The diagnosis of bacterial sinusitis can be confirmed with the assistance of imaging techniques. These range from ultrasonography and plain film radiology (PFR) to advanced computed tomography (CT) and magnetic resonance imaging (MRI).
Range of Radiological Studies for Diagnosis of Bacterial Sinusitis at Its Complication:
• PFR studies provide only subtle shadows, diffuse contours, and imprecise indirect signs, and are therefore insensitive and inadequate for accurate staging or assessing disease progression or healing.
• CT and MRI provide visualization of the sinus pathology and anatomy, and allow for comparison with a baseline during repeated imaging.
• MRI is not commonly used for routine evaluation of paranasal sinuses, but is the modality of choice if intracranial extension is suspected.
• Can detect the presence of fluid in the sinuses in acute infection.
• Relatively inexpensive.
• Safe because no ionizing radiation is used.
• Discriminates between mucosal thickening and retained secretion better than other techniques.
• Limited bone penetration restricts its use to frontal and maxillary sinuses alone.
• Is not specific in children less than 4 years of age, or in adults with allergies.
• Concordance with sinus aspiration has been reported in about 90% of cases.
Ultrasound showing fluid in the maxillary sinus
Plain Film Radiography:
• The Culdwell view most clearly shows the frontal and ethmoid sinuses.
• The Water’s occipitomental view shows the frontal and maxillary sinuses .
• The lateral view shows the sphenoid and posterior ethmoid sinuses and the extent of pneumatization and depth of the maxillary and frontal sinuses.
• The submentovertex view shows the sphenoid and ethmoid sinuses, and the posterior portion of the maxillary sinuses.
The key positive radiographic findings in PFR
• Complete opacification
• Air-fluid level
• Mucosal thickening greater than 4 mm
These findings are not specific for acute infection, but are useful in confirmation along with other signs and symptoms.
Plain X ray showing right maxillary sinusitis:
Advantages and disadvantages of PFR as compared with CT
• Relatively low radiation dose (1/8 that of limited CT and 1/30 that of standard CT)
• Less expensive
• Can be used in children without sedation
• Useful in the diagnosis of maxillary sinusitis, is of some diagnostic help in frontal and splenoid infection, but less so in ethmoid infection
• Poor visualization of the osteomeatal complex (OMC)
• Less specific and sensitive than CT for analysis of the degree of sinus abnormalities; because of this limitation, its use has declined and it has now been replaced by CT
• Of no diagnostic help in children younger than 6 years old, unless they suffer from complicated infection
Recurrent inflammatory sinusitis can be divided into five different patterns based on the CT appearance: infundibular, OMC, sphenoethmoidal recess, polyposis, and sporadic. CT imaging provides information about the status of the bony walls of the sinuses, the condition of adjacent structures (i.e., midface, orbit, brain), and the nature of the material within the sinuses.
CT of right maxillary sinusitis
Advantages and disadvantages of CT as
compared with PFR
• Greater accuracy in evaluating paranasal sinuses, because of
a) Improved contrast resolution in the detection of bone, and of bone-air and bone-soft tissue interfaces
b) Ability to detect very small structures through greater resolution
• Greater accuracy in assessing the anterior ethmoid air cell anomalies and the OMC
• Better visualization of maxillary mucosal thickening or posteriorly located retention cysts
• It displays structural abnormalities, congenital or acquired, predisposing to sinusitis (e.g., deviated septum or elongated uncinate process)
• Necessary in planning functional endoscopic sinus surgery (FESS)
• CT is better than PFR (but inferior to MRI) in assessing soft-tissue structures inside or in proximity to the sinuses
• Advantageous in children because their sinuses are small and are often asymmetrical and difficult to evaluate
• Greater exposure to radiation
• Greater cost
• May require the use of sedation in children
Indications for CT
• Evaluation of complicated bacterial sinusitis
• Patients with multiple recurrences
• In the presence of clinical signs and symptoms that suggest sinusitis, a negative PFR does not exclude infection, and should be followed by CT
• Patients with nonresponding or protracted symptoms
Several studies reported CT abnormalities in individuals with recent viral colds (42% of children, and more than 75% of adults). Unanswered is the question of what is the clinical significance of positive findings in asymptomatic patients (in infants < 1 year [39–59%], in children [31–39%],and in adults [7–28%]).
Limited CT examination of four to five images offers lower cost and reduced exposure to radiation than standard CT. An initial tomogram can assist in selecting the best slice levels.
CT of left maxillary and ethmoid sinusitis
Magnetic Resonance Imaging:
• The imaging method of choice in the diagnosis of complications of bacterial sinusitis (orbital, intracranial, or deep-facial extension); gadolinium-enhanced MRI is used for studying suspected intracranial complications
• Possesses excellent soft-tissue contrast
• High-resolution images of slice thickness equal to or less than those used in CT scanning that can produce three-dimensional views can be obtained
• No exposure to radiation
• The method of choice for those allergic to contrast material or who have vascular occlusions
MRI of maxillary sinuses
• Difficult to perform in young patients (may require sedation) or claustrophobic patients
• Inadequate sensitivity in detecting sinusitis
• Cannot be performed in patients with fresh, metallic foreign bodies.
Use of Imaging Techniques in Allergic, and Fungal Sinusitis.
• Allergic sinusitis generally produces less mucosal and turbinate edema and air-fluid levels than bacterial sinusitis.
• Bilateral and symmetrical sinus involvement, which increases during the pollen season, is more often found in allergic sinusitis.
Use of Imaging Techniques in Fungal Sinusitis
• The characteristic CT finding in fungal bacterial sinusitis is nonspecific thickening, often with focal increased attenuations (calcium sulfate and calcium phosphate deposits). Such densities can also be seen in chronic bacterial sinusitis or cystic fibrosis. Bone thinning and osseous destruction, and extension to surrounding tissues, can occur.
• Mycetomas can be observed by MRI.