Anatom3DPosterior commissure
Commissura posterior · Zadní komisura
Nervous system
Looks like
A small bundle of fibres crossing the midline above the entrance of the cerebral aqueduct, at the back of the third ventricle.
What it does
Connects both sides for the pupil light reflex and vertical eye movements.
Keeping it well
Pressure here (e.g. pineal tumour) causes trouble looking up (Parinaud syndrome). It is a standard imaging landmark (PC).
Related conditions
- Acute liver failure
- ADHD
- African trypanosomiasis (sleeping sickness)
- Alcohol withdrawal and delirium tremens
- Altitude sickness
- Alzheimer's disease
- Amyloidosis (AL and ATTR)
- Autism spectrum disorder
- Bipolar disorder
- Birth asphyxia (hypoxic-ischaemic encephalopathy)
- Body dysmorphic disorder
- Botulism
- Brain abscess
- Brain aneurysm
- Brain tumour (glioma & meningioma)
- Cerebral palsy
- Chickenpox (varicella)
- Chronic insomnia
- Chronic neuropathic pain
- Chronic pain syndrome
- Cluster headache
- Concussion (mild TBI)
- Congenital hypothyroidism
- Cryptococcal meningitis
- Delirium
- Dementia with Lewy bodies
- Down syndrome (trisomy 21)
- Drowning
- Eating disorders
- Encephalitis
- Epilepsy
- Essential tremor & dystonia
- Fainting (syncope)
- Febrile seizures
- Fibromyalgia
- Fragile X syndrome
- Frailty & falls in older age
- Functional (somatic) symptom disorder
- Generalised anxiety disorder
- Guillain-Barré syndrome
- Haemorrhagic stroke
- Heat exhaustion & heatstroke
- Hepatic encephalopathy
- Huntington's disease
- Hydrocephalus
- Hypoglycaemia (low blood sugar)
- Intellectual disability
- Ischaemic stroke
- Japanese encephalitis
- Lead poisoning
- Long COVID (post-viral syndrome)
- Lyme disease
- Major depressive disorder
- ME/chronic fatigue syndrome
- Measles
- Medication-overuse headache
- Meningitis
- Migraine
- Multiple sclerosis
- Myasthenia gravis
- Narcolepsy
- Neurocysticercosis
- Normal pressure hydrocephalus
- Parkinson's disease
- Peripheral neuropathy
- Phenylketonuria (PKU)
- Poisoning & overdose
- Post-traumatic stress disorder
- Postnatal depression
- Postpartum psychosis
- Rabies
- Restless legs syndrome
- Roseola (sixth disease)
- Schizophrenia
- Self-harm and suicidal crisis
- Shingles (herpes zoster)
- Subdural haematoma
- Substance use disorder
- Tension-type headache
- Tetanus
- Thrombotic thrombocytopenic purpura (TTP)
- Tick-borne encephalitis
- Tics and Tourette syndrome
- Toxoplasmosis & CMV
- Transient ischaemic attack
- Traumatic brain injury (moderate to severe)
- Tuberous sclerosis complex
- Vascular dementia
- Vitamin B1, C and other deficiencies