Acute Sinusitis (Acute Rhinosinusitis): Classification, Clinical Manifestations, Diagnosis, and Treatment

Acute rhinosinusitis (ARS), commonly referred to as acute sinusitis, is inflammation of one or more paranasal sinuses accompanied by inflammation of the nasal mucosa.

According to the European Rhinologic Society, ARS lasts less than 12 weeks. The American Academy of Otolaryngology, by contrast, defines it as lasting less than 4 weeks.

In the European Position Paper on Rhinosinusitis and Nasal Polyps (EPOS 2020), European and international rhinologic societies recommend using the term rhinosinusitis. This term highlights that rhinitis and sinusitis are closely connected and often coexist. The nasal cavity and paranasal sinuses share a continuous mucosal lining and a common mucociliary clearance system, which is why inflammation frequently affects both areas.

Classification

By localization:

• Ethmoiditis: inflammation of the ethmoidal air cells (ethmoidal labyrinth).
• Maxillary sinusitis: inflammation of the maxillary sinuses.
• Frontal sinusitis: inflammation of the frontal sinuses.
• Sphenoid sinusitis: inflammation of the sphenoid sinuses.
• Pansinusitis: inflammation of all paranasal sinuses.

By pathogenesis:

• Rhinogenic (non-odontogenic) sinusitis: infection spreads from the nasal cavity into the paranasal sinuses.
• Odontogenic sinusitis: infection originates from the teeth or maxillofacial region and extends into the paranasal sinuses.

By pathomorphology:

• Catarrhal sinusitis: marked mucosal edema and hyperemia without pathological discharge;
• Serous sinusitis: clear (serous) fluid in the sinuses with mucosal edema and hyperemia;
• Purulent sinusitis: thick purulent exudate with persistent mucosal edema and hyperemia;
• Necrotizing sinusitis: destruction of the mucosa and underlying tissues with sloughing of necrotic material.

3D Models: Acute Maxillary Sinusitis

Acute Catarrhal Maxillary Sinusitis

Acute Serous Maxillary Sinusitis

By clinical course:

• Acute viral rhinosinusitis (AVRS): lasts up to 7–10 days with no signs of bacterial infection;
• Acute post-viral rhinosinusitis: lasts more than 10 days without clear signs of bacterial infection;
• Acute bacterial rhinosinusitis (ABRS): typically presents with purulent nasal discharge, a second fever spike 5–7 days after symptom onset, unilateral facial pain, and elevated CRP.

Normal Anatomy

The paranasal sinuses include four paired groups: the maxillary, frontal, and sphenoidal sinuses, as well as the ethmoid labyrinth, which is made up of ethmoidal air cells. Like the nasal cavity, the paranasal sinuses are lined with ciliated epithelium. Normally, they are air-filled and ventilate and drain through natural ostia that open into the nasal cavity.

Maxillary sinuses (sinus maxillaris)

The maxillary sinuses are paired sinuses located within the body of the maxilla. They are the largest paranasal sinuses, with an average volume of 10–13 mL per side.

The sinus has five walls: anterior, posterior, superior, inferior, and medial.

• Medial wall: borders the nasal cavity and communicates via the natural ostium in the upper part of the wall. Drainage occurs through the semilunar hiatus (hiatus semilunaris) into the middle nasal meatus.
• Superior wall: formed by the floor of the orbit. It is the thinnest wall and may have natural dehiscences, which contributes to the risk of orbital complications.
• Inferior wall: lies in close relation to the alveolar process of the maxilla. In some cases, the sinus is separated from premolar and molar roots by only a thin bony plate or even just mucosa. This close anatomic relationship can contribute to odontogenic sinusitis.
• Anterior wall: faces the cheek and is relatively thick. Above the canine tooth, however, there is a thinner area known as the canine fossa (fossa canina), which is often used for surgical access.
• Posterior wall: separates the sinus from the pterygopalatine fossa and the pterygoid process of the sphenoid bone.

Frontal sinuses (sinus frontalis)

The frontal sinuses are paired sinuses located in the frontal bone. They are rarely symmetrical and may contain septations and recesses. Their volume ranges from 2 to 7 mL.

• Anterior wall: the thickest wall and lies adjacent to the forehead.
• Posterior (cranial) wall: the thinnest wall and lies adjacent to the anterior cranial fossa.
• Inferior wall: forms the roof of the orbit.
• Medial wall: separates the two sinuses and is often deviated to one side.

The frontal sinus outflow tract is located along the inferior wall of the sinus. It connects the frontal sinus to the nasal cavity and opens through the semilunar hiatus into the middle nasal meatus. The tract is narrow and tortuous and may be up to 1.5 cm long.

Ethmoidal labyrinth (sinus ethmoidalis)

The ethmoidal labyrinth is composed of numerous air cells (8–10 on each side) arranged along the perpendicular plate of the ethmoid bone.

