|
 
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| REVIEW ARTICLE |
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| Year : 2017 | Volume
: 3
| Issue : 1 | Page : 9-15 |
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Sinus radiography for sinusitis: “Why” and if considering it then “how”?
Ujwala R Newadkar
Department of Oral Medicine and Radiology, ACPM Dental College, Dhule, Maharashtra, India
| Date of Submission | 22-Apr-2017 |
| Date of Acceptance | 19-May-2017 |
| Date of Web Publication | 12-Jul-2017 |
Correspondence Address:
Ujwala R Newadkar
Department of Oral Medicine and Radiology, ACPM Dental College, Dhule - 424 003, Maharashtra
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jcrsm.jcrsm_13_17
Sinonasal imaging is performed in two major clinical scenarios: inflammatory rhinosinusitis or a suspected mass lesion. The diagnosis of rhinosinusitis is based on clinical grounds. Radiological diagnosis forms an important tool in the armamentarium to diagnose and classify rhinosinusitis. Computed tomography (CT) scan, as well as magnetic resonance imaging, may at times complement each other, to aid the clinician arrive at a diagnosis. CT scans are the gold standard study guiding management of sinusitis because they accurately depict the sinus anatomy, including soft tissue changes, anatomic variations; the osteomeatal complex, and complications, especially those involving the orbit or intracranial structures. Nevertheless, despite the best radiologic modalities, a clinicoradiological correlation is a must to accurately diagnose this often deceptive condition called rhinosinusitis. Keywords: Caldwell view, cone-beam computed tomography, paranasal sinuses, rhinosinusitis, sinus radiography
How to cite this article:
Newadkar UR. Sinus radiography for sinusitis: “Why” and if considering it then “how”?. J Curr Res Sci Med 2017;3:9-15 |
| Introduction | |  |
Sinusitis is defined as an inflammation of the epithelial lining of the paranasal sinuses. The inflammation of these tissues causes mucosal edema and an increase in mucosal secretions. The most common trigger is an acute upper respiratory infection although other causes (such as exacerbations of allergic rhinitis, dental infections or manipulations, and direct trauma) can be implicated. If blockage of sinus drainage occurs, retained secretions can promote bacterial growth and subsequent acute bacterial sinusitis. Chronic sinusitis is also very common.[1]
| Classification | | |
Although not universally accepted, a classification is commonly used to divide sinusitis into three subtypes, based on the length of time the disease has been present. Acute sinusitis refers to conditions present for <2 weeks; subacute sinusitis, to those present from 2 weeks to 3 months; and chronic sinusitis, to conditions that have been present for more than 3 months.[2] The term pansinusitis describes sinusitis affecting all the paranasal sinuses. In children, pansinusitis may suggest the possibility of cystic fibrosis.[3]
| Epidemiology | | |
Sinusitis is a highly prevalent disease, affecting 33 million Americans.[4] The Centers for Disease Control and Prevention reported that chronic sinusitis is the most common chronic condition in people younger than 45 years and, after hypertension, the second most common in people between 45 and 65 years. The prevalence of sinusitis among children is even higher than adults and may be as high as 32% in young children.[5],[6],[7] Men and women are equally affected. Sinusitis is more common in the Midwest and the southern regions of the United States than at the coasts.
