When to send a patient for MRI in a case of 3rd nerve palsy and why ?

Third nerve palsy

Paralysis of the third cranial nerve presents to the ophthalmologists because of the common ptosis and/or diplopia.
A common initial response is to send the patient to do an MRI which turns out NORMAL in 90% of cases.

In a “poor” country with limited resources, economics of health is a top issue and i will write a post on waste in health care, as my assumption is that it mounts to 50% of expenditure.

So in clear words when to send a patient for MRI in a case of 3rd nerve palsy and why is this perplexing?
The dilemma is because of textbooks using terms like “most pupil sparing palsies are vascular but not all” while the problem is much easier.

You have to differentiate between COMPLETE nerve palsy and INCOMPLETE palsy
If you have a complete palsy of all muscles supplied and complete ptosis but a NORMAL pupil DO NOT DO an MRI, this is a vascular accident of the nerve.

IF the pupil is DILATED do an MRI whatever the degree of involvement of other muscles
One situation remains; partial ptosis and free pupil, you have 2 options:
-treat one week, if becomes complete and pupil free—-no MRI
-if you are light hearted do an MRI.

Good morning and may GOD bless Egypt