Rhinosinusitis and the role of imaging

RHINOSINUSITIS: AN OVERVIEW

Rhinosinusitis, the symptomatic inflammation of the nasal cavity and sinuses,¹ can be divided into rhinitis and sinusitis, yet the two terms are often combined because the nasal mucosa and sinus mucosa are often inflamed synchronously.² It is one of the most commonly treated conditions in ambulatory care, but the presentation is often similar to that of other upper respiratory tract infections, and accurate diagnosis is difficult.³ Symptoms commonly include nasal drainage, nasal obstruction, and facial pain or pressure. Other symptoms can include fever, headache, cough, ear pain or pressure, and anosmia.⁴

The diagnosis is generally based on symptoms and their duration.¹ Acute rhinosinusitis is defined as up to 4 weeks of purulent nasal drainage accompanied by “nasal obstruction, facial pain-pressure-fullness, or both.”¹ In most cases, symptoms resolve in 7 to 10 days. Rhino-sinusitis is subacute if symptoms persist beyond 4 weeks and less than 12 weeks, and chronic when symptoms last more than 12 weeks with objective evidence of mucosal inflammation visualized endoscopically or radiographically. Chronic rhinosinusitis may present with or without nasal polyps.¹

Recurrent rhinosinusitis is defined as 4 or more episodes of acute rhinosinusitis per year with no symptoms between episodes.¹

INFECTIOUS VS NONINFECTIOUS

Rhinosinusitis can be infectious or noninfectious. Infectious rhinosinusitis is classified as viral, bacterial, or fungal (Table 1).

MANAGEMENT: GENERAL APPROACHES

When patients present with symptoms of acute rhinosinusitis believed to be uncomplicated based on review of history, observation is recommended for a period of 7 to 10 days,^1,5 with symptomatic treatment including analgesics, intranasal glucocorticoids, intranasal saline irrigation, decongestants, and antihistamines.^1,3,5 Analgesics including acetaminophen and nonsteroidal anti-inflammatory drugs are useful for relief of pain and fever.³ Intranasal corticosteroids are useful for reducing inflammation of nasal mucosa, thereby facilitating sinus drainage.^1,5

IMAGING OPTIONS

Rhinosinusitis is a clinical diagnosis. Imaging is reserved for cases of complicated rhinosinusitis, recurrent sinusitis, chronic rhinosinusitis, and immunocompromised patients.⁴ Imaging findings do not always correlate with symptoms. It is estimated that 3% to 40% of asymptomatic patients may have sinus abnormalities on computed tomography (CT). Thus, imaging should corroborate the presenting signs and symptoms.¹⁹ Indications for imaging are based on the classification of rhinosinusitis¹⁹ (Figure 1).

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Figure 1

Approach to imaging in rhinosinusitis.

IMAGING IN ACUTE UNCOMPLICATED VIRAL OR BACTERIAL RHINOSINUSITIS

Referring back to our case of the 31-year-old woman, she presented with signs and symptoms consistent with acute, uncomplicated, likely bacterial rhinosinusitis, based on the duration of symptoms and double sickening. Acute, uncomplicated bacterial or viral rhinosinusitis is a clinical diagnosis, and patients who meet diagnostic criteria for uncomplicated rhinosinusitis should not undergo imaging.^4,19,22,23

Plain radiography in acute uncomplicated bacterial rhinosinusitis carries a sensitivity of 76% and a specificity of 79%.²⁰ But even in the presence of positive findings such as air fluid levels, plain radiography cannot distinguish between viral and bacterial infections and therefore is not recommended.³

In one study, CT of the nasal passages and sinuses performed in otherwise healthy patients who presented with “common cold” symptoms revealed a high prevalence of meatal and sinus findings, including occlusion of the ethmoid infundibulum in 77% of patients, abnormalities of one or both maxillary sinuses in 87%, and ethmoid sinus abnormalities in 65% of patients. On repeat CT 2 weeks later, these findings had resolved or clearly improved in 79% of patients without antibiotic treatment.²⁴ Thus, CT and MRI are not useful in the context of uncomplicated sinusitis. In addition, CT exposes patients to unnecessary radiation.⁴ When complications of rhinosinusitis or spread of infection are suspected, imaging can be considered.²⁵

IMAGING IN ACUTE COMPLICATED VIRAL OR BACTERIAL RHINOSINUSITIS

In patients with suspected rhinosinusitis who present with symptoms indicating spread of infection beyond the sinuses and nasal cavity, imaging may be performed for diagnostic purposes.¹⁵