| Diagnosis | | |
The diagnosis of acute sinusitis is made on the basis of history and physical examination. In 1997 the task force for rhinosinusitis developed major and minor symptomatic criteria for diagnosing rhinosinusitis [8] [Table 1]. Major criteria include nasal discharge, nasal obstruction, facial pain or pressure, postnasal drip, and olfactory dysfunction. Minor criteria include fever, cough, fatigue, dental pain, and ear fullness or pressure. Clinical judgment combined with history and physical examination is usually sufficient to diagnose sinusitis in most cases of uncomplicated acute and subacute rhinosinusitis. Imaging studies should be reserved for patients who develop recurrent acute sinusitis, complicated sinusitis or chronic sinusitis with atypical symptoms, or for defining sinus anatomy before surgery.[9],[10],[11] As previously noted, radiologic evaluations might be helpful in certain situations. Patients with the recurrent disease need to be evaluated for underlying factors that can predispose to sinusitis. Allergy evaluation for allergic rhinitis is often helpful. Other predisposing factors such as tobacco smoke exposure, immunodeficiency, and septal deviation should be considered.[12],[13] | Table 1: Diagnostic tests for chronic rhinosinusitis and recurrent acute rhinosinusitis
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Computed tomography (CT) usually aids the diagnosis of chronic sinusitis. Evaluation of the osteomeatal complex (OMC) is crucial in the management of these patients. In addition, rhinoscopy may be helpful for direct visualization of sinus ostia. Clinical evaluation combined with nasal endoscopy may obviate the need for CT imaging in some cases of chronic rhinosinusitis.[14]
| Imaging Modalities | | |
The intraoral periapical radiograph provides the most detailed, if limited view of the floor of the maxillary antrum. If during this examination, the dental practitioner suspects an abnormality, the maxillary lateral occlusal projection may be used for a more extensive view of the antrum. The panoramic radiograph depicts maxillary sinuses, revealing greater internal structure and parts of the inferior, posterior, and anteromedial walls. It is difficult to compare the internal radiopacities of the right and left sinus in the panoramic image because of variations that result from overlapping phantom images of other structures. Specialized skull views are the next step in the investigation. The standard series of plain film views of the sinuses include the occipitomental (Waters), lateral, submentovertex and Caldwell (150 PA) skull views.[15] The Waters' projection is optimal for visualization of the maxillary sinuses, especially to compare internal radiopacities, as well as the frontal sinuses and ethmoid air cells. If the Waters view is taken with the mouth open, the sphenoid sinuses may also be visualized. The submentovertex view may be useful in evaluating the lateral and posterior borders of the maxillary sinuses, as well as the ethmoid air cells. The Caldwell view is most useful in evaluating the frontal sinuses and ethmoid air cells. The lateral skull view allows examination of all four pairs of the paranasal sinuses but with each member of a pair superimposed on the other. CT and magnetic resonance imaging (MRI) have become increasingly important for the evaluation of sinus disease and have virtually replaced conventional tomography for investigations of these structures. Because CT and MRI provide multiple sections through the sinuses in different planes, they may contribute significantly to delineating the extent of disease and the final diagnosis. High-resolution axial and coronal CT and MRI examinations are the most revealing, noninvasive techniques for the paranasal sinuses and adjacent structures and areas. CT examination is appropriate to determine the extent of disease in patients who have chronic or recurrent sinusitis and considered as “gold standard.”[16] Indeed coronal CT provides superior visualization of the OMC (the region of the ostium of the maxillary sinus and the ethmoidal ostium) and nasal cavities, as well as for demonstrating any reaction in the surrounding bone to sinus disease. There is a significant radiation dose involved with CT of the sinuses, particularly to the lens. Therefore, if sinusitis can be diagnosed on clinical grounds, which it generally can, CT should be avoided unless there is concern about complications of sinusitis.[17],[18] In cases of complications of sinusitis, IV contrast is typically necessary to evaluate for ascending infection causing an intracranial epidural abscess.