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Subject: Retroperitoneal Abscess
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A collection of purulent fluid located in the space between the peritoneum and transversalis fascia lining the posterior abdominal cavity
Classified as primary if spread hematogenously or secondary if spread through infection of an adjacent organ
The retroperitoneum can be further subdivided into three compartments:
Anterior pararenal space
Second and third segments of the duodenum, pancreas, bile duct, portal and splenic veins, appendix, ascending/descending colon, transverse mesocolon
Kidneys, renal vessels, adrenal glands
Posterior pararenal space
Contains no major organs and is filled with fat, blood vessels, and lymphatics
Bounded by renal fascia and the muscles of the posterior abdominal wall
Most common in the 3rd to 6th decades (1)
Slight male predominance (1)
Bowel perforation secondary to neoplastic disease, diverticulitis, pancreatitis, pancreatic cancer, retroperitoneal appendicitis, biliary tract disease, peptic ulcer disease, inflammatory bowel disease, peritonitis, colonoscopy following GI surgery, bowel infarction (1)
Genitourinary (GU) extravasation secondary to obstruction, nephrolithiasis, pyelonephritis, urinary tract infection, urologic surgery, pelvic surgery, ovarian cancer
Osteomyelitis of vertebral bodies or 12th rib, epidural abscess (1)
Less common causes are trauma, hematogenous or lymphatic seeding from a distant infection, or postoperative complication (1).
Infection seeds a confined space within the retroperitoneum.
Can be a monomorphic or polymorphic predominance of organisms
Typically consists of normal flora from adjacent organs (i.e., GI, GU, and female reproductive tract)
Hypoxia and lack of appropriate blood supply limit effective immune response.
Osmotic forces produce growth of abscess cavity.
Mycobacterium tuberculosis was previously a common pathogen but is less common today.
Most common pathogens
Consider necrotizing enterocolitis as an etiology in newborns (3).
Chronic urinary retention
GU tract obstruction
Inflammatory bowel disease
Malignancy of the GU, GI, or female reproductive tract
Osteomyelitis of the spine or ribs
Pelvic inflammatory disease
Recent surgery of GU or GI
Treatment of the primary disease
Prevention of infection, such as perioperative antibiotic prophylaxis
Prompt treatment of symptomatic infection
Immunosuppression (HIV, glucocorticoid use)
Malignancy (GI or GU)
Surgery (GI or GU)
Urinary tract infections
Insidious onset of nonspecific symptoms of infection including fever, chills, weight loss, nausea/vomiting, flank pain, low back pain, abdominal pain or groin pain, lethargy, and altered bowel habits (4)
Most common form of presentation is triad of fever, lumbar pain, and lumbar mass.
History of GU, GI, female reproductive tract surgery or instrumentation, recent GI or GU infection, malignancy, osteomyelitis of a vertebral body, epidural abscess, inflammatory bowel disease, TB
Associated conditions: diabetes, renal insufficiency, immunosuppression
Chronically ill-appearing patient with intermittent spiking fever, tachycardia
Tenderness to palpation of the lower abdomen, flank, groin, proximal thigh, costolumbar sensitivity ± rigidity and fullness or can be nonspecific, nonlocalized abdominal pain
Mass is potentially palpable in the abdomen, flank, thigh, groin, or scrotum.
Pleuritic pain may occur due to diaphragmatic irritation.
If there is pressure on adjacent nerves, referred pain may be felt in the groin, thighs, or knees (4).
Check for psoas sign: pain elicited by hyperextension or flexion of the hip (5)
Laboratory findings are often nonspecific and variable.
CBC usually reveals leukocytosis with a shift to the left and possibly anemia (1).
ESR is elevated.
BUN and creatinine may present azotemia.
Gram stain and blood culture
Urinalysis may reveal pyuria, proteinuria, and hematuria.
Aerobic, anaerobic, and fungal cultures
CT scan of the abdomen and pelvis is the diagnostic modality of choice (2).
Gas within a low-density mass is pathognomonic for an abscess.
Ultrasound (US) can show fluid collections but not as precise as CT (6).
Abscesses appear as echoic masses with irregular walls. Can have poorly defined shadows and high refractive content is indicative of gas.
MRI show abscesses are more visible on T1-weighted images (2).
