"The MRI blew us away," Jesse's mother, Michelle, said yesterday.
"We were absolutely devastated. It was the worst day of our lives."
Jesse had a risky operation at Starship children's hospital in September to take a biopsy for testing, but the laboratory result on the tissue sample was inconclusive.
It showed inflammation, which the lab report indicated could be from an infection or from a cancerous tumour.
"They said it hasn't come back as tumour tissue and they are still classing it as some type of infection, which is the best news out of the two," Mrs Bessant said yesterday.
Jesse's father, Shane, said the surgeon asked them after the biopsy if Jesse had been overseas.
"It's a medical mystery."
Paediatric neurologist Dr Rakesh Patel said the questions about overseas travel were because of the possibility - an unlikely one, however - that the inflammation in Jesse's brain stem was caused by a parasite.
"Is there a bug out there that might cause this? There's nothing in the books to suggest this is a bug of some sort.
"Putting [the lab report] with the MRI and the clinical presentation, infection is very unlikely. It is very likely to be a tumour."
Now Jesse faces having another MRI, and possibly another five-hour biopsy operation in the hope of obtaining definitive lab results.
Jesse's parents, wary of putting him through another risky biopsy operation, believe there is little hope of saving their "miracle baby" - he was conceived by IVF - if he has a cancerous tumour, because its location makes it inoperable and any treatment would be only to prolong his life.
Dr Patel said "You could consider chemotherapy. Where it is, it's going to be hard to operate. It's technically difficult, the question is would he be left with disability."
But Jesse's parents want to explore the infection angle thoroughly and are fund-raising for the possibility of taking him overseas for tests and treatment.
"He's such a happy kid," said Mrs Bessant. "The thought of him being taken away is just so unfair."
