The Pons Flashcards
What part embryonic development is the pons derived from?
The metencephalon (that is derived from the rhombencephalon), alongside the cerebellum.
It is the largest part of the brainstem.
Where is the pons located?
In the anterior part of the posterior cranial fossa.
It is located between the midbrain and the medulla.
What is the bulge formed by in the anterior surface of the midbrain?
What is the groove that runs down the centre of the pons, anteriorly?
The transverse pontocerebellar fibers. They wrap around the otherwise verically oriented brainstem.
The basilar groove.
What cranial nerves are located at the pontomedullary junction?
CN V - Trigeminal - originates from the lateral aspect of the midpons.
CN VI - Abducens - originates at the pontomedullary junction, close to the midline.
CN VII - Facial - originates at the cerebellopontine angle, the more lateral aspect of the pontomedullary junction.
CN VIII - Vestibulocochlear - originates laterally to the facial nerve.
On the posterior aspect of the pons, what structure is nearby?
What other is revealed upon, removing the answer in the question above?
The cerebellum - it is connected to the pons by the middle cerebellar peduncles.
In removing the cerebellum, it will reveal the 4th venticle lying beneath it.
What is the floor of the 4th ventricle composed of?
The dorsal surface of the pons and the medulla.
What are some other important anatomical landmarks of the pons, posteriorly?
1) Medial eminence - marks the midline of the floor.
2) Facial colliculus - a bulging of formed by the fibers of the facial nerve looping around the abducens nucleus - located inferior to medial eminence.
3) Stria medullaris - of the 4th ventricle is a bundle of nerve fibers crossing transversely from the lateral aspect into the midline. They mark the posterior border between the pons and the medulla.
What is the cerebellopontine angle?
What structures are found here?
This is the junction between the pons, medulla and cerebellum.
The cerebellar flocculus, ventricular choroid plexus, and the emerging CNs VII and VIII surround the lateral apertures of the fourth ventricle (the foramen of Luschka).
What is the arterial supply to the pons?
Supplied by the:
1) Pontine arteries (a branch of the basilar artery).
2) Anterior inferior cerebellar + superior cerebellar artery (AICA and SCA).
What is the venous drainage of the pons?
1) Anterior pontomesencephalic bein that drains into the basal vein, which drains into the cerebral veins.
Inferiorly, the pons drains into the inferior petrosal sinus, which drains into the interal jugular foramen.
Clinical relevance: cerebellopontine angle syndrome
This is often the place of intracranial growth.
Symptoms start with a mild impairment of CN VIII.
Vestibular schwannomas - tumours originate in Schwann cells - these are the most common growth in the area. These are benign and complications arise due to compression of nearby structures.
Associated with slow progression of ipsilateral hearing loss. Vestibular schwannomas account for 80% of these cases but there can other causes from different tumours (e.g. meningiomas) to vascular abnormalities.
More common symptoms - ipsilateral hearing loss and tinnitus - due to compression of CN VIII.
Dysequlibrium, and more rarely vertigo - due to compression of the vestibular component of CN VIII.
Nystagmus (repetitive, uncontrolled movements of the eye - due to compression of the cerebellar flocculus.
Other symptoms - facial paraylsis (compression of CN VII), reduced corneal reflex (CN V and CN VII), Trigeminal palsy, ipsilateral cerebellar signs.