Kidney, ureter, bladder (KUB) may reveal an absent psoas shadow, scoliosis, loss of renal outline, or soft tissue mass (1).
Chest x-ray (CXR) may reveal an elevation of the ipsilateral diaphragm, pleural effusion, basilar atelectasis, or lower lobe infiltrate.
Radionuclide imaging has high radiation exposure, low diagnostic specificity, and technical difficulty and may reveal false positive with pyelonephritis, acute tubular necrosis, and neoplasms (1,6).
Percutaneous drainage via CT, MRI, or US of the abscess cavity
Contraindications: presence of coagulation disorders and calcified masses (can indicate benign cyst, renal artery aneurysm, renal neoplasm, hydatid cyst) (6)
Specimens should be sent for aerobic, anaerobic, and fungal cultures.
Require close observation for signs of sepsis.
Serial CT scanning to confirm drainage
For suspected GI source, single-agent therapy (ertapenem, ticarcillin/clavulanate) or combination therapy (quinolone or cephalosporin + metronidazole) can be used empirically (7)[B].
Routine use of aminoglycosides is not recommended unless evidence of resistant organisms due to potential toxicity (7)[B].
Ampicillin/sulbactam is not recommended secondary to high resistance rates in community-acquired E. coli (7).
Empiric coverage for methicillin-resistant Staphylococcus aureus (MRSA) is only recommended for health care–associated infections and in those known to be colonized (7)[B].
Empiric coverage for yeast is not recommended (7)[B].
Quinolone-resistant E. coli are common in some areas (7)[B].
For suspected GU source (i.e., renal or perinephric abscesses), the organism in the urine culture typically parallels the bacteriology of the abscess.
If cultures are positive, narrow antibiotic coverage based on the results.
Duration of treatment is based on clinical improvement.
Diagnostic delay and postponed treatment increase mortality rate.
In patients requiring surgical drainage and are high-surgical risk, CT-guided percutaneous drainage as a temporary measure is suitable.
Percutaneous drainage should not be delayed especially in high-risk surgical patients.
Surgical drainage is performed when
Percutaneous drainage is not possible
Failure of percutaneous drainage attempt
Multiple or multiloculated abscesses
Purulent material is too thick to drain.
Persistence of fever after 48 to 72 hours of appropriate antibiotic coverage
If the primary cause must be addressed surgically, such as urinary tract stone, perforated bowel, malignancy
Some secondary causes—that is, intestinal fistula, necrotic tumors, and osteomyelitis—tend to do better with surgery than percutaneous drainage.
Reimage depending on clinical progress.
Close monitoring of drains and irrigated appropriately
Remove drain when
Drainage is <10 mL/day or becomes serous.
Resolution of abscess on imaging
Patient is clinically improved with absence of fever and improvement of leukocyte count.
Treatment with antibiotics alone is associated with a 100% mortality rate (1).
Treatment with surgical drainage alone is associated with a 31% mortality rate (1).
Treatment with surgical drainage plus broad-spectrum antibiotic coverage is associated with a 16% mortality rate (1).
Mortality rate is higher with
Higher temperature (>104°F)
Presence of underlying disease process, such as diabetic ketoacidosis
White blood cell (WBC) count >25,000 cells/μL
Positive blood cultures
Marked reduction in mortality with early diagnosis, immediate drainage, and antibiotic coverage
Abscess may cross the midline into another space.
Deep vein thrombosis (DVT)
Fistula formation to stomach, small bowel, duodenum, lung
Perforation through diaphragm
Rupture into peritoneum
K68.19 Other retroperitoneal abscess
K68.11 Postprocedural retroperitoneal abscess
K68.12 Psoas muscle abscess
N15.1 Renal and perinephric abscess
567.38 Other retroperitoneal abscess
998.59 Other postoperative infection
567.31 Psoas muscle abscess
590.2 Renal and perinephric abscess
32362007 Retroperitoneal abscess (disorder)
2471009 Postoperative intra-abdominal abscess (disorder)
266463007 Iliopsoas abscess (disorder)
80640009 Perirenal abscess (disorder)
Rare condition in which perirenal abscesses are more common.
CT scan of the abdomen and pelvis is the diagnostic modality of choice.
Insidious onset of nonspecific symptoms
Close observation for signs of sepsis