Acute sinusitis

Last revised by David Bassett on 27 May 2024

Acute sinusitis (rare plural: sinusitides) is an acute inflammation of the paranasal sinus mucosa that lasts less than four weeks and can occur in any of the paranasal sinuses. If the nasal cavity mucosa is also involved - rhinitis - then the term rhinosinusitis may be used.

Acute sinusitis typically presents with fever, headache, postnasal discharge of thick sputum, nasal congestion and an abnormal sense of smell. Acute sinusitis is a clinical diagnosis characterized by symptom duration of less than 4 weeks 11.

Acute sinusitis usually occurs following a viral upper respiratory tract infection. Dental caries, periapical abscess and oroantral fistulation may lead to a spread of infection to the maxillary sinus. Cystic fibrosis and allergy are risk factors.

Other anatomical variants that may predispose to the inflammation include nasal septal deviation, a spur of the nasal septum and/or frontoethmoidal recess variants.

Patients in an intensive care setting are at an increased risk of acute sinusitis.
Risk factors identified include 10:

  • indwelling nasogastric tubes and/or endotracheal tubes

    • especially nasotracheal routing

  • prolonged admission

  • younger age

Imaging findings of acute sinusitis are non-specific and can be seen in a large number of asymptomatic patients (up to 40%) 11. Imaging findings should be interpreted with clinical and/or endoscopic findings.

A gas-fluid level is the most typical imaging finding. However, it is only present in 25-50% of patients with acute sinusitis 4.

Opacification of the sinuses and gas-fluid level best seen in the maxillary sinus. It does not allow assessment of the extent of the inflammation and its complications. Ethmoidal and sphenoidal sinuses are difficult to assess on plain radiography.

The most common method of evaluation. Better anatomical delineation and assessment of inflammation extension, causes, and complications.

Described findings include

  • peripheral or central mucosal thickening

  • gas-fluid levels in the paranasal sinuses

  • gas bubbles within the fluid / bubbly secretions

  • obstruction of the ostiomeatal complexes.

Rhinitis, often associated with sinusitis, is often characterized by thickening of the turbinates with obliteration of the surrounding air channels. This should not be confused with the normal nasal cycle.

The maxillary dentition should also be assessed as around 20% of maxillary sinus infections are odontogenic 11.

Signal characteristics of the affected regions include

  • T1: mucosal thickening is isointense to soft tissue and fluid is hypointense

  • T2: both mucosal thickening and fluid are, to a variable degree, hyperintense

  • T1 C+ (Gd): inflamed mucosa enhances whilst fluid does not

Although not the primary mode of investigation, sonography may be used to screen for maxillary sinusitis; the perturbation of the normal air/fluid ratio in sinusitis alters the acoustic impedance of the usually aerated space. Normal and abnormal maxillary sinus features may be differentiated as follows:

  • normal maxillary sinus

    • a series of horizontal reverberation artifacts extend into the far-field, diminishing with each successive iteration, parallel to the prominent near field linear echogenic cortex of the maxilla 9

    • the far-field is ill-defined, and the posterior wall of the sinus is not visible

  • abnormal maxillary sinus

    • complete sinusogram 5

      • sagittal insonation reveals the absence of horizontal reverberation artifacts, replaced by an anechoic space

      • posterior wall appears in the far-field as an echogenic stripe 

      • transverse insonation reveals this echolucent space bordered by the medial and lateral walls

      • this indicates the sinus is fluid-filled and is highly suggestive of sinusitis in the appropriate clinical context

    • partial sinusogram

      • sagittal visualization of a portion of the posterior wall, with adjacent horizontal reverberation artifacts

      • medial/lateral walls obscured 

      • nonspecific finding, but increased specificity if partial sinusogram present while semi-supine and absent when supine 6

        • this indicates an air-fluid level and is considered positive for sinusitis

        • presence when both semi-supine and supine thought to be indicative of mucosal thickening 7

Acute sinusitis is usually treated conservatively with medical treatment until the inflammation subsides +/- treatment of the cause, e.g. dental caries. If it becomes chronic sinusitis, functional endoscopic sinus surgery (FESS) may be considered.

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