Paranasal Sinuses

Acute Bacterial Sinusitis

A bacterial infection of the paranasal sinuses that most often develops as a complication of a viral upper respiratory infection. Diagnosis is clinical and depends primarily on the pattern and trajectory of symptoms.

Upper AirwayBacterial InfectionClinical DiagnosisAntibiotic Therapy

Clinical Vignette

The cold was getting better—so why is she sick again?

Recognize worsening after initial improvement as one of the characteristic clinical presentations of acute bacterial sinusitis.

An 8-year-old presents with worsening nasal congestion, nasal discharge, and cough. Eight days ago, she developed rhinorrhea, sore throat, and a mild cough consistent with a viral upper respiratory infection.

By illness day 5, her symptoms seemed to be improving and she had returned to normal activity. Over the last 2 days, however, her nasal congestion and daytime cough have become substantially worse, and she developed a new fever to 39.1°C (102.4°F).

Examination shows mucopurulent nasal discharge and edematous nasal mucosa. She is breathing comfortably with normal oxygen saturation and clear lungs.

Her parent asks whether this is simply the same cold taking longer than expected.

Your clinical reasoning task

Does this still fit the expected trajectory of an uncomplicated viral URI, or does the initial improvement followed by new fever and worsening respiratory symptoms suggest acute bacterial sinusitis?

Anatomy & Localization

Localize sinusitis to the paranasal sinuses

Sinus anatomy changes throughout childhood, and the location of infection helps predict both symptoms and complications.

Anterior and lateral anatomy of the paranasal sinuses

Paranasal sinus anatomy shown in anterior and lateral views. The frontal, ethmoid, sphenoid, and maxillary sinuses are highlighted to demonstrate their relative location and relationships to surrounding structures.

Adapted from OpenStax College, Anatomy & Physiology, licensed under CC BY 3.0. Modified for PediAtlas.

Maxillary & Ethmoid Sinuses

The maxillary and ethmoid sinuses begin developing during fetal life and are present, although small, at birth. They continue to enlarge throughout childhood.

Frontal & Sphenoid Sinuses

The frontal and sphenoid sinuses develop later, typically beginning around 2–3 years of age, and remain relatively rudimentary during early childhood.

Development

Sinus anatomy changes with age

A young child does have paranasal sinuses—but not the same fully developed sinus anatomy as an adolescent. Maxillary and ethmoid disease can occur early in life, while the frontal and sphenoid sinuses become increasingly relevant as children grow.

Middle Meatus

The maxillary, frontal, and anterior ethmoid sinuses drain into the middle meatus. Inflammation and edema around these drainage pathways can obstruct sinus outflow and impair clearance of secretions.

Superior Meatus

The sphenoid and posterior ethmoid sinuses drain more posteriorly through the superior meatus, providing a separate drainage pathway into the nasal cavity.

Clinical Anatomy

Why drainage matters

Sinuses are lined by ciliated respiratory epithelium. Viral inflammation can produce mucosal edema, obstruct the sinus ostia, and impair mucociliary clearance—creating conditions that favor bacterial growth.

Complication Risk

Anatomy predicts complications

The paranasal sinuses sit immediately adjacent to important structures. Ethmoid sinusitis is particularly associated with orbital complications, while frontal sinusitis can extend intracranially. New eye findings, severe headache, neurologic symptoms, or other signs of extension should therefore change the urgency of evaluation.

Pathophysiology

A viral URI sets the stage for bacterial sinusitis

Acute bacterial sinusitis usually develops when inflammation from a viral upper respiratory infection disrupts normal sinus drainage and mucociliary clearance.

Viral URI

A respiratory virus infects the nasal and sinus mucosa, triggering inflammation and increased mucus production.

Mucosal edema

Inflammation causes swelling of the respiratory mucosa surrounding the narrow sinus drainage pathways.

Ostial obstruction

Edema narrows or obstructs the sinus ostia, reducing normal ventilation and drainage of the affected sinus.

Impaired clearance

Obstruction and impaired mucociliary function allow secretions to accumulate within the sinus rather than being cleared normally.

Bacterial infection

The obstructed, poorly draining sinus creates conditions that allow bacteria to proliferate, producing acute bacterial sinusitis.

Core Mechanism

The problem begins with impaired drainage

Acute bacterial sinusitis is usually not a completely separate illness appearing out of nowhere. A viral URI produces mucosal inflammation and edema, which can obstruct the sinus ostia and interfere with normal mucociliary clearance. Secondary bacterial infection can then develop within the poorly draining sinus.

