Retroperitoneal Abscess and Psoas Muscle Abscess

The retroperitoneal space is the area outside the peritoneum at the back of the abdominal cavity. A retroperitoneal abscess is a collection of pus in this retroperitoneal space. It can develop due to spread of an infection from adjacent organs or an infection of the blood as is seen with other types of intra-abdominal abscesses (abscess in the abdomen). Renal and gastrointestinal diseases are the most common conditions leading to a retroperitoneal abscess. A psoas abscess is also a type retroperitoneal abscess. It is collection of pus in the iliopsoas muscle compartment and can drain downwards to present as a swelling in the upper part of the thigh.

Causes of Retroperitoneal Abscess

The spread of an infection from an adjacent organ or neighboring structure is the most important cause of a retroperitoneal abscess. It therefore occurs as a complication of other diseases like :

• Renal disease – kidney stones and/or infections of kidney account for almost 50% of retroperitoneal abscess.
• Gastrointestinal disease – Crohn’s disease, appendicitis, or diverticulitis accounts for 10 to15% of abscess in the retroperitoneal space.
• Bone infections – osteomyelitis, tuberculosis of spine
• Distant sites – infections may spread through the blood from distant locations and is seen in about 10% of retroperitoneal abscesses.
• Other – formation of an abscess following surgery or trauma.

Types of Bacteria in a Retroperitoneal Abscess

Most abscesses are due to a bacterial infection although a minority of cases may be seen with fungal infections. The bacteria responsible for the retroperitoneal abscess are closely related to its cause. The infections of the kidney are usually caused by bacteria like Proteus spp or Escherichia coli.

A retroperitoneal abscess resulting from gastrointestinal disease is usually multibacterial. It may be associated with Escherichia coli, enterococci, Enterobacter and/or Bacteroides. Infections spreading through the blood are usually associated with staphylococci while bone infections are associated with tuberculosis bacteria (Mycobacterium tuberculosis). Escherichia coli (E.coli) is the most common bacteria isolated from retroperitoneal abscesses.

Signs and Symptoms

Retroperitoneal abscesses are usually seen in patients with chronic predisposing diseases like recurrent kidney stones, diabetes mellitus, gastrointestinal diseases, or human immunodeficiency virus (HIV) infection. The signs and symptoms of these diseases may therefor also be present. The common clinical features of retroperitoneal abscesses usually last for more than a week. It includes :

• Abdominal pain or flank pain
• Pain in the groin, hip or referred pain to the knee in a psoas abscess
• Fever with chills
• Weakness and malaise
• Loss of weight