[19] In the postoperative patient, it may be difficult to differentiate surgical changes from recurrent sinusitis. Comparison studies are highly useful in the interpretation of the postoperative sinus as it allows for more accurate depiction of residual/recurrent disease as opposed to postoperative change. MRI provides superior visualization of the soft tissues, especially the extension of infiltrating neoplasms into the sinuses or surrounding soft tissues, or the differentiation of retained fluid secretions from soft tissue masses in the sinuses. Because of its cost, longer imaging time, and lack of bone detail, it has not been considered the imaging method of choice for routine sinus imaging. Recent public health concerns regarding the dramatic and ever-increasing usage of CT imaging and emphasis on reducing medical radiation exposure may lead to consideration of alternative imaging techniques. One study suggests that MRI-based Lund-Mackay scores did not show a statistically significant difference compared to CT-based scores in the same patients.[20] In recent years, the use of cone-beam CT has expanded from dental applications to in-office use for sinonasal evaluation. This technique offers advantages of patient convenience and likely some radiation dose reduction, though the true dose reduction in clinical use may be variable. The potential for overuse when scanning is available as an in-office procedure is significant. Strict guidelines for appropriate use should be established by practices offering this technology to avoid unnecessary scans.[21],[22],[23] Single-photon-emission computed tomography (SPECT) may have a limited role in the evaluation of chronic rhinosinusitis. One study has shown that positive SPECT in patients with chronic rhinosinusitis is correlated with poor subjective response to medical treatment.[24]
| Role of Radiologist | | |
In reporting paranasal sinus imaging, the radiologist must be aware of normal physiological changes in order not to “over report” the normal findings as inflammatory changes. An example is the nasal cycle first described by Kayser in 1889. The nasal cycle is a cyclical swelling of the ipsilateral turbinates and nasal mucosa. Unilateral enlarged turbinates are therefore a normal imaging finding.[25] Furthermore, the ethmoid mucosal linings are influenced by the nasal cycle, hence, mucosal thickening of 2 mm is commonly seen due to the nasal cycle and must not be reported as abnormal. Concerning the frontal and sphenoid sinuses, the mucosal linings should not be visualized at CT, while maxillary sinus mucosal thickening up to 4 mm is often seen in healthy individuals and considered as a normal finding.[26] With age, the nasal cycles become less prominent.
The nasal cycle, paranasal mucosa, and mucous/serous production are regulated by the autonomic nervous system and neuropeptides from the primary sensory neurons. The complex system is still not completely understood, however, it is known that the parasympathetic system and sympathetic ß-receptors stimulate secretion.[27],[28]
Primary sensory neurons releasing neurotransmittors can also cause increased mucosal swelling and fluid production. Finally, drugs that have a vasoactive effect can increase the thickness of mucosal lining and increase the serous fluid production.[29] Fluid filled sinuses can, therefore, be an incidental finding, especially in bedridden patients, and must be interpreted with care.[27],[28] Air-fluid level is frequently seen in healthy controls and is not equivalent to rhinosinusitis. Only if the patient has symptoms of rhinosinusitis and the fluid contains air bubbles, the findings can be interpreted as acute rhinosinusitis. The surrounding bone is a clue to diagnose chronic rhinosinusitis.
| Applied Diagnostic Imaging | | |
Five inflammatory patterns at CT have been described in chronic rhinosinusitis.[30] These patterns are: (1) infundibular, (2) OMC, (3) sphenoethmoid recess (SER), (4) polyposis, and (5) sporadic. The first three inflammatory patterns are caused by obstruction of mucociliary drainage routes.
- The first pattern is caused by obstruction at the level of the ethmoid infundibulum, which is the drainage route of the maxillary sinus, and hence called infundibular inflammatory pattern. In this pattern, only the ipsilateral maxillary sinus is involved
- The second pattern is caused by obstruction of the middle meatus, which is the final mucociliary drainage route of the ipsilateral maxillary, anterior ethmoid, and frontal sinuses. This pattern is referred to as the OMC (derived from ostium and meatus) inflammatory pattern. The frontal sinus drains either through the frontal recess directly to the middle meatus or through the antero-superior aspect of the ethmoid infundibulum. Isolated frontal sinusitis is regarded as a variant of OMC inflammatory pattern
- The third pattern is caused by obstruction of the SER, which is the drainage route of both the sphenoid and ipsilateral posterior ethmoid sinuses. An obstruction can proceed to rhinosinusitis only of the sphenoid sinus or also the ipsilateral posterior ethmoid sinus
- The fourth pattern is bilateral sinonasal polyposis and is characterized by enlargement of the ethmoid infundibulum as well as bulging and remodeling of the ethmoid sinus cells. In addition, the nasal cavities are filled with polyps, recognized by its downward convexity contour
- The last and fifth pattern includes all opacities that do not fit into the four previous patterns, for example, solitary polyps, retentions cysts, mucosal thickening, and postoperative mucosal thickening and therefore is referred to as the sporadic pattern.
