Corpora Quadrigemina

Definition and Location

• Superior pair - the superior colliculi (optic tectum)
• Inferior pair - the inferior colliculi

The Two Pairs

1. Superior Colliculi (Visual Centers)

• Receive direct input from the retina via the optic tract (extrageniculate pathway through the brachium of the superior colliculus)
• Also called the optic tectum
• Each contains a retinotopic map of the contralateral visual field
• Key functions:
  • Controls rapid (saccadic) eye movements - electrical stimulation commands a saccade to the corresponding point in space
  • Directs reflex orientation toward visual stimuli
  • Mediates the pupillary light reflex (fibers project to the pretectal nuclei)
  • Receives descending input from the frontal eye fields via cortical projections

2. Inferior Colliculi (Auditory Relay)

• Receive auditory information ascending from the cochlear nuclei and superior olivary complex via the lateral lemniscus
• Key functions:
  • Major relay station for auditory information en route to the medial geniculate nucleus (thalamus) and then auditory cortex
  • Important in sound localization (together with the superior olivary complex)
  • Also interact with the superior colliculi - important for auditory-visual integration and orienting responses
  • Superior cerebellar peduncle fibers (brachium conjunctivum) decussate at the level of the inferior colliculus before ascending to the thalamus

Surrounding Structures (Midbrain Context)

• Localization in Clinical Neurology, 8e

Key Clinical Correlation: Parinaud's Syndrome

1. Impairment of vertical gaze, especially upgaze - due to compression of the dorsal vertical gaze center
2. Light-near dissociation - large, irregular pupils that do not react to light but may react to near-far accommodation; this results from disruption of optic fibers to the Edinger-Westphal nuclei via the posterior commissure, while convergence fibers are relatively spared
3. Eyelid abnormalities - bilateral lid retraction (Collier's sign) or ptosis
4. Impaired convergence and convergence-retraction nystagmus on attempted upgaze

• Pineal region tumors (compressing dorsally)
• Hydrocephalus - dilated suprapineal recess pushes down onto the collicular plate
• Multiple sclerosis or vascular disease of the midbrain/pretectal area
• In children with hydrocephalus: the "setting-sun sign" (eyes deviated downward and inward)
• Neuroanatomy through Clinical Cases, 3rd Ed.; The Wills Eye Manual

Vascular Supply

• Medial branches of the posterior cerebral artery (supply lateral cerebral peduncle, lateral tegmentum, corpora quadrigemina, and pineal gland)
• Also contributions from the superior cerebellar artery and posterior choroidal branches
• Adams and Victor's Principles of Neurology, 12th Ed.

Summary

Corpora Quadrigemina - Veterinary Anatomy (Easy Version)

What is it?

Veterinary Terminology - Important Difference!

In veterinary anatomy, the names are different from human anatomy:

Simple Diagram (Dorsal View of Brainstem)

        ← ROSTRAL (toward nose)

         [Pineal body]
    [Rostral colliculus] [Rostral colliculus]   → VISION
    [Caudal  colliculus] [Caudal  colliculus]   → HEARING

         CAUDAL (toward tail) →

What Do They Do? (Simple)

Rostral Colliculi (Front Pair) = "Eye Reflex Centers"

• Receive input from the eyes (optic tract)
• Control reflex eye movements - like when an animal quickly looks toward something that moved
• Help direct the head/eyes toward a visual stimulus
• Connected to the thalamus via the brachium of the rostral colliculus

Caudal Colliculi (Back Pair) = "Ear Relay Stations"

• Receive input from the ears (auditory pathway via lateral lemniscus)
• Act as a relay station for sound information going up to the thalamus (medial geniculate body) and then to the auditory cortex
• Important for sound localization (which direction did that sound come from?)
• Connected to the thalamus via the brachium of the caudal colliculus
• The commissure of the caudal colliculi connects the two sides

Neighboring Structures (Easy)

• Just above (dorsal): the cerebral aqueduct (connects 3rd and 4th ventricles)
• Just in front: pineal body (epiphysis cerebri) - sits between the thalami and the corpora quadrigemina
• Just below: CN IV (trochlear nerve) exits at the level of the caudal colliculus and decussates in the rostral medullary velum - this is the only cranial nerve to exit from the dorsal surface of the brainstem
• Ventral to them: cerebral peduncles (crura cerebri), substantia nigra, red nucleus

Easy Memory Trick

Clinical Relevance in Vet Practice

• A lesion compressing the dorsal midbrain/tectum (e.g., a brain tumor, hydrocephalus) in animals can cause:
  • Loss of menace response or abnormal pupillary light reflexes (rostral colliculus/pretectal area involvement)
  • Vertical gaze deficits - similar to Parinaud's syndrome in humans
  • Hearing pathway disruption if caudal colliculi are affected
• The corpora quadrigemina are visible as four distinct bumps when you examine the dorsal brainstem of a dissected animal brain (dog, cat, etc.)