Figure 21: Computer Guided Sinus Surgery
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Figure 22: An image taken at the time during Computer Guided Sinus Surgery. The CT scan images represent the coronal and reconstructed sagittal and axial views. The probe is at the level 14 of the middle turbinate.
the prospect of less pain and shorter recovery time as a result of the improved technique, when compared with the conventional approach.5 Prior to the development of image guided surgery, surgeons performing minimally-invasive surgery could only see the surface area visible from the end of the endoscope. This two-dimensional approach is limited because the surgeon must correlate the patient’s medical images mentally with the operative field to determine the location of vital anatomical structures that lie beyond the view of the monocular endoscope. Image guided
Figure 23: GE InstaTrak
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surgery overcomes this limitation and provides the surgeon with realtime enhanced visualization.14 One such system currently being used is
the GE InstaTrak 3500 (see Figure 23).15
Surgery is typically done under either local or general anesthesia depending on the extent of the surgery which needs to be done, the patient involved, or the preference of the surgeon. At the time of surgery, the surgeon will initially correct a deviated septum if necessary. Depending upon circumstances, it may be occasionally necessary to slightly trim the turbinates, especially the middle turbinate to access the meatus and sinuses adequately. Most surgeons prefer to limit the amount of turbinate removal as there is some evidence that olfactory sensation may be related to tissue in the middle turbinate. Additionally, removal of large amounts of tissue may create scarring as well as an increase in nasal congestion. 14
An osteotomy is typically made at the site of the naturally occurring maxillary sinus ostium with removal of the uncinate process. If adequate removal of tissue is not made, there may not be an adequate size ostium created for drainage, and scar tissue may cause obstruction. Depending upon the patient, the ethmoid sinuses may also need to be removed. The ethmoid
sinuses are different than the maxillary and sphenoid sinuses in that they are a honeycomb, and as a result must be removed so that adequate drainage occurs without compromising vital structures. Under most circumstances the frontal sinus and sphenoid sinus need not to be entered.14
In general, most surgeons prefer to do minimal surgery and not strip the mucosa as patients generally do better in the long run. Adequate drainage is often enough such that more radical surgery does not need to be performed. The success rate and operative complications are dramatically related to the skill of the surgeon for which there is a very long, steep learning curve. Post operative care is extremely important, as patients must be diligently followed in order to prevent adhesions and other complications.14
It is important to realize that surgery does not prevent future episodes of sinusitis. The ostium is enlarged, therefore providing adequate drainage. A sinusitis is similar to an abscess and the surgery allows adequate drainage. It does not ensure that there will be no more problems with the abscess. In addition, future sinusitis can occur; however, can be more adequately treated because drainage is better.14
Patients typically are out of work for at least 1 week after surgery and typically take approximately 6 weeks to heal. It may take 6-12 months for the entire healing process to be completed. A small percentage of patients who have had surgery do not improve optimally. The reasons for this include adhesions, development of sinusitis in sinuses not previously operated upon, polyps, exposure to irritants or toxins, especially tobacco smoke, inadequate initial surgery, poor compliance with medications, inadequate treatment of allergies, immunodeficiency, and other medical problems.14
References 1. Modic, M T et al.”Maxillary Hypoplasia Visualized with Computer Tomography.” Radiology 135:383-385, May 1980. (10/18/07) 2. Staffel, J G et al. “Chapter 10: How to Read a Sinus CT Scan.” The American Academy of Otolaryngology - Head and Neck Surgery Foundation. (10/18/07) 3. Tan, How-Ming and Chong, Vincent FH. “CT of the Paranasl Sinuses: Normal Antamoy, Variants, and Pathology.” CME Radiology 2001; 2(3):120-125. (10/18/07) 4. “Sinus Infection” eMedicineHealth.com (3/22/07) (10/18/07) 5. “Surgeons at Jefferson Hospital will Explore the Sinuses on the Web and Demonstrate HighTech Procedure to Treat Chronic Sinus Problems.” Thomas Jefferson University Hospital (9/17/07) (10/18/07) 6. As stated by Robert M. Meyers, M.D. Suburban Ear, Nose, and Throat Specialist Ltd. 7. Paranasal Sinus and Nasal Cavity Cancer Treatment. National Cancer Institute. (9/20/07) (11/12/07) 8. McKesson Health Solutions. Location of Sinuses (11/12/07) 9. Mafee, M, Valvassori, G, and Becker, M. Valvassori’s Imaging of the Head and Neck. 2nd Edition. 2004 10. Radiology Info (11/12/07) 11. Becker, Daniel M.D. General Information About Sinuses and Sinusitis. (11/12/07) 12. Loma Linda University Medical Center. (11/06/04) (11/12/07) 13. Computed Tomography – Sinuses. Radiology Info. (05/23/07) (11/12/07)
14. Tichenor, Wellington M.D. Sinus CT Scans. (04/22/07) (11/12/07) 15. GE Healthcare. (11/12/07) 16. http://journals.cambridge.org/download.php?file=%2FJLO%2FJLO116_02%2FS002221510200 0397a.pdf&code=466e2b16fff2e15591f4e05f6aebbcf2 17. http://journals.cambridge.org/download.php?file=%2FJLO%2FJLO112_10%2FS002221510014 2276a.pdf&code=e6b522063c6819c65eecd461067b11c3 18. eMedicine from WebMD. Sinusitus, Maxillary, Chronic, Surgical Treatment (5/19/05) (11/12/07) 19. Medscape Today from WebMD. Fungal Sinusitus Current Trends in Diagnostics and Treatment. 2000 (11/12/07) 20. Huang, B M.D., Larheim, T, D.D.S., Westesson, P-L, M.D. PhD, D.D.S. “Maxillary Sinus Pathology of Odontogenic Origin”. Division of Diagnostic and Interventional Neuroradiology, Department of Imaging Sciences, University of Rochester Medical Center, Rochester, New York. < http://www.urmc.rochester.edu/smd/Rad/neuroimages/photos/ASHNR06_Huang.pdf> (11/12/07)