The results of the post mortem on Steenkamp were not made public during the Paralympian's bail hearing last week, which resulted in the 26-year-old being released to await trial for pre-meditated murder.
Pistorius appeared at a police station in Pretoria on Monday to comply with the conditions of his bail
But the Daily Mail reports that the victim's family were given the grim news, with family members who saw Steenkamp before her funeral last Tuesday apparently confirming that she had "sustained horrific head injuries".
Reports before the bail hearing suggested that a bloodied cricket bat found at the scene would be the "key piece of evidence" in the trial, with forensic tests set to confirm whose blood is on the bat.
It is thought that the prosecution did not mention the cricket bat at the bail hearing in order not to give away the central argument of their case before the trial, though the defence mentioned a blood-covered cricket bat found in Pistorius's possession during the hearing.
The Pistorius family suffered a further blow on Sunday night as news emerged that Oscar's brother Carl Pistorius is awaiting trial for culpable homicide – South Africa's equivalent of manslaughter – for a car crash in which a woman died in 2008.
Oscar Pistorius also faces further embarrassment in the coming weeks if reports are accurate that he is about to take delivery of a £200,000 McLaren MP4-12C sports car, a present he bought himself in January to celebrate his golden achievements at London 2012.
Photo: Oscar Pistorius at his bail hearing (Reuters)