Common Pathogens

Think pneumococcus, H. influenzae, and Moraxella

The major bacterial pathogens associated with pediatric acute bacterial sinusitis are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.

Clinical Translation

This is why the trajectory matters

Most viral URIs cause transient mucosal inflammation and then improve. Acute bacterial sinusitis becomes more likely when symptoms fail to follow that expected recovery pattern—remaining persistent without improvement, beginning with an unusually severe presentation, or worsening after initial improvement.

History & Physical

The diagnosis is in the timeline

Acute bacterial sinusitis is primarily a clinical diagnosis. Focus on how symptoms began, how long they have lasted, and whether the child is improving or worsening.

Diagnostic Framework

Recognize one of three characteristic patterns

Pediatric acute bacterial sinusitis is diagnosed clinically when a child with upper respiratory symptoms develops a persistent illness, severe onset, or worsening course.

1. Persistent Illness

>10 days without improvement

Nasal discharge of any quality, daytime cough, or both persist for more than 10 days without appreciable improvement.

The key is not simply reaching day 10—it is reaching day 10 without a meaningful trend toward improvement.

2. Severe Onset

≥39°C + purulent discharge

High fever of at least 39°C (102.2°F) occurs together with purulent nasal discharge for at least 3 consecutive days at the beginning of the illness.

Fever and purulent discharge must occur together—the combination and duration distinguish this pattern from an uncomplicated viral URI.

3. Worsening Course

Improve → then worsen

A child with an apparent viral URI begins to improve and then develops substantial worsening of nasal discharge, nasal congestion, or daytime cough, or develops a new fever.

This biphasic pattern is often called “double sickening.”

Common Trap

Green mucus does not equal bacterial sinusitis

Nasal discharge commonly becomes thicker, colored, or purulent during an uncomplicated viral URI before becoming clear again or resolving. Purulence alone therefore does not distinguish a viral URI from acute bacterial sinusitis.

Symptoms to Ask About

• Duration and trajectory of nasal symptoms
• Nasal congestion or obstruction
• Nasal discharge of any quality
• Daytime cough, which may worsen at night
• Fever and when it occurred during the illness
• Initial improvement followed by worsening
• Headache or facial discomfort
• Decreased appetite, fatigue, or halitosis

Physical Examination

• General appearance and vital signs
• Nasal discharge and congestion
• Nasal mucosal or turbinate swelling
• Periorbital swelling or erythema
• Extraocular movements and ocular pain
• Visual changes or proptosis
• Facial or forehead swelling
• Neurologic status when complications are suspected

Physical Exam

There is no single exam finding that confirms uncomplicated ABS

Nasal turbinate erythema and swelling are nonspecific. Sinus percussion is not useful, and sinus transillumination is unreliable in children. History—especially the duration and trajectory of symptoms—usually carries more diagnostic weight than the nasal examination.

Red Flags

Look beyond uncomplicated sinusitis

Proptosis, painful or restricted extraocular movements, visual changes, marked periorbital swelling, severe headache, forehead swelling, vomiting, altered mental status, focal neurologic findings, or other concerning findings should raise suspicion for orbital or intracranial extension.

Differential Diagnosis

Not every prolonged runny nose is sinusitis

Many common pediatric conditions produce nasal discharge and cough. Distinguish them by the symptom trajectory, associated findings, and whether the illness fits one of the characteristic patterns of acute bacterial sinusitis.

Viral Upper Respiratory Infection

The most important mimic. Viral URIs commonly cause nasal congestion, cough, fever, and even thick or purulent nasal discharge.

Symptoms generally begin improving within about 10 days. Acute bacterial sinusitis becomes more likely when symptoms persist without improvement, are severe from the onset, or worsen after initial improvement.

Allergic Rhinitis

Consider allergic rhinitis when symptoms are recurrent or chronic and include sneezing, nasal itching, clear rhinorrhea, or other features of atopy.

The characteristic persistent, severe, or worsening illness pattern of acute bacterial sinusitis is usually absent.

Nasal Foreign Body

Particularly important in younger children. A retained nasal foreign body classically produces persistent, unilateral, foul-smelling or purulent nasal discharge.

Unilateral symptoms should prompt careful examination of the nasal cavity rather than automatically attributing the discharge to sinusitis.

