Koirala's personal doctor Kabir Nath Yogi has advised him for a medical check-up in a well-equipped hospital, the Prime Minister's personal aide said.
According to a statement released today, "During a CT scan, a scar has been seen in his lungs."
Yogi said further medical tests are being carried out on the Prime Minister.
Koirala, who is suffering from lung infection for some time, has been taking medicines regularly for bronchitis.
He has been suffering from dry cough and fever since three weeks, the statement said.
Koirala, who has been visiting New York every year for follow up check-ups after he underwent surgery for tongue cancer a few years ago, has been advised for a check-up in the month of June, his aides said.
While visiting the US for a regular medical check-up, the Prime Minister will also undergo detailed examination for other health conditions this time, said Basanta Gautam, chief secretary of the Prime Minister's Office.