Midbrain Structure and Function

Midbrain and Tectum

• Midbrain, also known as the mesencephalon, is a small region of the brainstem that serves as a relay center for sensory and motor information.
• The midbrain is divided into three main parts: tectum, tegmentum, and cerebral peduncles.

Tectum

• The tectum is a region located in the midbrain, posterior to the cerebral aqueduct of Sylvius, and is primarily responsible for sensory processing, particularly visual and auditory information.
• The tectum is divided into two main subdivisions: superior colliculus and inferior colliculus.

Superior Colliculus

• The superior colliculus is a paired structure located in the midbrain, specifically within the tectum, which is the dorsal portion of the midbrain.
• It is involved in visual processing and the coordination of eye movements, receiving direct visual input from the retina via the optic nerve and optic tract.

Inferior Colliculus

• The inferior colliculus is a paired structure located in the midbrain, below the superior colliculus in the tectum.
• It is divided into several subdivisions, including the central nucleus and external cortex.
• The inferior colliculus is part of the hearing pathway, receiving impulses from the cochlea via the cochlear nerve and ascending to the lateral lemniscus to synapse with the inferior colliculi.

Blood Supply

• The tectum receives blood supply primarily from the superior cerebellar artery and posterior cerebral artery.
• Obstructions in the blood supply to the tectum can lead to significant conditions, including hydrocephalus, which can cause increased intracranial pressure and potentially damaging brain structures.

Clinical Manifestations

• Clinical manifestations of dysfunction in the tectum of the midbrain can include issues with visual and auditory processing, such as visual disturbances, difficulty tracking moving objects, and impaired auditory localization.
• Problems with balance and coordination may also arise due to disruptions in the midbrain's role in spatial orientation and motor control.

Parinaud Syndrome

• Parinaud syndrome, also known as sylvian aqueduct syndrome, is a condition characterized by a triad of impaired upward gaze, convergence retraction nystagmus, and pupillary hyporeflexia.
• The classic triad is seen in about 65% of patients with Parinaud's syndrome.
• The characteristic symptom of Parinaud syndrome is limited conjugate upgaze, due to the involvement of the vertical gaze centers, which are in proximity to the Superior colliculus.
• The causes of Parinaud syndrome include pineal gland tumors and other midbrain pathologies like hemorrhage and infarction.