MCQ – 94408

A newborn presents with underdeveloped mandibles and zygomatic bones, atypical external ear structures, and slanted eye openings. Which pharyngeal arch’s abnormal development is most likely responsible for these features?

Correct Answer � A Explanation

The first pharyngeal arch is crucial in the development of the lower face, including structures such as the mandibles (lower jaw) and the zygomatic bones (cheekbones). Malformations in this arch can result in hypoplasia of these bones, as seen in the newborn.

The first arch also contributes to the formation of the malleus and the incus of the middle ear and the external ear’s development, explaining the malformed external ears and the impact on the facial appearance, including the slanted palpebral fissures.

Defects in the development of this arch can result in a condition called mandibulofacial dysostosis or Treacher-Collins syndrome

Reasons to rule  out other options

Option B – Pharyngeal arch 2: The second pharyngeal arch gives rise to several structures in the head and neck region, including the stapes bone, the styloid process of the temporal bone, and some muscles of facial expression. Abnormal development of this arch can result in abnormalities of the ear and hearing, but not the features described in the scenario.

Option C – Pharyngeal arch 3: Amid the manifold structures in the head and neck region, pharyngeal arch 3 is responsible for contributing to several distinct components.

The aegis of this particular arch involves spawning not only part of the hyoid bone but also an essential muscle known as the stylopharyngeus. Abnormal development of this arch can result in problems with swallowing and speech, but not the features described in the scenario.

Option D – Pharyngeal arch 4: In regards to the pharyngeal arches, structures in the larynx are mostly influenced by both arch 4 and 6. These intricate contributions manifest themselves through a combination of forces from laryngeal muscles as well as cartilages for ideal results.

Abnormal development of these arches can cause problems with speech and breathing, but not the features described in the scenario.