It is important to recognize these inflammatory patterns to plan whether the patient will benefit from functional endoscopic sinus surgery (FESS), and if so the region and extent of the FESS procedure. For example, in the infundibular pattern, an uncinectomy or middle meatal antrostomy alone will open the natural maxillary sinus ostium, while in the OMC pattern more extensive surgery including both middle meatal antrostomy and anterior ethmoidectomy may be needed.[31]
| Imaging for Acute Bacterial Sinusitis | | |
The imaging hallmarks of Acute Bacterial Sinusitis (ABS) are the presence of air-fluid level (particularly unilateral) and severe opacification of a sinus. A mild mucosal thickening (<4 mm) without fluid level is a nonspecific CT finding that is frequently seen in asymptomatic subjects who undergo head CT or orbital CT for other medical complaints, as well as in patients with a common cold (upper respiratory viral infection), allergy, or asthma.[32] There is no microbiologic proof that those patients with only mucosal thickening do not have ABS since sinus puncture is not justified for patients without a fluid level in the sinus.
It is important for radiologists not to overdiagnose acute sinusitis for patients with mucosal thickening only since such a CT report contributes to overuse of antibiotic treatment for patients presenting with sinusitis symptoms. The term sinusitis means to some primary care physicians acute bacterial infection of the sinus.
| Atrophic Rhinosinusitis | | |
In atrophic rhinosinusitis, the respiratory epithelium covering the nasal and paranasal surface is replaced by nonciliated epithelium. The primary form presents with a foul smelling nasal discharge due to Klebsiella ozaenae and widened nasal passages with a paradoxical feeling of nasal congestion. It is most common in young adults from developing countries as Southern Saudi Arabia, China, Africa, India, Mediterranean and Philippines. The secondary form is the most frequent and associated with previous nasal injury, surgery, or inflammation.[33] Atrophic rhinitis has become a more common form of chronic rhinosinusitis. However, due to lack of clinical criteria, the condition is under-diagnosed.[34] It has been suggested that the secondary form is a final common pathway following injury of the nasal mucosa. Only a few papers describe the CT findings in atrophic rhinitis. These are nasal and paranasal mucosal thickening, small inferior and middle turbinates with atrophic mucosa and partial or total bony erosion. In addition, small maxillary sinuses are described. This finding may be equal to “silent sinus syndrome” where chronic obstruction cause negative maxillary sinus pressure, and with time the sinus walls collapse including the orbital floor, hence the patient may present with bilateral enophthalmos.
| Imaging for Chronic Sinusitis | | |
Sinus CT may show mucosal thickening in various degrees, from minimal mucosal thickening to severe opacification of the paranasal sinuses. Frequently, for various reasons, sinus CT shows no or only minimal mucosal abnormality. Those patients with persistent chronic sinusitis symptoms have taken anti-inflammatory medication as well as nasal spray; thus, the degree of mucosal inflammation is usually subtle. Some ear, nose, and throat surgeons schedule CT scan 4–6 weeks after antibiotic treatment, to see fine bone detail, which is often obscured by mucosal disease. Alternatively, those patients may have some other disease mimicking chronic sinusitis. At the other extreme, sinus CT may show severe opacification of all paranasal sinuses. Occasionally, bone thickening or sclerosis of the affected sinus is seen, suggestive of chronic periosteal inflammation. Polypoid soft tissue masses seen within the nasal cavity along with complete sinus opacification is suggestive of sinonasal polyposis, which is often associated with allergy or asthma. Chronic sinusitis is occasionally caused by fungi, such as aspergillosis or mucormycosis. There are three distinct categories of sinus fungal infection, allergic fungal sinusitis, invasive fungal sinusitis, and fungal ball (also called sinus mycetoma).
