Figure 8-11 Axial computed tomographic image at the level of the kidneys demonstrates air in the anterior pararenal space bilaterally in patient with perforated sigmoid diverticulitis. On the right side, air also enters the perirenal space and retrorenal plane (between the layers of the posterior renal fascia).

Figure 8-58 Utility of bone windows for identifying ureteral calculi adjacent to ureteral stent. A, Axial image from noncontrast-enhanced computed tomographic scan viewed in soft-tissue windows demonstrates a single high-attenuation object within the ureter, presumed to be the stent. B, When the same axial image is viewed with bone windows, a ureteral stone can be identified adjacent to the stent.

CHAPTER 8 Imaging Evaluation of Acute Abdominal Pain

Neal C. Dalrymple, Michael Oliphant, John R. Leyendecker

ACUTE ABDOMINAL PAIN: A DIAGNOSTIC DILEMMA

Acute abdominal pain is a common clinical syndrome and a diagnostic dilemma for clinicians. For centuries, physicians relied on obtaining a history of illness that elicited characteristic clinical symptoms. This history, combined with careful elicitation of physical examination findings, allowed physicians to discriminate among many potential disease processes. Unfortunately, historical, physical examination, and laboratory data are often nonspecific and inconclusive, spurring a shift in the diagnostic approach to patients with abdominal pain toward imaging. As with physical examination, image interpretation is facilitated by familiarity with the relevant anatomic structures and common diagnoses to be considered in patients presenting with specific pain syndromes (Table 8-1).

Table 8-1 Causes of Acute Abdominal Pain Based on Location of Symptoms

Location of Pain	Relevant Structures and Common Diagnoses to Consider
Right upper quadrant	Cardiopulmonary: pneumonia, pulmonary embolism, acute myocardial infarction Gallbladder: cholelithiasis, acute cholecystitis, torsion Liver: abscess, tumor, hepatitis, hemorrhage, hepatic necrosis Bile ducts: obstruction, choledocholithiasis, cholangitis, bile leak, hemobilia from biopsy or other trauma Hepatic flexure: diverticulitis, colitis, tumor, obstruction, epiploic appendagitis Duodenum: peptic ulcer, perforation, duodenitis, obstruction Omentum: segmental omental infarction Peritoneum: perihepatitis (Fitz–Hugh–Curtis syndrome)
Left upper quadrant	Cardiopulmonary: pneumonia, pulmonary embolism, acute myocardial infarction Stomach: peptic ulcer, gastritis, tumor, obstruction Spleen: infarction, hemorrhage, tumor Pancreas: acute pancreatitis, pancreatic cancer Splenic flexure: diverticulitis, colitis, tumor, obstruction, ischemia Peritoneum: abscess
Midepigastric	Esophagus: esophagitis, reflux disease, dysmotility, tumor, impaction Stomach: peptic ulcer, gastritis, tumor, obstruction, volvulus Duodenum: peptic ulcer, perforation, duodenitis, obstruction Pancreas: pancreatitis, pancreatic cancer Abdominal wall: ventral hernia Aorta: aneurysm (with or without rupture)
Right lower quadrant	Appendix: appendicitis Ileum: Crohn disease, infectious enteritis, Meckel diverticulitis Colon: colitis, diverticulitis, epiploic appendagitis, perforated tumor, perforated foreign body, ischemia Adnexa: cyst, endometriosis, torsion, tuboovarian abscess, ectopic pregnancy Abdominal wall: hernia
Left lower quadrant	Colon: diverticulitis, perforated tumor, perforated foreign body, colitis, ischemia Adnexa: cyst, endometriosis, torsion, tuboovarian abscess, ectopic pregnancy Abdominal wall: hernia
Generalized	Bowel: obstruction (neoplastic, inflammatory, or volvulus), ileus, ischemia, perforation, inflammation Peritoneum: peritonitis, pneumoperitoneum Aorta: aneurysm (with or without rupture)
Flank and back	Kidney and ureters: ureterolithiasis, pyelonephritis/abscess, embolism/infarction, venous thrombosis, cyst rupture, hemorrhage, nephritis Adrenal gland: hemorrhage Appendix: appendicitis (retrocecal) Aorta: aneurysm (with or without rupture), dissection Musculoskeletal: trauma, infection, hemorrhage, neoplasm, disc herniation, spinal stenosis
Pelvis and groin	Adnexa: cyst, endometriosis, torsion, tuboovarian abscess, ectopic pregnancy Uterus: endometritis, obstruction, rupture Rectosigmoid colon: colitis/proctitis, ischemia, diverticulitis, foreign body Small bowel: inflammation Appendix: appendicitis Bladder and ureters: bladder outlet obstruction, ureteral calculus, cystitis Lymph nodes: lymphadenitis Abdominal wall: hernia Peritoneum: abscess
Scrotal or inguinal	Testis: torsion, orchitis, abscess, hematoma Epididymis: epididymitis Bowel and peritoneum: hernia

