Suspect herniation due to an intracranial mass lesion as a cause of fixed dilated pupil in an unconscious patient. A fixed dilated pupil in an awake patient is NOT due to herniation.
CausesPharmacologic blockade is the most common cause of a fixed dilated pupil in an otherwise normal healthy patient.
A single fixed dilated (mydriatic) pupil can be caused by:
Pharmacological blockade– typically topical mydriatic drugs used to facilitate ophthalomological examinations. anticholinergic drugs: e.g. atropine, cyclopentolate and tropicamide alpha1-agonists: phenylephrine. Oculomotor nerve palsy (3rd cranial nerve) parasympathetic nerves are in the superficial parts of the nerve, so tend to be more vulnerable to compressivelesions and spared by vascular lesions (e.g. diabetes mellitus). If an acute third nerve palsy is accompanied by pupillary mydriasis an aneurysm arising from the posterior communicating artery must be excluded.[See a Spider called Willis for an easy way to remember the components of the Circle of Willis and its relations.] Others: Holmes-Adie pupil (tonic phase) post-traumatic iridocyclitis (e.g. direct facial trauma) acute closed-angle glaucoma physiologicalanisocoria ocular prosthesis – the normal pupil may be relatively constricted due to ambient light.
CCC Differential Diagnosis Series
NEURO
Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP
Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS
Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT
Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT
Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK
Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM
Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO
Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM
Splenomegaly
PAEDS
Floppy infant
MISC
Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING
CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR,
ABDO: Gas on abdominal X-ray, Kidney mass,
BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly,
OTHER: Pseudofracture on X-Ray,
LABS
LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,
HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,
ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis,
Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes
[cite]
Critical Care
Compendium
Chris Nickson
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
