New York, Feb 8 (IANS): Ever heard of a tumour under a fingernail? Even the man who has been diagnosed with one didn’t believe it.

The man, in his 40s, noticed a dark line under his nail after an injury, which he assumed was a splinter.

But the mark remained in the same place for three years without changing, according to media reports.

When the patient eventually sought help at a Pennsylvania hospital, doctors observed that he had a two-millimetre-wide black vertical streak in his nail that appeared as though he had a foreign object lodged underneath his nail.

But a biopsy of the object revealed that the man actually had a benign nail tumour known as onychocytic matricoma, according to a report published in the American Medical Association's journal JAMA Dermatology.

“In this case, the tumour affected the tissue beneath the nail, known as the lunula,” said Doris Day, a dermatologist at Lenox Hill Hospital in New York City, who was not involved in the man's case.

The lunula is the whitish, half-moon shaped region at the base of the nail where new nail cells are formed.

Nail tumours do not always have colour, as this man's tumour did, Day informed.

“Tumours of the nail are more common than people realise,” Day said, noting that sometimes, these tumours are mistaken for nail fungus.

Though most of these tumours are benign but malignant tumours such as melanoma can also occur in the nail.

The man had his tumour removed, and there was no recurrence after a year, the reports added.