- Allergic fungal sinusitis patients are usually young and immunocompetent. Males are more frequently affected than females. Chronic inspissated secretion may appear in a high attenuation central region separated from the sinus wall on noncontrast CT.[35] The lesion involves multiple sinuses and is often bilateral. Bone destruction and expansion is frequent, mimicking tumor. Treatment is usually surgical debridement and antifungal medication. Allergic fungal sinusitis is most common in warm and humid areas. The CT findings usually are extensive to all paranasal sinuses, but can also be limited to one sinus. The clue to the diagnosis is hyperdense central fillings surrounded by less dense mucosal thickening. The hyperdense central fillings are due to thick inpissated allergic mucin. At MR, the allergic mucin shows signal void at T2 and high or intermediate signal at T1
- Invasive fungal sinusitis is seen in immunocompromised or diabetic patients. Acute invasive fungal sinusitis presents with a rapid clinical deterioration and has very poor prognosis. Imaging studies often show infiltrative soft tissue abnormalities with gross bone destruction. In this type, fungal hyphae are found in the mucosal lining of the sinuses, in the bone and in the perisinus soft tissue. The three invasive forms are acute, chronic and granulomatous. A fungus ball presents with foul smelling nasal discharge. A typical CT finding is advanced unilateral sinus opacification with centrally scattered microcalcifications that are the clue to the correct diagnosis. At MRI, the fungus ball has low T2 signal due to the micro-calcifications, but also due to the paramagnetic properties of iron and manganese in the fungal hyphae. In response to the fungal hyphae, the mucosal lining shows advanced thickening with high T2 signal surrounding the fungus ball. In invasive fungal sinusitis, the acute and chronic form can be differentiated by its presentation. The chronic form can simulate chronic rhinosinusitis, while the acute form presents with rapidly progressive symptoms, while the granulomatous form is rarely seen. The clue to diagnosis of invasive fungal sinusitis is to look for the obliteration of the fatty or soft tissue planes outside the sinuses. In invasive fungal sinusitis of the maxillary sinus, one should look for preantral and retroantral soft tissue masses. In addition, a nasal septal ulcer may be seen, referred to as an eschar. In case of invasive fungal sinusitis from the sphenoid sinus the orbital apex and cranial nerves may be affected and the patient presents with visual disturbances referred to as orbital apex syndrome
- Mucormycosis is one of the most common organisms in this entity. Fungal ball is a chronic fungal infection within the sinus, resulting in a well-defined expansile soft tissue mass with mottled foci of calcification.
Although MRI is not a primary imaging study for the evaluation of sinusitis, signal characteristics of sinus secretions were evaluated in chronic sinusitis patients. Som et al.[36] reported MR signal intensity changes as a function of protein concentration of sinus secretions. Normal sinus secretions consist predominantly of water; thus, it appears as low T1 and high T2 signal intensities. As the sinus secretions become more viscous, the T1 signal intensity increases and the T2 signal intensity slowly decreases. Furthermore, as sinus secretions become more desiccated and sludge-like, they appear as low intensity in both T1 and T2 signals,[37] and may become signal void. Fungal sinusitis is also associated with signal void on MRI as paramagnetic substance deposition such as manganese is fairly commonly seen with fungal infection.
| The Role of Sinus Computed Tomography for Chronic Sinusitis | | |
Despite a lack of evidence and problems related to the diagnosis of chronic sinusitis by CT, it remains the imaging study of choice for patients with chronic sinusitis. One of the roles of sinus CT is to determine whether a patient is truly suffering from chronic sinusitis as symptoms related to chronic sinusitis are often vague and nonspecific (i.e., headache or facial pain). Completely normal sinus CT performed when a patient is having symptoms without prior medical treatment should suggest other diagnoses. Sinus CT is also indicated for patients who do not respond to medical management and to evaluate any obstructive lesions such as a polyp, inverting papilloma, or sinonasal malignancy or anatomic abnormalities impairing mucociliary drainage of the sinus (insufficient evidence).
