Odontogenic sinusitis is maxillary sinusitis originating from dental pathologies and is responsible for 10-40% of all maxillary sinusitis cases. The most common causes are periapical abscess, periodontal disease, and dental implant complications. The roots of upper premolar and molar teeth show close proximity to the maxillary sinus floor or directly protrude into the sinus; this anatomic proximity facilitates the spread of infection to the sinus. Oroantral fistula, material pushed into the sinus during root canal treatment, or dental extraction complications can also lead to odontogenic sinusitis. Clinically, the combination of unilateral maxillary sinusitis, foul odor, and dental symptoms is characteristic. On CT, ipsilateral maxillary sinus opacification with concurrent alveolar bone pathology confirms the diagnosis.
Age Range
20-70
Peak Age
45
Gender
Equal
Prevalence
Common
Odontogenic sinusitis arises from the close anatomic relationship of upper jaw tooth roots with the maxillary sinus floor. The roots of upper first and second molar teeth are in closest proximity to the sinus floor, and in a significant proportion of cases, roots penetrate the Schneiderian membrane and directly protrude into the sinus lumen. Following periapical infection, periodontal disease, or dental procedure complications, bacteria cross the Schneiderian membrane (sinus mucosa) to reach the sinus lumen. Anaerobic and polymicrobial flora predominate in odontogenic infections, causing standard sinusitis treatment to be inadequate. The inflammatory process leads to mucosal thickening, fluid accumulation, and osteitis; when chronic, sinus wall sclerosis, mucosal polypoid changes, and oroantral fistula may develop. On imaging, unilateral sinus opacification concurrent with periapical radiolucency reflects this pathogenetic mechanism.
Unilateral maxillary sinus opacification with concurrent periapical radiolucency at the ipsilateral upper tooth root and/or focal bone defect at the sinus floor on coronal CT — pathognomonic imaging finding of odontogenic sinusitis, distinguishing from rhinogenic sinusitis (usually bilateral or OMC-related).
The cardinal CT finding of odontogenic sinusitis is unilateral maxillary sinus opacification seen concurrently with alveolar bone/dental pathology. Sinus opacification may be complete or partial; mucosal thickening, air-fluid level, or polypoid changes may accompany. Periapical radiolucency (granuloma/abscess), periodontal bone destruction, or root fracture is detected at the responsible tooth. Focal bone defect or cortical loss at the sinus floor shows the pathway of infection spread. The contralateral sinus is usually clear or shows minimal mucosal thickening — this asymmetry strongly suggests odontogenic etiology. In the presence of dental implant, implant protrusion into the sinus and surrounding inflammatory changes are evaluated.
Report Sentence
Opacification is observed in the left/right maxillary sinus with periapical radiolucency at the ipsilateral upper molar/premolar tooth root and focal bone defect at the sinus floor; findings are compatible with odontogenic sinusitis.
Oroantral fistula is an abnormal communication between the oral cavity and maxillary sinus, appearing as a defect in the alveolar bone and sinus floor on CT. It most commonly develops after upper molar tooth extraction; sinus floor perforation occurs particularly during extraction of roots close to or protruding into the sinus. On CT, loss of bone cortex continuity at the defect site and reactive bone thickening surrounding the defect are observed. In chronic oroantral fistula, polypoid mucosal changes and granulation tissue develop around the defect. The size, location of the defect, and status of surrounding tissues are critical for surgical repair planning. Coronal CT reformations best demonstrate the fistula tract.
Report Sentence
A defect is observed in the alveolar bone and maxillary sinus floor at the left/right upper molar/premolar region, compatible with oroantral fistula.
