MADRID, Spain (CNN) -- Cuban leader Fidel Castro personally made the decision to undergo a type of operation that subsequently went wrong instead of a more routine surgery, according to new details published by Spain's El Pais newspaper on its Web site Wednesday.

According to unnamed medical sources that El Pais said are familiar with Castro's case, Castro decided against undergoing an ileostomy -- in which an artificial anus is opened to the abdomen -- when he had problems with diverticulitis in July.

Instead, El Pais said, he underwent a trickier operation to connect part of the colon to the rectum. The newspaper said Castro chose that option because he hoped it would put him back on his feet faster, rather than triggering a prolonged recovery during which he would have to wear a surgical bag.

According to El Pais, complications developed, including the fact that the wound did not heal properly. That led to other problems including peritonitis, or the inflammation of the abdominal cavity, which resulted in at least two further operations.

In its Wednesday report, El Pais said that between summer and December 21, Castro's condition worsened at times and improved at times. The newspaper indicated Castro, 80, remained "prostrate in a serious condition," according to the unnamed medical sources it was quoting.

In Tuesday editions, El Pais -- one of Spain's largest and most reliable newspapers -- indicated Castro's medical team was having to drain more than half a liter of gastric fluids out of Castro's body daily. Wednesday, it said doctors had been carrying out that procedure shortly before the Dec. 21 visit of Dr. Jose Luis Garcia Sabrido, the Madrid-based surgeon who visited Castro after flying to Cuba. El Pais said there has been no further news regarding Castro's condition since Garcia Sabrido's visit.

After Garcia Sabrido completed his visit to Cuba, he gave a Madrid news conference in late December, saying that Castro had undergone a serious operation, but that his situation had stabilized and he was recovering.

El Pais's Wednesday report would seem to indicate it was providing previously undisclosed details about Castro's condition and operations, but it conceded that its information predates Garcia Sabrido's visit.

On Tuesday, El Pais reported Castro's prognosis was "very grave," citing medical sources from the Hospital Gregorio Maranon de Madrid, where Garcia Sabrido is chief of surgery. He said Tuesday he was not the source of the El Pais report.

Castro has not been seen in public since he was first reported to have undergone intestinal surgery on July 31, when he shifted power temporarily to his brother Raul.

Details of his condition have been guarded closely by the Cuban government, which has released at least one video of him since then.

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