Once the diagnosis of chronic sinusitis is supported clinically and radiographically, an imaging evaluation for chronic sinusitis patients should include the extent of the disease. The distribution of sinus involvement may indicate a mucosal abnormality at the OMC. One should also look for potential complications associated with sinusitis, such as orbital cellulitis/abscess, mucocele or pyocele, epidural or brain abscess using a soft tissue window.
| The Role of Sinus Computed Tomography Before and After Endoscopic Sinus Surgery | | |
Chronic sinusitis develops from persistent or recurrent sinus inflammation, resulting in impaired ciliary function of the mucosa. FESS has been developed to repair mucociliary drainage of the sinus.[38],[39] Once surgery is indicated, CT is essential for providing detailed sinus anatomy as well as the status of OMC prior to FESS (insufficient evidence). Careful attention to key anatomic structures of the OMC is needed. These include ethmoid infundibulum, uncinate process, perpendicular plate and basal lamella of the middle turbinate, ethmoid bulla, nasofrontal duct, SER, and fovea ethmoidalis. Although certain anatomic variations such as concha bullosa, paradoxical middle turbinate, and nasal septum deviation can narrow the OMC,[40] whether or not these anatomical variations cause increased risk of developing chronic sinusitis is not known. FESS has been reported, primarily in the surgical literature, to provide improved clinical outcomes for patients with chronic sinusitis.[41],[42],[43] However, a study evaluating the methodologic quality of FESS investigations reports that most outcome studies of endoscopic sinus surgery lack a control group;[44] thus the efficacy of FESS has not been well established. Moreover, a substantial portion of patients who had endoscopic sinus surgery have recurrent symptoms and seek further medical care. Those patients may receive a second or third surgery and undergo additional CT scan before the additional surgery.
Common CT findings following FESS include uncinectomy, partial middle turbinectomy, and bulla ethmoidectomy. The extensive middle and inferior turbinectomies are no longer recommended since it may cause dryness or crusting of the nasal cavity, as well as turbulent air flow within the nasal cavity, resulting in the perception of difficulty in breathing through the nose. One needs to look for a residual uncinate process for a patient with persistent symptoms after sinus surgery.
| Differential Diagnosis for Sinusitis | | |
Many conditions may mimic the inflammatory patterns described, and differential diagnoses must always be considered. An antrochoanal polyp that occupies the maxillary sinus can be misinterpreted as an infundibular inflammatory pattern. The clue to the diagnosis is a small air-filled space superior in the sinus and soft tissue masses in the choana and with a polyp seen in the oropharynx. Periodontal infection may cause inflammation to the ipsilateral maxillary sinus as well as the ipsilateral anterior ethmoid and frontal sinuses, and hence mimic an OMC inflammatory pattern. It is mandatory that the technicians include the maxillary alveolar ridge in the scanning, to rule out or demonstrate an odontogenic origin. In case of dental filling artefacts, axial volume scanning will limit the dental artefacts to the axial plan.
Rhinolithiasis is a rare and an under-diagnosed finding that is caused by mineralization of an endogenous or exogenous foreign material.[45] The patients usually present with a foul-smelling nasal discharge. When dental amalgam is the cause, the ethmoid infundibulum or the middle meatus may be obstructed and cause rhinosinusitis that mimic the infundibular or OMC patterns. In addition, an ectopic molar tooth free inside the maxillary sinus can give the same imaging appearance. Several systemic diseases may show or present with sinonasal symptoms that may mimic or be equal to the patterns of inflammatory rhinosinusitis. Fungal rhinosinusitis can imitate all five inflammatory patterns and must be considered in all patients with chronic rhinosinusitis.
Tumors are rare in the paranasal sinuses and contributing to only 1% of all malignant tumors. Therefore, malignant tumors are commonly interpreted as rhinosinusitis. All solitary nasal polyps should be considered for histopathologic examination. Destruction of adjacent bone at CT is one clue to suspect a malignant tumor.
| Summary | | |
Most cases of uncomplicated acute and subacute rhinosinusitis are diagnosed clinically and should not require any imaging procedure. CT of the sinuses without contrast is the imaging method of choice in patients with recurrent acute sinusitis or chronic sinusitis, or to define sinus anatomy before surgery. In patients with suspected sinonasal mass or suspected orbital and/or intracranial complication of sinusitis, MRI and CT are complementary studies. Understanding the different types of sinusitis and knowing their particular radiologic features allows the radiologist to play a crucial role in alerting the clinician to use appropriate diagnostic techniques for confirmation.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1]
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