On contrast-enhanced CT, periapical abscess appears as a peripherally enhancing hypodense collection around the tooth root. When the abscess crosses the maxillary sinus floor extending into the sinus, focal destruction at the sinus floor and intense enhancement of the sinus mucosa are seen. Osteitis (increased density and thickening) in surrounding alveolar bone and soft tissue inflammatory changes (fat stranding, cellulitis) may accompany. In complicated cases, the abscess may extend to the buccal or palatal space. In subperiosteal abscess formation, periosteal elevation and subperiosteal collection are clearly visible on contrast-enhanced CT. Inflammation around dental implants (peri-implantitis) gives similar imaging findings.
Report Sentence
A peripherally enhancing hypodense collection (periapical abscess) is observed around the upper molar/premolar tooth root, extending into the ipsilateral maxillary sinus through a focal defect in the sinus floor.
On MRI, odontogenic sinusitis shows characteristic findings on T2-weighted sequences. Intrasinus fluid accumulation appears T2 hyperintense; however, proteinaceous or hemorrhagic content may alter the signal. Mucosal thickening appears as a T2 hyperintense peripheral rim. Periapical abscess appears on T2 as hyperintense center (fluid/pus) with surrounding hypointense rim (fibrous capsule). Periapical inflammation shows markedly hyperintense signal on T2 STIR — bone marrow edema is sensitively detected. Bone defect at the sinus floor may not be as clearly visible on MRI as on CT, but mucosal-periosteal discontinuity provides a clue. MRI superiority lies in evaluating the extent of inflammatory changes and soft tissue involvement.
Report Sentence
T2 hyperintense fluid retention and mucosal thickening are observed in the left/right maxillary sinus with increased signal intensity on T2 STIR around the ipsilateral upper tooth root (periapical inflammation).
In dental implant-associated odontogenic sinusitis, CT shows the implant body crossing the maxillary sinus floor and protruding into the sinus lumen. Peri-implant radiolucency (bone loss), sinus membrane elevation, and reactive mucosal thickening are seen around the implant. Focal opacification and/or air-fluid level are present around the intrasinus portion of the implant. After sinus lift (augmentation) surgery, graft material appears as hyperdense granular material at the sinus floor, and surrounding opacification develops in graft infection. A radiolucent line at the bone-implant interface around the implant indicates osseointegration loss (failure). Metal artifact reduction (MAR) techniques improve soft tissue evaluation around the implant.
Report Sentence
Dental implant body in the left/right upper jaw crosses the maxillary sinus floor and protrudes into the sinus lumen with surrounding mucosal thickening and peri-implant radiolucency.
Ultrasonography is a limited but useful modality for maxillary sinus evaluation in certain situations. The normal air-filled sinus shows strong reflection from the anterior wall (A-line artifact) on ultrasonography and intrasinus structures cannot be evaluated. However, when the sinus is filled with fluid, ultrasound is transmitted through the fluid and the posterior sinus wall becomes visible (positive sinusogram). In odontogenic sinusitis, fluid accumulation in the ipsilateral maxillary sinus appears as anechoic or hypoechoic collection. Mucosal thickening may appear as a hypoechoic band along the anterior sinus wall. When air-fluid level is present, intense reflection (reverberation artifact) occurs at the air-fluid interface. Ultrasonography provides rapid radiation-free assessment in children and pregnant women.
Report Sentence
Positive sinusogram on ultrasonography of the left/right maxillary sinus with anechoic/hypoechoic collection compatible with intrasinus fluid accumulation.
Foreign bodies pushed into the maxillary sinus after dental procedures appear as high-density structures on CT. The most commonly displaced materials into the sinus are root canal filling material (gutta percha — hyperdense tubular structure), broken instrument fragments (metallic hyperdense), dental implant parts, and root fragments. Reactive mucosal thickening, granulation tissue, and in chronic cases fungus ball (aspergilloma) may develop around the foreign body — metallic foreign bodies have increased risk of fungal colonization. On coronal CT, the location of the foreign body (sinus floor, lateral wall, proximity to ostium) and surrounding sinus pathology are evaluated together. The size, shape, and intrasinus position of the foreign body are critical for surgical removal planning.
