The Extraperitoneal Spaces Normal and Pathologic Anatomy

The extraperitoneal portion of the abdomen has always been considered a difficult region in terms of anatomic definitions, clinical evaluation, and radiologic diagnosis. Anatomically, it has been vaguely considered as occupying the posterior half of the abdomen, without well-defined fascial boundaries. Clinically, it is commonly recognized that extraperitoneal effusions are difficult to diagnose. The area is not accessible to the bedside modalities of auscultation, palpation, or percussion. Symptoms and signs may be obscure, delayed, nonspecific, or misleading.

Extraperitoneal tissues do not react as acutely and severely to bacterial contamination as does the peritoneal cavity.1 Known amounts of bacteria introduced intra-peritoneally result in acute peritonitis and dramatic constitutional signs. When introduced into the extraperi-toneal tissues, however, they cause a more smoldering infection. This explains the prolonged duration of the symptoms of extraperitoneal abscess before operation or death, often as long as 2 months.2

Several reports emphasize the difficulties in clinically recognizing even severe extraperitoneal infection. Indeed, in large series, the diagnosis has been completely overlooked in 25-50% of the patients.2,3 Unless diagnosed early and treated adequately, extraperitoneal abscess is associated with prolonged morbidity and high mortality.

Extraperitoneal infection is usually secondary, a complication of infection, injury, or malignancy in adjacent retroperitoneal or intraperitoneal organs. Only rarely is it a consequence of bacteremia or suppurative lymphadenitis.

The predominant symptoms of an extraperitoneal infection are chills, fever, abdominal or flank pain, nausea, vomiting, night sweats, and weight loss. The clinical course is usually insidious, and the initial symptoms are so nonspecific that the correct diagnosis is usually not considered. Constitutional symptoms may be present for weeks to months before localizing signs develop. With pressure on the extraperitoneal nerves, pain may be referred to the groin, hip, thigh, or knee, with little or no complaint of abdominal or back pain. Urologic symptoms are rare, even with perirenal abscess.

A mass or swelling of the flank is palpable about 50% of the time,3 but only if it is large or localizes inferiorly below the costal margin. Almost all patients exhibit tenderness to palpation over the abscess. Scoliosis, psoas spasm, and a sinus tract may be other clinical signs. Although there is invariably leukocytosis, urinalysis may be normal, even in perirenal abscess.

Unusual complications of extraperitoneal abscess include rupture into the free peritoneal cavity and progressive dissection in the soft tissues. Spread may involve the anterior abdominal wall, subcutaneous tissues of the back or flank, subdiaphragmatic spaces, mediastinum, thoracic cavity, psoas muscle, thigh, or hip. A fistula may extend from the kidney into the extraperitoneal portion of the bowel or into a bronchus.

Extraperitoneal blood is usually caused by trauma, ruptured aneurysm, malignancy, bleeding diathesis, or over-anticoagulation.

Extraperitoneal gas is most often the result of bowel perforation secondary to inflammatory or ulcerative disease, blunt or penetrating trauma, a foreign body, iat-rogenic manipulation, or a gas-producing infection originating in extraperitoneal organs. The underlying condition may be chronic, occult, or only suspected clinically. Often it is not until the gas is recognized ra-

diologically that attention is directed to or confirms the presence of an acute process in the abdomen. Extraperitoneal gas is seen as mottled lucencies within the tissues or as linear shadows tracking along fascial planes.

Radiologically, loss of visualization of the lateral margin of the psoas muscle has been considered the hallmark of extraperitoneal effusions. This sign, however, is unreliable since 25-44% of normal individuals show unequal visualization of the psoas borders.4,5

An editorial in Lancet has woefully highlighted the problem:6

Many a clinical reputation lies buried behind the peritoneum. In this hinterland of straggling mesenchyme with ... its shadowy fascial boundaries, the clinician is often left with only his flair and his diagnostic first principles to guide him.

It is essential to realize that this is no longer true. Rather, roentgen-anatomic studies by Meyers et al. have clarified the fascial relationships that clearly demarcate the region into three distinct compartments.7-12 Each has specific boundaries and relationships that can be recognized. Radiologic identification by retroperitoneal pneumography of the renal fascia enclosing the contents of the perirenal space was described by Meyers,13 and the structure was subsequently noted on urography and nephrotomography11,12,14-16 and then definitively on computed tomography.7,17-19 The pathways of flow, preferential routes of spread from various sites, and margin-ation of infection or other effusions within a particular extraperitoneal compartment are guided primarily by the fixed fascial planes and paths of least resistance. This information permits the recognition of the presence, extent, and localization of fluid and gas collections in the extraperitoneal tissues and often pinpoints the precise site of origin and nature of the fluid.

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Responses

  • Bisrat
    What does linear tracking along fascial planes mean?
    5 years ago

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