Adenoiditis / Adenoid Hypertrophy

Adenoid disease can produce nasal obstruction, persistent nasal discharge, mouth breathing, snoring, and cough, substantially overlapping with symptoms of sinusitis.

Chronic or recurrent symptoms without a characteristic acute sinusitis trajectory should raise consideration of adenoid disease.

Pertussis

Consider pertussis when cough becomes the dominant feature, particularly with prolonged paroxysms, inspiratory whoop, post-tussive emesis, or known exposure.

The respiratory history may begin with nonspecific upper respiratory symptoms before the characteristic cough develops.

Lower Respiratory Infection

Pneumonia or bronchiolitis can also produce cough and fever. Tachypnea, hypoxemia, increased work of breathing, focal lung findings, or prominent lower respiratory symptoms should shift attention below the upper airway.

Clinical Shortcut

Start by asking one question

“How has this illness behaved over time?” A child who is steadily improving still fits a viral URI. A child with symptoms lasting more than 10 days without improvement, severe symptoms from the onset, or improvement followed by substantial worsening fits the characteristic clinical patterns of acute bacterial sinusitis.

Diagnostic Workup

Uncomplicated sinusitis is a clinical diagnosis

Most children with acute bacterial sinusitis do not need laboratory testing, cultures, or imaging. Diagnostic testing becomes important when complications or an alternative diagnosis are suspected.

Uncomplicated ABS

The history usually makes the diagnosis

When a child meets one of the characteristic clinical patterns of acute bacterial sinusitis and has no findings concerning for extension, the diagnosis is clinical. Routine laboratory testing or imaging is not necessary.

Laboratory Testing

Not routinely indicated.

CBC, inflammatory markers, and other routine laboratory studies are generally unnecessary for uncomplicated acute bacterial sinusitis.

Cultures

Do not routinely obtain nasal cultures.

Cultures of nasal secretions do not reliably identify the organisms causing infection within the paranasal sinuses and are not recommended for routine diagnosis.

Imaging

Do not image uncomplicated ABS.

Plain radiographs, ultrasound, CT, and MRI should not be used simply to distinguish acute bacterial sinusitis from an uncomplicated viral URI.

Why Not Image?

Abnormal sinuses do not necessarily mean bacterial sinusitis

Mucosal thickening, opacification, and other sinus abnormalities can occur during an uncomplicated viral upper respiratory infection. Imaging abnormalities therefore cannot reliably distinguish viral inflammation from acute bacterial sinusitis.

Suspected Extension

Orbital or intracranial findings change the workup

Obtain urgent advanced imaging when the examination raises concern for orbital or intracranial complications.

Concern for orbital extension

• Proptosis
• Painful or restricted extraocular movements
• Visual changes
• Significant periorbital swelling or chemosis

Concern for intracranial extension

• Severe or progressive headache
• Vomiting
• Altered mental status
• Focal neurologic findings
• Seizure
• Forehead swelling or tenderness

Advanced Imaging

Use contrast-enhanced CT and/or MRI when complications are suspected

Contrast-enhanced CT can rapidly evaluate the paranasal sinuses, orbit, and surrounding structures. MRI provides greater soft-tissue detail and is particularly useful when intracranial extension is suspected. Imaging choice should be guided by the suspected complication and clinical urgency.

Management

Treat based on the clinical pattern

Management depends on whether the child has persistent illness, severe onset, or a worsening course—and on the risk for resistant organisms or complications.

Persistent Illness

Antibiotics OR brief observation

For symptoms lasting more than 10 days without improvement, either begin antibiotic therapy or observe for up to 3 additional days if the child is otherwise well and reliable follow-up is available.

Start antibiotics if the child worsens at any time or fails to improve during the observation period.

Severe Onset

Start antibiotics

Children with fever ≥39°C (102.2°F) and purulent nasal discharge for at least 3 consecutive days at the beginning of illness should receive antibiotic therapy rather than observation.

Worsening Course

Start antibiotics

Children who initially improve from an apparent viral URI and then substantially worsen or develop a new fever should receive antibiotic therapy.

First-Line Therapy

Amoxicillin with or without clavulanate

Amoxicillin, with or without clavulanate, is first-line therapy for uncomplicated pediatric acute bacterial sinusitis. Selection depends on illness severity and the child's risk for organisms resistant to standard therapy.

Standard-Dose Amoxicillin-Clavulanate

45 mg/kg/day

Dose according to the amoxicillin component, divided twice daily.

