If the fetal head is deflexed, what anatomical feature cannot be palpated during an internal exam?

When the fetal head is deflexed, it means that the chin is not tucked towards the chest, which can affect the positioning of the fetal skull during an internal examination. In this position, the posterior fontanelle, located at the junction of the parietal and occipital bones, is not positioned optimally for palpation.

The posterior fontanelle is smaller and covered by soft tissue compared to the anterior fontanelle, which is larger and more readily accessible for palpation during a vaginal examination. When the head is deflexed, the occipital bone is more prominent and easier to feel, and the parietal bone can also be palpated as the head's position changes. Therefore, while the anterior fontanelle and the occipital bone can still be accessed during the exam, the posterior fontanelle remains less accessible due to its position during deflexion.

This understanding emphasizes the importance of fetal positioning in determining what anatomical structures can be palpated during labor examinations, highlighting variations in clinical assessments based on fetal head flexion or deflexion.