The cells are grouped into anterior, middle, and posterior compartments and are separated by thin bony septa.

• Laterally, the labyrinth borders the orbit through the thin lamina papyracea (orbital plate of the ethmoid bone). Medially, it borders the nasal cavity.
• Superiorly, it is bounded by the cribriform plate (lamina cribrosa). This plate forms the floor of the anterior cranial fossa and contains openings for the olfactory nerves.
• Inferiorly and posteriorly, it borders the maxillary and sphenoid sinuses.
• The anterior and middle ethmoidal cells drain via the semilunar hiatus into the middle nasal meatus. The posterior ethmoidal cells open into the superior nasal meatus.

Sphenoid sinuses (sinus sphenoidalis)

The sphenoid sinuses are paired sinuses located within the body of the sphenoid bone. They are separated by a thin bony septum (the medial wall) and may be asymmetric. The average volume of each sphenoid sinus is approximately 5–6 mL.

• Superior wall: thin; it forms the floor of the sella turcica and contributes to the boundary of the middle cranial fossa.
• Inferior wall: thick; it forms the roof of the nasopharynx.
• Posterior wall: located within the sphenoid bone.
• Anterior wall: faces the nasal cavity and partially borders the posterior ethmoidal cells.
• Lateral wall: adjacent to the cavernous sinus, internal carotid artery, and cranial nerves, including the optic (II), oculomotor (III), trochlear (IV), and abducens (VI) nerves.

The anterior wall contains a natural ostium (aperture) that allows the sinus to communicate with the nasal cavity. The ostium opens into the sphenoethmoidal recess, which is located in the superior nasal meatus.

Epidemiology

ARS is among the most common ENT conditions. Each year, an estimated 12%–14% of adults and 6%–7% of children experience at least one episode of ARS. The male-to-female ratio is approximately 1:1.

In adults, maxillary sinusitis is most common (61%), followed by frontal sinusitis (32%), ethmoiditis (9%), and sphenoid sinusitis (2%). In children, ethmoiditis (28%) and maxillary sinusitis (25%) predominate, while frontal and sphenoid involvement is uncommon. Overall, no more than 2% of ARS cases progress to bacterial sinusitis.

Epidemiology

Pathogens associated with ARS

• Viruses: rhinovirus, respiratory syncytial virus (RSV), influenza and parainfluenza viruses, coronavirus, adenovirus, enterovirus.
• Bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Streptococcus intermedius, Streptococcus constellatus, Fusobacteria spp.
• Fungi: Mucor, Rhizomucor, Aspergillus.

Acute fungal rhinosinusitis occurs primarily in immunocompromised patients, including those with HIV infection, individuals receiving immunosuppressive therapy, and patients undergoing active cancer treatment. In these settings, an invasive form of fungal rhinosinusitis may develop.

Routes of infection

• Rhinogenic ARS: infection spreads from the nasal cavity into the paranasal sinuses.
• Odontogenic ARS: infection spreads from the maxillary dental region. This is most often seen after perforation of the maxillary sinus floor during tooth extraction or dental implantation and in association with periapical abscesses or periodontitis involving upper molars and premolars.

Pathophysiology

Acute inflammation of the paranasal sinuses is usually multifactorial. As ARS develops, the following changes occur:

• Mucociliary clearance becomes impaired. Edema in the nasal cavity narrows key drainage pathways and can obstruct the natural sinus ostia. As swelling extends into the paranasal sinuses, ventilation and drainage worsen. Secretions then accumulate, making microbial colonization and invasion more likely.
• When an ostium is obstructed, negative pressure can develop within the sinus. This promotes fluid transudation into the sinus cavity. The resulting fluid buildup can then support bacterial overgrowth.
• The sinus mucosa becomes hyperemic and inflamed. Early secretions are often mucous or serous. If a bacterial infection develops, the contents become purulent.
• On histopathology, goblet cell hyperplasia may be seen, along with inflammatory infiltrates that commonly include lymphocytes and neutrophils.
• In necrotizing disease, including invasive fungal rhinosinusitis, the mucosa and underlying tissues can undergo destructive changes with necrosis and tissue breakdown.

Clinical Manifestations

ARS typically presents with facial pain or pressure, nasal congestion, nasal discharge, reduced sense of smell, and fever. Discharge may be unilateral or bilateral and may be mucoid or purulent.

Symptoms by etiology

• In rhinogenic ARS, symptoms occur in the setting of acute rhinitis, and many patients report worsening around days 4–7 after onset. Fever may be low-grade or high-grade.
• In odontogenic ARS, tooth pain on the affected side is characteristic, and patients may notice an unpleasant taste in the mouth.
• In maxillary sinusitis, pain is often localized to the cheek on the affected side and may be accompanied by a sensation of pressure or fullness. In frontal sinusitis, pain is typically felt in the forehead and supraorbital region. In both conditions, pain often worsens when bending forward.
• In ethmoiditis, pain is often intense at the bridge of the nose and around the eyes. Some patients also report anosmia or an unpleasant odor sensation. In sphenoid sinusitis, occipital pain and a sense of head heaviness may predominate.
• Acute invasive fungal rhinosinusitis differs from viral and bacterial disease by causing severe, progressive facial pain and numbness. Bleeding may occur when necrosis is extensive. In some cases, however, symptoms may be minimal or absent.