Maximum amoxicillin component: 1.75 g/day.

Appropriate for many children with uncomplicated ABS who do not have risk factors for resistant organisms.

High-Dose Amoxicillin-Clavulanate

90 mg/kg/day

Dose according to the amoxicillin component, divided twice daily.

Maximum amoxicillin component: 4 g/day.

Use for severe disease or when there is increased risk for resistant organisms.

Resistance Risk

When should you consider high-dose therapy?

Risk factors described by the AAP include age younger than 2 years, daycare attendance, antibiotic exposure within the previous month, recent hospitalization, incomplete pneumococcal immunization, immunodeficiency, and communities with a high prevalence of resistant organisms.

When is amoxicillin alone reasonable?

Amoxicillin alone may be considered for mild, uncomplicated disease when the child has no risk factors for resistant organisms and local prevalence of β-lactamase–producing respiratory pathogens is low.

Amoxicillin-clavulanate provides additional activity against β-lactamase–producing organisms such as H. influenzae and M. catarrhalis.

Reassessment

Expect improvement within 48–72 hours

Reassess the diagnosis and treatment plan if symptoms worsen or fail to improve within approximately 48–72 hours after starting therapy. Consider an alternative diagnosis, resistant pathogen, inadequate treatment, or a developing complication.

Supportive Care

• Maintain adequate hydration
• Acetaminophen or ibuprofen for pain and fever when appropriate
• Saline nasal irrigation may provide symptomatic relief

Not Routinely Recommended

• Routine antihistamines for uncomplicated ABS
• Routine oral or topical decongestants
• Routine mucolytics

Evidence supporting these adjunctive therapies in uncomplicated pediatric ABS is limited.

Complications

When infection escapes the sinuses

Most children recover without complication, but extension beyond the paranasal sinuses can threaten vision, neurologic function, and life.

Anatomic Spread

Think orbit and brain

The paranasal sinuses lie immediately adjacent to the orbit and intracranial structures. Orbital complications are most often associated with ethmoid sinusitis, while intracranial complications are particularly associated with frontal sinusitis.

Orbital Complications

Orbital involvement is the most common serious complication of acute bacterial sinusitis and commonly results from extension of ethmoid sinus infection.

• Preseptal / periorbital inflammation
• Orbital cellulitis
• Subperiosteal abscess
• Orbital abscess

Worry about postseptal disease when there is:

• Proptosis
• Pain with extraocular movements
• Restricted extraocular movements
• Chemosis
• Decreased visual acuity

Intracranial Complications

Intracranial extension is less common than orbital disease but carries greater potential morbidity. It is particularly associated with frontal sinusitis.

• Epidural empyema
• Subdural empyema
• Brain abscess
• Meningitis
• Intracranial venous thrombosis

Red flags include:

• Severe or progressive headache
• Vomiting
• Altered mental status
• Seizure
• Focal neurologic findings

Pott Puffy Tumor

Frontal bone osteomyelitis + subperiosteal abscess

Despite the name, this is not a tumor. Extension of frontal sinus infection can produce osteomyelitis of the frontal bone with a subperiosteal abscess.

Suspect it in a child or adolescent with forehead swelling and tenderness in the setting of sinusitis.

Cavernous Sinus Thrombosis

Infection spreads into the cavernous sinus

Infection can reach the cavernous sinus through venous pathways or direct spread, including from sphenoid sinusitis.

Cranial nerve dysfunction can develop; the AAP material highlights lateral gaze paralysis as an early finding.

Clinical Pearl

A swollen eye is not automatically simple periorbital cellulitis

Eyelid erythema and swelling may accompany sinusitis, but proptosis, impaired vision, chemosis, or painful or restricted extraocular movements should raise concern for postseptal orbital involvement and prompt urgent evaluation.

Emergency Escalation

Complicated sinusitis requires hospital-level care

Suspected orbital or intracranial extension warrants urgent contrast-enhanced CT and/or MRI, parenteral antimicrobial therapy, and appropriate specialist consultation. Intracranial suppurative disease may also require neurosurgical drainage, while sinus or orbital disease may require ENT or ophthalmologic intervention.

Disposition

Most children can be managed at home

Disposition depends on clinical appearance, ability to tolerate outpatient therapy, reliability of follow-up, and whether there is concern for extension beyond the sinuses.

