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Inferior pharyngeal constrictor muscle

The inferior pharyngeal constrictor is the lowermost and thickest of the three pharyngeal constrictor muscles, forming the muscular wall of the laryngopharynx and the upper esophageal sphincter region. It consists of two anatomically and functionally distinct parts: the thyropharyngeus (upper, oblique fibers) and the cricopharyngeus (lower, horizontal fibers).

The thyropharyngeus contributes to pharyngeal peristalsis, while the cricopharyngeus forms the upper esophageal sphincter (UES), regulating bolus entry into the esophagus and preventing esophageal reflux into the pharynx.

Synonyms

  • Constrictor pharyngis inferior

  • Thyropharyngeus and cricopharyngeus complex

  • Upper esophageal sphincter (cricopharyngeal part)

Origin, Course, and Insertion

Origin:

  • Thyropharyngeus: Oblique line of thyroid cartilage

  • Cricopharyngeus: Lateral arch of cricoid cartilage

Course:

  • Fibers sweep posteriorly and medially, curving around the hypopharynx

  • Cricopharyngeus forms a horizontal muscular band at the esophageal inlet

Insertion:

  • Midline pharyngeal raphe

  • Cricopharyngeus inserts into posterior midline fibers without contributing to the raphe

Relations

  • Superiorly: Middle pharyngeal constrictor

  • Inferiorly: Cervical esophagus

  • Anteriorly: Thyroid cartilage, cricoid cartilage, larynx

  • Posteriorly: Buccopharyngeal fascia and prevertebral muscles

  • Laterally: Recurrent laryngeal nerve, inferior thyroid artery, piriform sinus region

Function

  • Thyropharyngeus:

    • Constricts hypopharynx during swallowing

    • Helps propel bolus toward the esophagus

  • Cricopharyngeus (UES):

    • Tonic contraction prevents air entry into esophagus

    • Relaxes during swallowing to allow bolus passage

    • Prevents reflux of esophageal contents into pharynx

MRI Appearance

T1-weighted images:

  • Muscle exhibits intermediate signal intensity, darker than surrounding fat

  • Cricopharyngeus appears as a well-defined ring-like structure at the esophageal inlet

  • Clear demarcation between mucosa (slightly brighter) and deeper muscle layers

T2-weighted images:

  • Shows intermediate-to-low signal intensity

  • Thyropharyngeus and cricopharyngeus fibers distinguished by thickness and orientation

  • Air in the laryngeal and hypopharyngeal lumen appears bright due to susceptibility

STIR:

  • Normal muscle demonstrates intermediate-to-dark signal intensity

  • Strong fat suppression improves visualization of the posterior pharyngeal wall and parapharyngeal spaces

  • Cricopharyngeus appears as a symmetric, dark muscular band

T1 Fat-Saturated Post-Contrast:

  • Muscle enhances mildly and uniformly

  • Mucosa and submucosa show brighter enhancement than muscle layers

  • Cricopharyngeus enhancement forms a subtle ring at the esophageal inlet

CT Appearance

Non-Contrast CT:

  • Muscle appears as soft-tissue density forming the posterior and lateral walls of the hypopharynx

  • Cricopharyngeus seen as a thickened muscular ring at the upper esophageal sphincter

  • Clear contrast between muscle and surrounding fat planes of the parapharyngeal and retrovisceral spaces

Post-Contrast CT:

  • Displays homogeneous, mild enhancement of the inferior constrictor muscle

  • Hypopharyngeal mucosa enhances more than underlying muscle

  • Esophageal inlet contour and cricopharyngeal thickness well visualized

MRI images

Inferior pharyngeal constrictor muscle mri axial image