What is the differential diagnosis?" I questioned my team, raising my arm with an MRI film in hand, holding it up against the morning light that brightened up the patient's room. A differential diagnosis (or DD, as we like to abbreviate it) is where we list out multiple possibilities by weighing the probability of one disease over another, based on the clinical and radiological features of the patient's symptoms, to work towards an actual final diagnosis. It is a process of clinical reasoning that we exercise to enable appropriate testing, helping us arrive at an answer.

Mrs Gandhi was a 55-year-old lady whose right eye appeared more prominent than the other. She felt pain while moving her right eyeball, and the tiny streaks of red we saw over the white of her eye looked angry and congested. The lower eyelid was swollen and appeared like a prosthetically positioned dark circle. An evening fever had been brewing in the background, but she had brushed it aside. She was capriciously told she had a tumour in the orbit and was sent to us.