A Dangerous Evolution of Retroperitoneal Infection to Infrarenal Abdominal Aortic Pseudoaneurysm: A Case Report
This case report illustrates the critical importance of serial imaging and early surgical intervention in a patient with recurrent diverticulitis who developed a rare, life-threatening mycotic pseudoaneurysm of the infrarenal abdominal aorta following an initial presentation of nonspecific retroperitoneal inflammation.
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In the deep space behind the abdominal organs lies a region called the retroperitoneum, a quiet corridor where the body's largest artery, the aorta, runs down toward the legs. Normally, this area is shielded from the chaotic infections that can occur in the intestines. However, when bacteria breach their usual boundaries, they can invade the wall of the aorta, turning a sturdy vessel into a fragile, infected balloon. This condition, known as a mycotic pseudoaneurysm, is a rare and terrifying complication. The term "mycotic" is a historical name that suggests a fungal cause, but in reality, these infections are usually driven by bacteria. The danger lies in the speed of the damage; the infection eats away at the artery's structural integrity, causing it to bulge and potentially burst, leading to massive internal bleeding. Because the early signs are often vague—just a dull ache or general sickness—doctors frequently miss the warning until it is too late.
This story begins with a forty-six-year-old man who had spent the last two years fighting a recurring battle with a severe intestinal condition called diverticulitis. This illness had already caused him to develop five separate pockets of infection in his pelvis, which required drainage and antibiotics. Despite these setbacks, he had recently undergone surgery to remove the diseased section of his colon, and for a brief moment, it seemed the crisis had passed. Then, three days of back pain, nausea, and vomiting brought him back to the emergency room. His blood work told a story of a body under siege, with white blood cell counts soaring and markers of severe infection rising high. When doctors scanned his abdomen, they found a large, five-centimeter mass of inflamed tissue wrapped tightly around the lower part of his aorta. At first glance, it looked like a lingering abscess, a pocket of pus that had not fully cleared.
The medical team moved quickly to understand what they were seeing. They performed a biopsy, a procedure where a small sample of the tissue is taken to check for cancer or active infection. The results were confusing. The tissue sample showed no signs of active bacteria or cancer, and the mass appeared to be resolving on its own. Based on this, the patient was sent home with instructions to return for follow-up. However, the body was hiding a more dangerous truth. Just one month later, a routine scan revealed that the situation had changed dramatically. The area that had looked like a resolving mass had transformed into a new, two-centimeter bulge on the aorta itself. This was not just inflammation; the artery wall had been weakened by the infection and was now ballooning outward, forming a pseudoaneurysm. The infection had silently eaten through the vessel wall, creating a ticking time bomb.
The patient returned to the hospital with worsening symptoms, including fevers, night sweats, and severe pain. The medical team realized that the initial biopsy had likely missed the active infection because the bacteria were deep within the vessel wall or had been temporarily suppressed by earlier antibiotics. They began a broad course of powerful antibiotics to fight the unseen invaders. Because the patient had poor dental health, which can sometimes be a source of bacteria entering the bloodstream, doctors also removed a problematic tooth to eliminate any potential source of reinfection. Despite these measures, the infection proved stubborn. While in the hospital, the patient developed a new fluid collection near his groin that grew a type of yeast, and later, a different type of bacteria was found in his blood, linked to a medical tube in his arm. This complex mix of infections required a tailored, multi-drug approach to clear.
The definitive solution required surgery. The team knew that simply patching the infected artery would likely fail because the surrounding tissue was too contaminated. Instead, they performed a major open operation. They removed the infected section of the aorta entirely and tied off the vessel. To keep blood flowing to the legs, they created a new path for the blood to travel, bypassing the abdomen completely by routing a graft from the arm down to the legs. They also cleaned out the infected area inside the abdomen and covered the surgical site with a flap of the patient's own omentum, a fatty tissue that helps fight infection and heal wounds. The patient spent time in the hospital recovering from this extensive procedure, eventually completing six weeks of intravenous antibiotics followed by a month of oral medication.
The outcome of this case offers a critical lesson for medical practice. The patient's journey showed how an infection can evolve from a seemingly manageable mass into a life-threatening vascular emergency in a matter of weeks. The initial scan had shown inflammation, but the true danger—the formation of the aneurysm—was not visible until it had already developed. This rapid progression suggests that in patients with a history of severe abdominal infections, a single scan is not enough. Doctors must remain vigilant, using repeated imaging to watch for subtle changes that signal the artery is being compromised. While the patient's tissue cultures came back negative for bacteria, the clinical picture and the eventual growth of other organisms confirmed that an infection was indeed driving the process. By combining aggressive surgery with long-term antibiotic therapy, the team successfully prevented a rupture and saved the patient's life. This case highlights that even when tests appear normal, the body can be undergoing a silent, dangerous transformation that requires constant monitoring and decisive action.
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