With acute sinusitis of any etiology and location, orbital or intracranial complications may occur if purulent contents extend beyond the paranasal sinuses.

Diagnosis of Acute Sinusitis

ARS is primarily a clinical diagnosis. According to EPOS 2020, ARS is a sudden-onset condition with at least two symptoms, including at least one of the following:

• Nasal congestion, obstruction, or blockage;
• Nasal discharge (anterior rhinorrhea or postnasal drip);
• Facial pain or pressure;
• Reduced or lost sense of smell.

Additional symptoms may include:

• Fever;
• Cough;
• Fatigue.

Symptom duration is less than 12 weeks, or less than 4 weeks according to the American Academy of Otolaryngology definition.

In ABRS, a second fever spike above 38 °C may occur. This is often accompanied by marked unilateral facial pain, purulent nasal discharge, and overall clinical worsening.

ENT Examination

Anterior rhinoscopy or nasal endoscopy often shows mucosal erythema and edema. Discharge may be visible along the nasal floor or draining from the middle nasal meatus.

Tenderness may be present on palpation at trigeminal nerve exit points, particularly along the ophthalmic and maxillary branches. Percussion over the projected areas of the paranasal sinuses may also elicit pain.

Sinus X-rays

Routine plain radiography (sinus X-rays) is not recommended because of limited sensitivity and specificity. Opacification over the paranasal sinuses may reflect mucosal edema or a fluid level. However, similar findings can also be seen with viral infection and allergic disease, so X-rays do not reliably distinguish etiologies.

Computed Tomography (CT) of the Paranasal Sinuses

CT of the paranasal sinuses is recommended when complications are suspected, when symptoms are severe, and in cases of recurrent or suspected fungal rhinosinusitis. Mucosal thickening greater than 5–7 mm or the presence of pathological contents within a sinus supports the diagnosis of sinus inflammation. In invasive fungal or necrotizing rhinosinusitis, CT may show bony wall destruction.

Laboratory Tests

Laboratory tests are not routinely indicated in typical, uncomplicated cases.

• Blood tests may be useful in complicated disease and can help differentiate bacterial from viral rhinosinusitis. Leukocytosis, an elevated neutrophil count, and increased ESR and CRP can suggest a bacterial etiology. However, these findings may be mild or absent.
• Microbiological testing of nasal or sinus secretions is generally reserved for severe, prolonged, or atypical cases Cultures may be obtained for bacterial and fungal pathogens, and susceptibility testing can guide antimicrobial therapy.

Paranasal Sinus Puncture

Paranasal sinus puncture is performed for both therapeutic and diagnostic purposes. In most cases, this involves puncture of the maxillary sinus. It may be considered when symptoms fail to improve with treatment, when the clinical course is atypical or prolonged, or when complications develop. The collected secretions should be sent for microbiological testing.

Additional Diagnostic Steps

• Patients with suspected odontogenic rhinosinusitis should be referred for dental evaluation.
• If acute invasive fungal rhinosinusitis is suspected, biopsy of necrotic sinonasal tissue is required.

Treatment of Rhinosinusitis

Management is guided by the suspected etiology and clinical form of the disease:

• For acute viral rhinosinusitis, treatment is primarily symptomatic. Saline nasal irrigation can help clear secretions and improve nasal comfort. Intranasal corticosteroids may be used to reduce inflammation, and short-term decongestants can be considered. For fever or significant pain, NSAIDs or acetaminophen are appropriate. Antihistamines are recommended only when an allergic component is present, because they can thicken secretions and worsen nasal obstruction.
• For acute bacterial rhinosinusitis, systemic antibiotics may be prescribed (e.g., penicillins, cephalosporins, or macrolides). At the same time, evidence suggests that antibiotics do not always meaningfully shorten the illness or reduce symptom severity and may cause adverse effects. For that reason, the decision to treat should be individualized.

Paranasal sinus puncture may be considered when treatment is ineffective, when the course is atypical or prolonged, or when complications are suspected. In most cases, the procedure involves the maxillary sinus and allows evacuation of pathological contents.

• Odontogenic rhinosinusitis requires coordinated care with a dental specialist. The key step is to address the dental source, such as by treating or extracting the affected tooth. Antibiotic therapy is also be used when indicated.
• Acute invasive fungal rhinosinusitis requires hospitalization and a combined surgical and medical approach. Treatment includes surgical debridement of affected tissues and initiation of systemic antifungal therapy.