CT without contrast enhancement is the gold standard of sinus imaging and often the first test performed when complications of rhinosinusitis are suspected, as it affords the best delineation of bone and allows for visualization of bony integrity and erosion. Findings on CT suggestive of sinusitis include thickened mucosa (> 4 mm), air fluid levels, and opacification of the sinuses.²⁵

MRI may be indicated when complications such as aggressive intracranial or intra-orbital spread of infection or cavernous sinus thrombosis is suspected, and for definition of soft-tissue masses.¹⁹ T1-weighted MRI is recommended to evaluate abscess or extension of infection past the sinuses, and T2-weighted MRI can differentiate inflammatory mucosa from soft-tissue masses. Contrast-enhanced MRI is recommended if cavernous sinus thrombosis is suspected.

When complications involving the orbit or cranium are suspected, the American College of Radiology recommends CT with contrast enhancement or MRI without contrast for evaluation.¹⁹ While the American College of Radiology notes that intravenous contrast is generally not needed, IDSA guidelines recommend contrast-enhanced CT with axial and coronal views in the case of suspected complications.⁵

IMAGING IN RECURRENT ACUTE OR CHRONIC RHINOSINUSITIS

Recurrent acute rhinosinusitis is defined as 4 or more episodes of acute rhinosinusitis per year, with no symptoms of rhinosinusitis between episodes. Chronic rhinosinusitis is symptom duration of more than 12 weeks with objective evidence of mucosal inflammation visualized endoscopically or radiographically.¹ In either case, and in cases of sinonasal polyposis, imaging is warranted for evaluation and operative planning if surgery is warranted.¹⁹

Noncontrast CT is indicated as part of the workup before any surgical intervention, as it provides the best preoperative information, including delineation of complex anatomy, and may even be used intraoperatively to guide surgery. MRI is not first-line due to lack of bony detail. Cone-beam CT is useful in the assessment of odontogenic sinusitis and maxillary sinus involvement.¹⁹ Plain radiography may reveal foreign bodies or assist in diagnosing anatomic variants, but is not used clinically due to the superiority of CT.

In patients with a history of recurrent or chronic sinusitis who have had imaging in the past, in the absence of new symptoms, imaging does not provide further information and findings often remain unchanged. Repeat imaging is not necessary unless clinical signs or symptoms have changed.⁵

IMAGING IN FUNGAL SINUSITIS

Depending on the type of fungal infection suspected, imaging may be warranted.¹⁹ For saprophytic fungal infestations, which are frequently asymptomatic, the diagnosis is made clinically, and no imaging is required for diagnosis.

Fungus ball, another noninvasive fungal presentation, may be evaluated with CT of the sinuses or panoramic dental imaging; it appears as hyperattenuated material filling a single sinus.

Allergic fungal rhinosinusitis is the most common form of fungal sinus disease and is evaluated with CT or MRI. Classic findings on CT include the “double-density” sign caused by thick fungal mucin surrounded by hyper-plastic mucosa. MRI with T1 and T2 weighting can be used to support the diagnosis.

When invasive acute or chronic fungal infection is suspected, contrast-enhanced CT or contrast-enhanced MRI can be used to visualize the sinuses, brain, and orbits.⁹ CT findings of invasive infection can include hypoattenuating mucosal thickening over the affected sinus and nasal cavity, bony erosion, and findings extending beyond the sinus and nasal cavities. MRI is time-consuming to obtain yet favorable for evaluating intracranial and intraorbital spread.¹⁰

IMAGING IN ALLERGIC RHINITIS

Imaging is not routinely recommended in patients who present with symptoms of allergic rhinitis. When patients present with symptoms of rhinosinusitis (as opposed to rhinitis, which affects only the nasal cavity), signs of complicated infections, signs of neoplasm, or persistence of symptoms and chronic rhinosinusitis, imaging may be warranted. As in the case of complicated rhinosinusitis, CT without contrast is typically the first imaging test recommended.¹²

THE BOTTOM LINE

Acute, uncomplicated rhinosinusitis remains a clinical diagnosis. Imaging should only be used in the case of complicated sinus infections, recurrent or chronic sinus disease, or in the case of surgical planning.²⁵ Yet imaging is still frequently performed despite these recommendations.⁴

Imaging when not clinically indicated is associated with increased healthcare costs and unnecessary exposure to radiation and, in some cases, intravenous contrast material.⁴ Imaging in the setting of acute uncomplicated rhinosinusitis has not been proven to change clinical outcomes.²⁶ Clinical judgment to carefully select patients who are appropriate for imaging, as well as selecting low-dose radiation options when available, are ways to minimize imaging utilization.