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Maxillary sinus

The maxillary sinus is the largest paranasal sinus, located within the body of the maxilla on each side of the nasal cavity. It has a pyramidal shape, with its base forming the lateral wall of the nasal cavity and the apex extending toward the zygomatic process. The sinus is lined by respiratory epithelium (ciliated pseudostratified columnar epithelium) and mucous glands, which help in mucociliary clearance. Its walls are thin and closely related to dental roots, the orbit, and the nasal cavity, making it clinically significant for both dental and ENT evaluation. The maxillary sinus communicates with the nasal cavity through the ostium in the middle meatus, allowing drainage and ventilation.

Synonyms

  • Antrum of Highmore

  • Maxillary antrum

  • Paranasal sinus of maxilla

Function

  • Reduces the weight of the skull

  • Contributes to voice resonance

  • Assists in humidifying and warming inhaled air

  • Provides mucociliary clearance to trap and remove pathogens and debris

  • Plays a role in craniofacial structural support

MRI Appearance

T1-weighted images:

  • Air within the sinus appears as a signal void (black)

  • Normal sinus mucosa is thin and may appear as a low-intensity line along the bony walls

  • Fluid, mucus, or soft tissue lesions appear intermediate to high signal, depending on protein content and chronicity

  • Pathological conditions like cysts, polyps, or tumors may appear iso- to hyperintense relative to muscle

T2-weighted images:

  • Air remains a signal void (black)

  • Fluid or mucosal thickening appears bright hyperintense, making it easy to detect sinusitis, edema, or cysts

  • Thickened mucosa or retained secretions are clearly visible against the hypointense bone and black air

STIR (Short Tau Inversion Recovery):

  • Fat suppression enhances detection of edema, inflammation, or soft tissue lesions

  • Normal sinus air remains signal void, while abnormal tissue appears bright hyperintense, highlighting even subtle pathology

CT Appearance

  • The maxillary sinus appears as a well-defined air-filled cavity, with the air being hypodense (black)

  • Thin bony walls are hyperdense and clearly delineated in axial, coronal, and sagittal planes

  • Mucosal thickening, fluid accumulation, polyps, cysts, or tumors appear as soft tissue density within the air-filled sinus

  • CT is particularly valuable for preoperative assessment, trauma evaluation, chronic sinusitis, and dental-related sinus pathology

MRI images

Maxillary Sinus mri axial image -img-00000-00000

CT image

Maxillary sinus CT

X Ray image

x ray Maxillary sinus