The centenarian probably passed away in March, an initial examination of the body suggested.
Borgoglio's 65-year-old son, who lived with his mother in the flat near Biella in Piedmont, was taken into police custody and charged with concealing a corpse, according to local paper Eco di Biella.
Neighbours contacted police after becoming concerned about the state of the pensioner's health and her son's evasiveness about her condition, leading officers to make the gruesome discovery.
Police said they found the body in the apartment's kitchen, near a fridge, Il Fatto Quotidiano said. The paper also reported that neighbours had seen the son bring an unusually large new freezer into the building recently.
The family of two had moved to Trivero del Varesotto about a year earlier, during which time the son had struggled to find work.
Local police said they were working to establish the circumstances surrounding Borgoglio's death and were unable to elaborate on the cause.
However, there have been several cases in Italy of children concealing the bodies of their deceased parents while continuing to collect their pensions. In 2014, a 51-year-old was arrested for fraud and hiding a corpse after it was discovered he had concealed the body of his mother for over a year, continuing to draw her pension.
Earlier that year, the body of another woman, Paola Puricelli, was found in the freezer of her home in Borgomanero, in the Piedmont region. She had died four years earlier. Her daughter told police she kept the body so that she could “always be close” to her mother but also admitted that having not worked for years and been refused bank loans, she “survived” off her mother's pension.