Infundibulum and Hiatus Semilunaris of the Nose

Anatomy Diagram (Lateral Nasal Wall)

Important structures in meatuses - lateral nasal wall showing infundibulum and hiatus semilunaris

Lateral nasal wall anatomy showing the infundibulum, hiatus semilunaris, uncinate process, and bulla ethmoidalis in relation to the turbinates.

Axial CT Scan View

CT scan axial view labeling the infundibulum, hiatus semilunaris, uncinate process, and middle meatus

Axial CT of the paranasal sinuses showing the infundibulum and hiatus semilunaris in relation to the middle turbinate and uncinate process.

Osteomeatal Complex (OMC) - Overview

The OMC is a functional concept, not a single anatomic structure. It represents the final common drainage and ventilation pathway for the ethmoidal, maxillary, and frontal sinuses. Its components include:

Uncinate process
Ethmoidal infundibulum
Hiatus semilunaris
Anterior ethmoidal cells
Ostia of the anterior ethmoid, maxillary, and frontal sinuses

(Cummings Otolaryngology, p. 865)

Hiatus Semilunaris

Feature	Detail
Shape	Two-dimensional, crescent/semilunar-shaped gap
Location	Lateral wall of nasal cavity, in the middle meatus
Anterior boundary	Free posterior margin of the uncinate process
Posterior boundary	Anterior wall of the ethmoid bulla (bulla ethmoidalis)
Communication	Connects the middle meatus (medially) to the ethmoidal infundibulum (laterally)

Key point: The hiatus semilunaris is a 2D slit (a gap, not a 3D space). Surgically, it is the entry point through which a probe is passed to access the infundibulum.

(KJ Lee's Essential Otolaryngology, p. 607; Cummings Otolaryngology, p. 865)

Ethmoidal Infundibulum

Feature	Detail
Shape	Funnel-shaped, three-dimensional space
Location	Lateral to the hiatus semilunaris
Medial wall	Uncinate process
Lateral wall	Lamina papyracea
Posterior wall	Anterior wall of ethmoid bulla
Anterior/superior	Frontal process of maxilla + lacrimal bone

Function: Channels secretions from the anterior ethmoid cells, maxillary sinus (enters at 45-degree angle inferiorly), and sometimes the frontal recess, into the middle meatus via the hiatus semilunaris.

(KJ Lee's Essential Otolaryngology, p. 607)

Drainage Pathway (Mucociliary Flow)

Maxillary sinus ostium
       ↓
Ethmoidal Infundibulum  ← anterior ethmoid cells also drain here
       ↓
Hiatus Semilunaris  (2D slit / gateway)
       ↓
Middle Meatus
       ↓
Nasopharynx → swallowed

The frontal sinus drainage depends on the superior attachment of the uncinate process:

If uncinate attaches to lamina papyracea → frontal sinus drains medial to uncinate directly into middle meatus (does NOT enter infundibulum - forms "recessus terminalis")
If uncinate attaches to skull base or middle turbinate → frontal sinus drains into the superior infundibulum

Uncinate Process - The Key Structure

The uncinate process is a sickle-shaped, sagittally oriented bony structure (3-4 mm wide, 1.5-2 cm long). It is the single most important landmark in this region because:

Its free posterior margin forms the anterior boundary of the hiatus semilunaris
Its medial surface forms the medial wall of the ethmoidal infundibulum
It must be removed (uncinectomy) during FESS to access the infundibulum and maxillary ostium

Clinical Relevance

Chronic rhinosinusitis (CRS): Obstruction at the OMC (infundibulum/hiatus semilunaris) blocks drainage from multiple sinuses simultaneously, explaining why maxillary, frontal, and anterior ethmoid sinusitis often co-exist.
FESS: Surgery begins with medialization of the middle turbinate, identification of the uncinate process, and incision through the hiatus semilunaris to enter the infundibulum.
Anatomic variants (concha bullosa, paradoxical middle turbinate, Haller cells) can narrow the infundibulum and predispose to recurrent sinusitis.

(Cummings Otolaryngology, p. 865; Scott-Brown's Otorhinolaryngology, Vol. 2)

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