Diverticulitis: This condition is characterized by inflammation of the diverticula in the colon wall, which can lead to leakage of contrast into the pericolonic space or within the colon itself. Given the location in the left hemicolon and rectum, diverticulitis is a common and plausible explanation.

Colonic Perforation: A perforation in the colon can allow contrast to leak into the surrounding tissues or into the colon lumen itself, especially if the perforation communicates with the lumen. This could be due to various causes such as diverticulitis, cancer, or trauma.
Rectal or Colonic Fistula: An abnormal connection between the colon or rectum and another organ or the skin could allow contrast to enter the colon or rectum from an external source or vice versa.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause inflammation and ulceration of the colon and rectum, potentially leading to leakage of contrast.

Colon Cancer with Perforation: Although less common, a perforated colon cancer can lead to contrast leakage and is critical to diagnose early due to its significant impact on treatment and prognosis.
Ischemic Colitis: Reduced blood flow to the colon can cause necrosis and perforation, leading to contrast leakage. This condition requires prompt diagnosis and treatment to prevent severe outcomes.
Traumatic Injury to the Colon: In cases of abdominal trauma, the colon can be injured, leading to perforation and contrast leakage. This diagnosis is critical in the context of trauma.

Intussusception: Although more common in children, intussusception (the telescoping of one segment of intestine into another) can occur in adults and could potentially cause contrast to be seen in unusual locations within the colon.
Colonic Volvulus: A twisting of a portion of the colon can impede blood flow and cause ischemia, potentially leading to perforation and contrast leakage. This condition is less common but requires urgent attention.