Keep in mind that significant overlap exists between the diseases listed in Table 8-1 and their clinical presentations. A confusing influence in the diagnosis of abdominal pain is related to the overlapping innervation of the abdominal organs. For example, there exists considerable overlapping innervation of the stomach (T5-7), biliary tract (T6-8), and pancreas (T5-9). Therefore, a gastric process can be difficult to differentiate from biliary colic or pancreatitis based on location of pain alone. Overlapping innervation of structures such as the colon (T10-L1), small bowel (T8-10), and kidney (T10-L1) can obscure the precise origin of pain elsewhere in the abdomen as well. Also, remember that abdominal organs do not always reside in their expected locations. For example, the cecum and appendix have a notorious propensity to extend to locations beyond the right lower quadrant, and patients with situs anomalies or bowel malrotation are not uncommon. Finally, disease processes often present remote from their organ of origin. Inflammation and tumor can spread via the subperitoneal space within the ligaments and mesenteries of the abdomen and pelvis or via the peritoneal space. Knowledge of these pathways of disease spread as discussed in Chapter 6 can greatly facilitate image interpretation and explain apparent discrepancies between the clinical presentation and the actual diagnosis.

Pitfall: Overlapping innervation, developmental anatomic variations, and potential mobility of the abdominal organs combined with complex pathways of disease spread can result in apparent discrepancies between a patient’s clinical presentation and the actual diagnosis. The astute radiologist understands these complexities and applies imaging to provide a cohesive explanation for the patient’s symptoms.

The role of laboratory data in narrowing a differential diagnosis should not be underestimated. At a minimum, a radiologist interpreting an imaging study of a patient with acute abdominal pain should be familiar with the patient’s blood cell counts, liver function tests, amylase and lipase levels, and urinalysis if they are available.

Not all imaging modalities are equally capable of demonstrating the structures and disease processes listed in Table 8-1. For example, computed tomography (CT) would be an inappropriate first test to perform in a patient presenting with scrotal pain, whereas transabdominal ultrasound would be a poor choice for excluding peptic ulcer disease. Therefore, when imaging is deemed necessary for further evaluation of a patient’s pain, the first decision to make involves the choice of imaging modality. A carefully optimized protocol must be selected and combined with appropriate patient preparation to maximize the effectiveness of the chosen modality.

COMPUTED TOMOGRAPHY: THE WORKHORSE OF THE EMERGENCY DEPARTMENT

Why Computed Tomography Rules the Emergency Department

Despite the wide variety of available imaging options, CT has been adopted as the modality of choice for the evaluation of patients presenting with acute abdominal pain not clearly localized to the right upper quadrant or pelvis (in females of child-bearing age). The use of plain radiographs in the acute setting has come under criticism, mainly because of low sensitivity of conventional radiography for most common causes of abdominal pain. Some studies recommend use of unenhanced CT of the abdomen and pelvis rather than abdominal radiography, arguing that plain films rarely provide a specific diagnosis. CT is much more likely than plain radiographs to show a specific cause of abdominal pain and can be useful in distinguishing between those processes that require urgent surgical intervention and those suitable for conservative management. Several studies have shown that routine evaluation of the abdomen and pelvis with CT in the emergency setting decreases both the number of hospital admissions and the length of stay in the emergency department.