Outpatient Management

Appropriate for most uncomplicated ABS

• Well-appearing and clinically stable
• No orbital or neurologic red flags
• Able to tolerate oral therapy and maintain hydration
• Reliable caregiver follow-up

Children treated with antibiotics should have clear return precautions and be reassessed if symptoms worsen or fail to improve within approximately 48–72 hours.

Hospital Evaluation / Admission

Escalate when disease may extend beyond the sinuses

• Suspected orbital complication
• Suspected intracranial complication
• Toxic or significantly ill appearance
• Inability to tolerate appropriate outpatient therapy
• Clinical deterioration despite treatment

Complicated disease requires hospital-level evaluation, parenteral antibiotics, advanced imaging, and appropriate specialist consultation.

Observation Option

Observation requires reliable follow-up

For a well-appearing child with persistent illness, an additional 3 days of outpatient observation may be considered instead of immediately starting antibiotics. Begin antibiotic therapy if the child worsens at any time or fails to improve during that observation period.

Return Precautions

Know the findings that should trigger urgent reevaluation

Families should seek prompt reevaluation for worsening illness, severe or progressive headache, persistent vomiting, forehead swelling, increasing periorbital swelling, eye pain, painful or restricted eye movements, proptosis, visual changes, altered mental status, seizure, or other new neurologic symptoms.

Reassessment

No improvement by 48–72 hours? Reconsider the plan.

Failure to improve or clinical worsening after starting therapy should prompt reassessment of the diagnosis and treatment strategy, including consideration of resistant organisms, an alternative diagnosis, or a developing complication.

Clinical Pearls

What should you remember on your next shift?

High-yield principles for recognizing and managing acute bacterial sinusitis in children.

The diagnosis is in the timeline

Do not diagnose acute bacterial sinusitis simply because a child has cough, congestion, or purulent nasal discharge. Look for one of three characteristic patterns: persistent illness, severe onset, or worsening course.

Day 10 is not a magic cutoff

Persistent illness means nasal discharge and/or daytime cough lasting more than 10 days without appreciable improvement. A child who still has mild symptoms on day 10 but is clearly improving may still be following the expected course of a viral URI.

Green mucus does not equal bacterial infection

Thick or purulent nasal secretions can occur during an uncomplicated viral URI. The trajectory of illness is more useful than the color of the nasal discharge for distinguishing viral URI from acute bacterial sinusitis.

Do not image uncomplicated sinusitis

Abnormal sinus findings can occur during viral respiratory infections, so imaging cannot reliably distinguish viral URI from acute bacterial sinusitis. Reserve advanced imaging for concern about orbital or intracranial extension.

The anatomy predicts the complication

Think ethmoid sinus → orbit and frontal sinus → intracranial space. Proptosis, painful or restricted extraocular movements, visual changes, severe headache, neurologic abnormalities, or forehead swelling should immediately raise concern for complicated disease.

Persistent disease is the observation exception

Children with severe onset or worsening-course ABS should receive antibiotics. A well-appearing child with persistent illness may instead undergo an additional 3 days of observation when reliable follow-up and a rescue treatment plan are available.

Progressive Quiz

Can you recognize and manage acute bacterial sinusitis?

Work through increasingly clinical scenarios that test diagnosis, workup, treatment, and recognition of complications.

Question 1

A 6-year-old has had nasal congestion and daytime cough for 12 days. The symptoms remain essentially unchanged without meaningful improvement. Which clinical pattern of acute bacterial sinusitis does this represent?

Anki Deck

Acute Bacterial Sinusitis Anki Deck

Reinforce the highest-yield concepts from this module with 18 spaced-repetition cards.

Download Anki Deck

Requires Anki. Deck content is intended for educational review and should be used alongside the full PediAtlas module.

Evidence Base

Clinical References

Sinusitis (AAP Pediatric Care Online)

AAP clinical reference for pediatric acute bacterial sinusitis, including diagnostic criteria, antibiotic management, imaging indications, and recognition of orbital and intracranial complications.

Acute Bacterial Sinusitis in Children: An Updated Review

Comprehensive review of pediatric sinus development, pathophysiology, microbiology, clinical presentation, diagnosis, treatment, and complications.

Sinusitis (Nelson Textbook of Pediatrics)

Core pediatric reference for paranasal sinus anatomy and development, pathogenesis, microbiology, clinical diagnosis, treatment, and complications.

Educational Disclaimer

PediAtlas is intended for medical education and should not replace institutional guidelines, local protocols, patient-specific assessment, or clinical judgment.