A man who went to hospital because of blood in his urine was diagnosed with a rare condition in which the testicle creates a hard shell around itself.
When they examined the 80-year-old, doctors found his right testicle was unusually large, while the left one was a normal size.
The testicle was also 'stony hard' to touch, the team of Indian medics revealed in a case report.
It turned out the man had a condition called hydrocele, in which fluid builds up in a sheath which surrounds the testicle.
And he had developed a rare complication called calcification which made calcium from his blood build up over years and create a solid casing.
This led to what the doctors dubbed an 'eggshell calcification of scrotum'.
Doctors at King George's Medical University in Lucknow, around 310miles (500km), revealed the bizarre illness in the journal BMJ Case Reports.
They wrote: 'On physical examination, he was found to have grossly enlarged right testis which was stony hard on palpation with normal left testis.'
They diagnosed him with hydrocele, which is a relatively common condition and affects around one in 100 adult men at some point during their lives.
It happens when fluid builds up around the testicle inside a thin fleshy sac which surrounds it within the scrotum, called the tunica vaginalis.
This may happen because of an infection or blockages in the tubes which carry fluid out of the scrotum.
In this man's case, the doctors discovered his illness had been caused by a parasitic worm infection from a mosquito bite.
However, the complication he developed – calcification of the sac surrounding the testicle – is 'very rare', said the doctors, led by Dr Pavan Kumar.
It was caused by calcium being deposited by the extra blood that was pumping through the area because of the swelling.
Calcium naturally accumulates in the body – it may create kidney stones or similar growths in other organs, or stick to the linings of arteries as plaque.
Dr Kumar and colleagues said the amount of calcium which had built up showed the man had had the infection for a long time.
They wrote: 'Eggshell calcification of scrotum is a rare entity, it indicates a state of chronic infection within the hydrocele sac.'
The man had surgery to drain the fluid from his testicle and remove the calcium. The doctors did not reveal how well he recovered.