Although ultrasound is routinely performed for the evaluation of right upper quadrant and pelvic pain, CT has many advantages over sonography for the evaluation of patients with other types of pain. CT can be performed in a matter of seconds on a modern scanner, allowing surgical triage to be accomplished with utmost efficiency. CT is less limited by patient body habitus, and displays all organ systems and many disease processes with near equal clarity. Finally, CT image quality is far less operator dependent than sonography.

One final advantage of CT is its exquisite ability to demonstrate the full extent of a disease process that spans multiple abdominal organ systems or abdominal compartments. No other modality has the ability of CT to fully document the spread of diseases via the peritoneal cavity or abdominal mesenteries and ligaments. This avoids the potential diagnostic pitfall created by diseases presenting remote from their organs of origin.

Computed Tomography Protocol Considerations for Acute Abdominal Pain

Because of the overlapping innervation of abdominal and pelvic organs and the possibility of a disease process presenting remote from the organ of origin, the entire abdomen and pelvis should be included on a CT examination performed for evaluation of acute abdominal pain. Although CT performed without the addition of enteric and intravenous contrast media can provide valuable diagnostic information, the appropriate use of these agents often improves sensitivity and defines disease to better advantage. For this reason, most survey examinations of the abdomen and pelvis for acute pain are performed using both intravenous and enteric (typically oral) contrast. The portal venous phase of enhancement is preferred in most situations. The CT examination can be modified to accommodate specific patient conditions, such as renal insufficiency, contrast sensitivity, or compromised hemodynamic status.

Traditional positive oral contrast (high attenuation) is useful for distinguishing bowel from other structures and for demonstrating perforation of the gastrointestinal tract. Negative oral contrast (low attenuation) accompanied by injection of intravenous contrast media can be useful for demonstrating inflammation and other enhancing lesions of the bowel wall (Fig. 8-1). When urgency dictates, examinations can be performed without enteric contrast media.

Figure 8-1 Coronal reformation of computed tomography performed with intravenous and negative oral contrast demonstrates varices within the fourth part of the duodenum. The scan was performed to evaluate abdominal pain and occult gastrointestinal bleeding in a patient with prior placement of a portosystemic shunt that was found to be thrombosed on this examination.

Helpful Computed Tomographic Findings in the Acute Abdomen

Because of the all-inclusive survey provided by CT and the overlapping clinical presentations that can cloud the origins of abdominal pain, radiologists must be facile with interpreting CT scans of the abdomen and pelvis. This skill requires a systematic approach and knowledge of findings that aid in disease localization. A number of signs have been proved effective in localizing the source of acute abdominal pain (Box 8-1).

Focal Fat Stranding or Fascial Thickening

Fat stranding adjacent to a bowel loop or solid organ is often a key CT finding indicating the origin of pain. Stranding is seen as linear or hazy increased attenuation within a region of fat, usually caused by fluid or inflammatory cells infiltrating the tissues (Fig. 8-2) and often accompanied by thickening of nearby fascial planes. Stranding is most useful when it is localized because generalized stranding is nonspecific and can be seen with any systemic cause of edema (e.g., congestive heart failure or hypoproteinemia). Focal fat stranding can signal a focus of acute disease and should always prompt focused inspection of the adjacent structures.

Figure 8-2 Axial image from a contrast-enhanced computed tomographic scan of the upper abdomen demonstrates fat stranding anterior to the pancreas in a patient with acute pancreatitis.

Disproportionate fat stranding refers to focal stranding adjacent to bowel associated with minimal or absent bowel wall thickening. Its presence suggests entities that typically result in a greater degree of inflammation in the adjacent mesentery than in the bowel wall itself. The presence or absence of disproportionate fat stranding is one method used to differentiate colonic diverticulitis from colon cancer, because diverticulitis tends to result in a greater degree of pericolic inflammation relative to the degree of bowel wall thickening (Fig. 8-3). Disease processes associated with disproportionate fat stranding are listed in Table 8-2.

Figure 8-3 Axial computed tomographic images from two patients demonstrate how the presence of disproportionate fat stranding can help to differentiate between (A) diverticulitis and (B) colon cancer.

