Antrolith

An antrolith is a calcified body that forms through the progressive accumulation of mineral salts around a central nidus within the maxillary sinus (antrum).[1] The nidus is typically of endogenous origin—tooth or bone fragments, inspissated blood, pus, mucus, or fungal material—though exogenous foreign bodies may also serve as the core.[1][2] Pathogenesis is not fully elucidated but is associated with chronic sinus inflammation, impaired sinus drainage, and the presence of intrasinus foreign material.[1][3] Antroliths are benign, non-neoplastic entities that present radiographically as circumscribed radiopaque masses within the maxillary sinus and are most often discovered incidentally.[4] The majority are asymptomatic and require no treatment; surgical removal is reserved for symptomatic or large lesions.[4][5]

• Antrolith (preferred): Introduced by Bowerman in 1969 to specifically designate a calcified body within the maxillary antrum.[1]
• Maxillary antrolith: Synonymous; used to distinguish from calculi in other paranasal sinuses.
• Sinolith: A broader term encompassing calculi in any paranasal sinus (maxillary, frontal, ethmoid, or sphenoid).[6]
• Rhinolith: Refers specifically to a calcified body within the nasal passage and should not be used interchangeably with antrolith.[1]
• Antral calculus / antral stone / antral rhinolith: Older or informal synonyms occasionally encountered in the literature.[6]

• Prevalence: Reported prevalence varies substantially by population and imaging modality. CBCT-based studies report per-sinus prevalence of approximately 8.4% in a Taiwanese cohort, whereas CT-based surveys and studies from other populations report much lower rates of 0%–3.2%. The higher detection rate on CBCT likely reflects the superior sensitivity of volumetric imaging for small calcifications.[1][3][7]
• Age: Prevalence increases with age, with the highest rates observed in patients older than 49 years, consistent with cumulative sinus irritation over time.[1]
• Sex: One CBCT series found a female predominance (66.7%), though data are limited and sex predilection remains uncertain.[1]
• Anatomic distribution: Predominantly unilateral (82.5%) and solitary (67.5%). The molar region of the maxillary sinus is the most common location (95.0%), with the sinus floor involved in 77.5% of cases, followed by the lateral wall (17.5%) and medial wall (5.0%). Antroliths occur more frequently in dentate areas (60.0%). Involvement of other paranasal sinuses (frontal, ethmoid, sphenoid) is rare.[6][7]

Presentation

Most antroliths are asymptomatic and discovered incidentally on dental or sinus imaging obtained for unrelated reasons.[2][4] When symptoms occur, they are typically attributable to associated chronic sinusitis rather than the antrolith itself.

Symptoms

• Nasal congestion, rhinorrhea, facial pain, and headache may develop when the antrolith is associated with chronic maxillary sinusitis.[3][8]
• Fetid nasal discharge (cacosmia) has been reported occasionally.
• Antrolithiasis should be considered in cases of chronic sinusitis refractory to appropriate medical therapy.[3]

Complications and clinical significance

• Sinus membrane thickening: The sinus membrane tends to encircle antroliths, resulting in significantly increased membrane thickness.[7]
• Implant surgery implications: Large antroliths adjacent to the sinus floor increase the risk of sinus membrane perforation during sinus augmentation procedures and may impede osteotome sinus floor elevation.[1][7]
• Fungal association: Noninvasive aspergillosis (fungus ball) of the maxillary sinus may calcify, and approximately half of reported cases demonstrate calcification of fungal mycelia forming antroliths.[2]

Location and distribution

Antroliths are located within the maxillary sinus, overwhelmingly in the posterior (molar) region (95.0%).[7] They are found most commonly along the sinus floor (77.5%), less often along the lateral wall (17.5%), and rarely along the medial wall (5.0%).[7] Unilateral involvement predominates (82.5%), and most are solitary (67.5%), though multiple antroliths may occur in a single sinus.[7]

On panoramic radiography, an antrolith projects as a radiopaque focus superimposed on the maxillary sinus, typically above the apices of the posterior teeth. Panoramic imaging has limited sensitivity for sinus pathology overall, and small antroliths may be missed.[9] Periapical radiographs may incidentally reveal a radiopaque mass within the sinus if the lesion falls within the field of view.

Periphery and shape

• The outline may be smooth or irregular (rugged).[1]
• Shape is variable: round, oval, or irregular.[1][4]
• Margins are generally well defined and circumscribed, distinguishing the lesion from diffuse calcification patterns.[4]

Internal architecture

• Antroliths are typically radiopaque, reflecting the deposition of calcium salts (predominantly calcium oxalate or calcium phosphate) around the central nidus.[1][3]
• Density is usually homogeneously radiopaque, though heterogeneous patterns with a denser periphery and less dense core may be seen, particularly in larger lesions.
• Rarely, antroliths may appear radiolucent or of low density, presumably when mineralization is incomplete.[1]
• On CBCT, the calcified mass is readily distinguished from surrounding soft-tissue density of the sinus membrane or mucosal thickening. Mean dimensions on CBCT are approximately 5.6 × 4.1 × 3.5 mm (length × width × height), though considerable variation exists (SD 2.1–4.4 mm).[7]

Effects on adjacent structures

• Sinus membrane: The Schneiderian membrane tends to encircle the antrolith progressively, leading to measurable membrane thickening. This thickening is clinically relevant for sinus augmentation planning.[7]
• Teeth: Antroliths do not cause root resorption or displacement of adjacent teeth. They are not attached to the alveolar bone or tooth roots.
• Sinus walls: Bony walls of the maxillary sinus are not remodeled, expanded, or eroded by antroliths. The absence of bony change is an important distinguishing feature from neoplastic processes.

