Middle Meatal Antrostomy

Definition & Rationale

• Mucociliary clearance within the maxillary sinus always converges toward the natural ostium, regardless of where an antrostomy is created. This is why preserving and incorporating the natural ostium is non-negotiable.
• The natural ostium opens at a 45° angle in the floor of the ethmoidal infundibulum, anteriorly positioned and best visualized only after removal of the uncinate process.

Prerequisite: Uncinectomy

1. A ball-tipped probe is slid into the infundibulum behind the posterior free edge of the uncinate to medialize it off the lamina papyracea (reduces orbital penetration risk).
2. A pediatric backbiter punch retrogradely incises the uncinate at the junction of the upper 2/3 and lower 1/3 — this level corresponds to the natural maxillary ostium and minimizes orbital risk.
3. The incision extends anteriorly until the harder lacrimal bone (anterior maxillary line) is reached — do not penetrate this bone (nasolacrimal duct injury risk).
4. The superior third of the uncinate may be preserved temporarily to protect frontal recess.

Identifying the Natural Ostium

• Angled endoscopes (30°, 45°, or 70°) are critical — the natural ostium cannot be adequately seen with a 0° scope.
• The ostium is elliptical, located in the floor of the infundibulum lateral to the lower third of the uncinate.
• Accessory ostia are circular and usually in the posterior fontanelle — they must NOT be confused with the natural ostium.
• If edema obscures the ostium: follow the "mucus trail" with a small curved suction; gently probe with a maxillary sinus seeker directed inferolaterally (never directly lateral — orbital injury risk).

Performing the Antrostomy

1. A double-ball probe (or maxillary sinus seeker) is used to gently probe and dilate the natural ostium posteriorly — avoid its sharp anterior aspect to prevent circumferential scarring and stenosis.
2. Do not bite anteriorly into the ostium — nasolacrimal duct injury risk.
3. A straight punch can transect mucosa between medial and superior sinus walls to minimize mucosal stripping.
4. Enlarge posteriorly using back-biting instruments and 90°-angled graspers (through-cutting instruments).
5. Enlarge inferiorly/superiorly with side-biting antrum punches; a down-biter is useful inferiorly (avoid injuring inferior turbinate).
6. Do not strip mucosa — leads to submucosal hematoma, delayed healing, and scarring/mucociliary dysfunction.
7. Any accessory ostia present must be incorporated into the antrostomy to prevent mucus recirculation.

Size of Antrostomy

• Standard antrostomy for straightforward CRS.
• Mega-antrostomy (maxillary mega-antrostomy): includes partial inferior turbinectomy, widening to the nasal cavity floor — indicated when mucociliary clearance is ineffective.
• Larger antrostomies are favored in CRS with nasal polyps (CRSwNP) or significant mucociliary impairment, to optimize topical drug delivery.

Extended Maxillary Sinus Procedures (Spectrum)

Common Causes of Failure

• Failure to incorporate the natural ostium into the MMA → mucus recirculation
• Maxillary ostium stenosis
• Lateralization of the middle turbinate
• Residual ethmoidal air cells
• Frontal recess scarring and adhesions

Post-Antrostomy Examination

• Medial and inferior orbital wall
• Infraorbital nerve (watch for infraorbital cell blocking from above)
• Any pus or debris → culture

Complications / Risks

• K.J. Lee's Essential Otolaryngology, pp. 616–617
• Cummings Otolaryngology: Head and Neck Surgery, pp. 882–884