Colorectal Surgery

Approximately 2 weeks ago, my grandmother had to undergo a resectioning of her decscending colon.  According to the surgeon, this procedure was performed in order to remove a benign

Benign ear cyst or tumor
Benign positional vertigo

tumor.  Prior to her surgery, my grandmother was an extremely active 70 year old woman

Women's way

and was in a fairly healthy condition for her age with the exception of two musculoskeletal surgeries and the placement of two cardiac

Cardiac catheterization
Cardiac tamponade
Left heart ventricular angiography

stents

Abdomen - swollen
Brain herniation
Chronic persistent hepatitis
Coronary artery stent
Hyperemesis gravidarum
Lyme disease - chronic persistent
Stent

.   She was admitted and a battery of diagnostic tests were performed.  Several diagnosese were give, from apendicitis to colitis

Colitis
Irritable bowel syndrome
Ischemic colitis
Necrotizing enterocolitis
Salmonella enterocolitis
Ulcerative colitis

all over the course of 3-4 weeks with the appropriate courses of treatment for each, but without success.  Finally, a colonoscopy was performed and it was determined that she did in fact have an obstructed colon and that a resectioning was needed.  After the resectioning, my grandmother did not recover as expected and she continued to have severe pain and infection.  An emergency colonoscopy was order and the gastroenterologist's findings was that there appeared to by some inflammation around the resected area of the colon along with an area that appeared to be necrotic.  With that, the surgeon reopened that origninal surgical site and removed an additional section of her colon and placed an external colostomy.  The surgeon also reported that her abdominal cavity was full of infection and that there was leakage from the colon.

My question is, "what could have caused this necrosis of her colon after resectioning" and "shouldn't the surgeon have reassured that there was an adequit  blood supply to the colon and that the colon was adequitly sutured by testing it prior to closing"?