Recognized variants

• Fungal-associated antrolith: When the nidus is a calcified fungal mycetoma (most commonly Aspergillus), the antrolith may be accompanied by partial or complete sinus opacification and an irregular soft-tissue surface. Scattered punctate or flocculent calcifications within an opacified sinus suggest a fungus ball rather than a simple antrolith.[2][10]
• Foreign-body–associated antrolith: Displaced tooth roots, endodontic materials, or other iatrogenic foreign bodies within the sinus may serve as the nidus, and the calcified mass may partially encase recognizable tooth structure or filling material.

Medical CT

On medical CT, antroliths appear as well-circumscribed, hyperdense foci within the maxillary sinus, typically along the sinus floor.[3] CT allows precise localization relative to the sinus walls, ostium, and adjacent structures and is superior to panoramic radiography for confirming the intrasinus location and excluding bony-origin lesions. Associated findings may include mucosal thickening or partial sinus opacification when concurrent sinusitis is present; all three antroliths identified in one CT-based series had associated sinusitis.[3] CT is particularly valuable for differentiating an isolated antrolith from a calcified fungus ball, in which calcification is typically accompanied by partial opacification with an irregular surface and possible bony sclerosis of the sinus walls.[10] Chemical analysis of surgically retrieved antroliths has confirmed calcium oxalate composition.[3]

The differential diagnosis of a circumscribed radiopaque mass within the maxillary sinus includes several entities.[1] The key diagnostic challenge is distinguishing a benign, incidental antrolith from lesions that require biopsy or more aggressive management.

The highest-risk diagnostic pitfall is failing to recognize a calcified fungus ball masquerading as a simple antrolith, as fungal disease may require surgical removal and histopathologic evaluation to exclude mucosal invasion.[2][13] When imaging findings are ambiguous—particularly when calcification is accompanied by sinus opacification—otolaryngologic consultation and surgical retrieval with histopathologic examination are warranted.[1]

Gross and microscopic features

Antroliths are composed of concentric laminations of mineral salts deposited around a central nidus.[1][14] The nidus may consist of:

• Endogenous material: inspissated mucus, blood, pus, desquamated epithelial cells, or bone fragments[1]
• Exogenous material: displaced tooth fragments, endodontic filling material, or other foreign bodies[1][2]
• Fungal elements: calcified Aspergillus mycelia in cases of noninvasive aspergillosis[2]

Chemical composition

Chemical analysis has identified calcium oxalate as a principal mineral component.[3] Proteomic and immunohistochemical studies have demonstrated expression of cross-linking and calcification proteins (BMP2/4, TGFβ1) in the nidus zone, with exfoliated epithelial cells admixed in the peripheral multilayer zone.[14]

Radiologic-pathologic correlation

The concentric lamellar deposition of mineral salts accounts for the well-circumscribed, radiopaque appearance on imaging. Heterogeneous density on CBCT or CT may reflect alternating layers of organic and inorganic material. When a fungal nidus is present, histopathologic examination reveals matted, dense hyphae adjacent to the respiratory mucosa with a chronic nongranulomatous inflammatory response and no mucosal invasion.[2][15]

Asymptomatic antroliths

The majority of antroliths are incidental findings and require no treatment.[4] Observation is appropriate when the lesion is small, asymptomatic, and the imaging appearance is characteristic.

Indications for intervention

• Symptomatic chronic sinusitis refractory to medical therapy in the presence of an antrolith[3]
• Large antroliths that may complicate planned sinus augmentation or implant surgery[1][7]
• Diagnostic uncertainty requiring histopathologic confirmation to exclude fungal disease or neoplasm[1]

Surgical approaches

• Functional endoscopic sinus surgery (FESS): Preferred minimally invasive approach for symptomatic antroliths, providing direct visualization and removal with preservation of sinus physiology.[6][16]
• Caldwell-Luc approach: May be required for large antroliths or when concomitant sinus augmentation is planned. Coupling antrolith removal with intrasinus bone grafting via a Caldwell-Luc approach avoids a second surgery and the complications of operating in a scarred sinus.[5]
• Modified implant placement: When antroliths are encountered during osteotome sinus floor elevation, small lesions can often be elevated with the sinus membrane. For large antroliths that cannot be displaced, drilling through the antrolith to seat the implant has been described with successful outcomes.[1]

Prognosis

Antroliths do not recur after complete removal. There is no malignant potential. When associated sinusitis is the primary clinical problem, resolution of sinus symptoms follows surgical removal and restoration of sinus drainage.[3][6]