BRADY TWP — A woman suffered serious head injuries when she was thrown from or fell off a horse Saturday afternoon, authorities said.

The woman, believed to be in her early-50s, reportedly underwent surgery at a Pittsburgh hospital for a fractured skull and bleeding on the brain. Her condition was not known.

Emergency officials said the woman was by herself riding the horse on the 700 block of Muddy Creek Drive in Brady Township shortly before 1 p.m. when the accident happened.

Her head possibly struck a wooden fence after she was thrown or fell, said Mike Pflugh, assistant chief for the Unionville Volunteer Fire Department.

Authorities also did not rule out the possibility that the horse could have stepped on the woman’s head after she fell.

A resident found the unconscious woman underneath the fence. The back of her head was badly injured.

A Butler Ambulance Service crew treated her before she was taken to the Unionville fire station on Mahood Road, where a medical helicopter landed before flying her to Allegheny General Hospital in Pittsburgh.

She remained unresponsive throughout, Pflugh said.