Report Sentence
A hyperdense foreign body (dental material/root fragment) is observed at the floor/lumen of the left/right maxillary sinus with surrounding reactive mucosal thickening.
Criteria
Periapical radiolucency (granuloma/abscess) at the tooth root apex with extension to the sinus floor. Most common cause, seen in upper first and second molar teeth.
Distinct Features
Round radiolucency at tooth root apex on CT, focal destruction at sinus floor, ipsilateral sinus mucosal thickening. Dental caries or restoration is usually present in the tooth.
Criteria
Spread of infection to the sinus through alveolar bone due to advanced periodontal disease (bone loss, periodontal pocket). Unlike periapical lesion, bone loss progresses along the root.
Distinct Features
Vertical or horizontal bone loss along the tooth root on CT, tartar (calculus) accumulation on root surface, furcation involvement. Slower course and associated with chronic sinusitis.
Criteria
Sinus membrane perforation and infection development during or after dental implant placement. Implant crosses the sinus floor and protrudes into the sinus.
Distinct Features
Metallic implant body protrusion into sinus lumen on CT, surrounding peri-implant radiolucency and reactive mucosal thickening. In the presence of sinus lift material, graft infection should be considered.
Criteria
Development of permanent communication (fistula) between oral cavity and maxillary sinus after tooth extraction or trauma. Oral flora continuously enters the sinus through the fistula.
Distinct Features
Alveolar bone defect at extraction site and loss of bone continuity at sinus floor on CT. Risk of chronic sinusitis, polypoid mucosal changes, and fungal superinfection is high. Requires surgical repair (flap closure).
Distinguishing Feature
Rhinogenic acute sinusitis usually shows bilateral or multisinus involvement and is associated with OMC obstruction. Odontogenic sinusitis is characterized by unilateral maxillary sinus involvement and dental pathology. Alveolar bone evaluation is distinguishing.
Distinguishing Feature
Fungus ball also causes unilateral maxillary sinus opacification and may be associated with dental foreign bodies. However, centrally located hyperdense calcifications/metallic opacities (fungal hyphal calcification) within the sinus are characteristic of fungus ball. These calcifications are absent in odontogenic sinusitis — periapical pathology is distinguishing.
Distinguishing Feature
Maxillary sinus SCC also causes unilateral opacification but shows aggressive bone destruction, irregular soft tissue mass, and enhancement. In odontogenic sinusitis, bone changes are reactive (sclerosis, remodeling) and destruction is limited. There is no temporal relationship with dental pathology in SCC. Solid enhancing mass on contrast-enhanced CT suggests SCC.
Distinguishing Feature
Retention cyst is a dome-shaped soft tissue density mass arising from sinus mucosa without accompanying sinusitis findings. In odontogenic sinusitis, sinus opacification is inflammatory (mucosal thickening, fluid) with accompanying dental pathology. Retention cyst is incidental and does not require treatment.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
Post-treatment CT at 4-6 weeks to confirm resolution. Dental follow-up mandatory. Oroantral fistula requires surgical repair.Odontogenic sinusitis requires treatment different from standard sinusitis antibiotic protocols due to its anaerobic and polymicrobial flora. Anaerobic-coverage antibiotics (amoxicillin-clavulanate or clindamycin) should be initiated. Source tooth treatment (root canal therapy, extraction) is mandatory — sinusitis chronifies and recurs without treating the dental source. Oroantral fistula requires surgical repair. In complicated cases (orbital, intracranial extension), emergent surgical drainage is indicated. Antifungal therapy may be needed due to fungal superinfection risk. Treatment response should be evaluated with follow-up CT.
Odontogenic sinusitis accounts for 10-40% of all chronic maxillary sinusitis. It does not respond to standard sinusitis treatment — dental source treatment (extraction, root canal, oroantral fistula repair) is required. Delayed diagnosis leads to chronicity and complications.