A trans man who had his penis constructed from skin from his forearm developed stony growths in his urethra.

Doctors said the condition the 22-year-old developed was 'rare' and that they didn't know how to treat it.

The stones, which were blocking the patient from going to the toilet properly, had to be dissolved using a laser.

In a case report the medics said using flesh from the forearm to construct a penis for trans men is the 'gold standard' but very often causes complications.

Doctors in Portugal released photos of the urethra before (left) and after (right) they used a laser to destroy the stones. Pictured middle, during the laser treatment

Doctors from a university hospital in the city of Coimbra, Portugal – about 80miles (128km) south of Porto – revealed the case in a medical journal.

They diagnosed the man, who had transitioned from female to male in 2014, with urethral lithiasis.

Urethral lithiasis is the formation of salt-like stones in the urethra – the tube through which urine is carried along the penis.

These are similar to kidney stones, which are a common condition and are believed to affect more than one in 10 people.

However, the doctors said in the journal BMJ Case Reports that it was rare to see the condition after sex change surgery, so they had to improvise a treatment.

They said the man's urethra had become narrowed and had small hairs on the inside of it which may have encouraged the condition to develop.

Using a laser powered by the element holmium, which is also used to shrink enlarged prostates, the team managed to destroy the crumbled stones.

WHAT IS LITHIASIS/KIDNEY STONES? Urinary lithiasis is a condition known more commonly as kidney stones, which are small hard growths of minerals in the kidneys, bladder and urethra. Kidney stones are common and affect more than one in 10 people, according to the NHS, with 30 to 60-year-olds most likely to develop them. They can cause severe pain and may be urinated out if they're small, or require surgery to remove. The stones are made up of waste products from the blood which build up over time. Things which can increase someone's risk of developing stones include not drinking enough water or taking certain medications such as cold and flu drugs, high blood pressure meds or corticosteroids. Source: NHS and UW Health Advertisement

They released photos of the lithiasis which show it looking like a build up of hundreds of small pieces of gravel stuck to the lining of the urethra.

'Despite the high rates of recurrence in the literature, we have now a follow-up of 40 months without complications,' they wrote in their case report.

'[This] may indicate that laser holmium is an effective tool in the treatment of urologic complications, namely in the treatment of neourethral lithiasis.'

Between 0.6 and one per cent of people in the UK and US are estimated to be transgender, but only a small proportion of these have reassignment surgery.

And surgery to transition from male to female is far more common than vice versa, past research has found.

Having a penis constructed from skin on the forearm is considered the be the most effective way of doing it but the Portuguese doctors said about 80 per cent of patients suffer from complications.

This, they suggested, may be because the blood supply isn't good enough and the urethra may be unusually wide or narrow.

The team's patient needed to use a catheter for two weeks but after the laser treatment remained healthy for a three-year follow-up.