LIVER ABSCESS
Liver abscesses account for up to half of visceral intraabdominal abscesses and are caused most commonly by biliary tract disease (due to aerobic gram-negative bacilli, enterococci) and less often by local spread from other contiguous sites of infection (mixed aerobic and anaerobic infection) or hematogenous seeding (infection with a single species, usually staphylococci or streptococci). Pts have fever, anorexia, weight loss, nausea, and vomiting, but only ~50% have signs localized to the RUQ, such as pain, tenderness, hepatomegaly, and jaundice. Serum levels of alkaline phosphatase are elevated in ~70% of pts, and leukocytosis is common. About one-third of pts are bacteremic. Amebic liver abscesses are not uncommon; amebic serology has yielded positive results in >95% of affected pts. Drainage remains the mainstay of treatment, but medical management with long courses of antibiotics can be successful. Percutaneous drainage tends to fail when there are multiple, sizable abscesses; viscous abscess contents that plug the pigtail catheter; associated disease (e.g., of the biliary tract); or lack of response in 4-7 days.

SPLENIC ABSCESS
Splenic abscesses usually develop by hematogenous spread of infection (e.g., due to endocarditis). Abdominal pain or splenomegaly occurs in ~50% of cases and pain localized to the left upper quadrant in ~25%. Fever and leukocytosis are common. Chest x-ray may show infiltrates or left-sided pleural effusions. Splenic abscesses are most often caused by streptococci; S. aureus is the next most common cause. Gram-negative bacilli can cause splenic abscess in pts with urinary tract foci, and Salmonella can be responsible in pts with sickle cell disease. The diagnosis is often made only after the pt's death; the condition is frequently fatal if left untreated. Pts with multiple or complex multilocular abscesses should undergo splenectomy, receive adjunctive antibiotics, and be vaccinated against encapsulated organisms (Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis). Percutaneous drainage has been successful for single, small (<3-cm) abscesses and may also be useful for pts at high surgical risk.

PERINEPHRIC AND RENAL ABSCESSES
More than 75% of these abscesses are due to ascending infection and are preceded by pyelonephritis. Areas of abscess within the renal parenchyma may rupture into the perinephric space. The most important risk factor is the presence of renal calculi that produce local obstruction to urinary flow. Other risk factors include structural abnormalities of the urinary tract, a history of urologic surgery, trauma, or diabetes. E. coli, Proteus spp. (associated with struvite stones), and Klebsiella spp. are the most common etiologic agents. Clinical signs are nonspecific and include flank pain, abdominal pain, and fever. The diagnosis should be considered if pts with pyelonephritis have persistent fever after 4 or 5 days of treatment, if a urine culture yields a polymicrobial flora in pts with known renal stone disease, or if fever and pyuria occur in conjunction with a sterile urine culture. Treatment includes drainage and the administration of antibiotics active against the organisms recovered. Percutaneous drainage is usually successful.

PSOAS ABSCESS
Psoas abscesses arise from hematogenous seeding or from contiguous spread from an intraabdominal or pelvic source or from nearby bony structures (e.g., vertebral bodies). S. aureus is most common when the source is hematogenous or bony; a mixed enteric flora is likely with an abdominal source. Pts have fever, lower abdominal or back pain, or pain referred to the hip or knee.

For a more detailed discussion, see Baron MJ, Kasper DL: Intraabdominal Infections and Abscesses, Chap. 121, p. 807, in HPIM-17.