Table 8-2 Disease Processes Associated with Disproportionate Fat Stranding

Diagnosis	Clinical Discriminators	Imaging Discriminators
Appendicitis	Right lower quadrant pain, nausea, fever, leukocytosis	Periappendiceal inflammation
Diverticulitis	Left lower quadrant pain, fever, leukocytosis	Pericolonic inflammation, adjacent diverticulum
Epiploic appendagitis	Nausea and fever are rare	Fatty pericolonic mass with dense rim and central high-attenuation focus
Omental infarction	Right-sided greater than left-sided pain Nausea and fever are rare	Triangular or ovoid fatty/heterogeneous lesion deep to right anterior abdominal wall

Mesenteric fat stranding can result from a broad variety of inflammatory and neoplastic disease processes; therefore, it is important to consider this finding in the context of clinical presentation and other imaging findings (Fig. 8-4). The most common causes of mesenteric fat stranding are listed in Box 8-2.

Figure 8-4 Axial images from contrast-enhanced computed tomography of the (A) abdomen and (B) pelvis demonstrate fat stranding because of omental torsion. Stranding extended into the right inguinal canal where the omentum was tethered by a hernia.

Sclerosing mesenteritis is an uncommon primary inflammatory disorder of the mesentery. An elusive disease that can be difficult to diagnose and to treat, sclerosing mesenteritis has been known by many names, including mesenteric panniculitis, retractile mesenteritis, fibrosing mesenteritis, mesenteric lipodystrophy, and mesenteric Weber–Christian disease. The most common CT finding is fat stranding in the mesentery, a nonspecific finding sometimes referred to as a “misty” mesentery (Fig. 8-5). Additional findings of sclerosing mesenteritis may include: (1) a “fat halo,” or ring of low attenuation surrounding mesenteric vessels within a region of mesenteric fat stranding; (2) a dense pseudocapsule surrounding the area of involved fat; and (3) small soft-tissue nodules within the affected region of mesentery.

Figure 8-5 Axial image from contrast-enhanced computed tomography (CT) in a patient with upper abdominal pain demonstrates a well-defined region of hazy fat stranding within the mesentery. In the absence of other evidence of disease, a diagnosis of sclerosing mesenteritis was made, and the findings were followed by CT.

(Courtesy Srinivasa R. Prasad, M.D.)

The most common malignant neoplasms to involve the mesenteries are lymphoma and carcinoid tumor, although other tumors, such as adenocarcinoma, can also extend into the mesenteries or incite a local desmoplastic reaction. Neoplastic disease of the mesentery rarely presents as acute abdominal pain.

Perinephric stranding is commonly seen in healthy individuals, but when asymmetric, should prompt a search for a cause. Some causes to consider include obstructive urinary calculus, pyelonephritis, inflammatory nephritides, renal infarction, and renal vein thrombosis.

Segmental Bowel Dilatation

Bowel becomes distended when the intestinal tract is obstructed or when there is a decrease in normal bowel motility. In the case of obstruction, the proximal gastrointestinal tract distends, unless partially decompressed by vomiting or nasogastric tube suction. In cases of decompressed obstruction, bowel distention may be limited to the immediately proximal segment.

Adynamic or paralytic ileus is often associated with a generalized decrease in bowel motility, resulting in relatively uniform distention of the small intestine and colon. However, a focal area of inflammation in the peritoneal cavity can result in segmentally decreased motility in bowel loops immediately adjacent to the acute process. This accounts for the “sentinel loop” sign associated with intraabdominal inflammation (Fig. 8-6) and can be a clue to the nature and location of the underlying disease process.

Figure 8-6 Axial image from contrast-enhanced computed tomographic scan performed in a patient with pancreatitis demonstrates focal dilatation of a jejunal loop adjacent to mesenteric stranding. This is comparable with the sentinel loop sign described on plain radiographs.

Segmental Bowel Wall Thickening

Distinguishing between normal and abnormal bowel wall thickness is one of the greatest challenges in abdominal imaging. Even the combination of a diligent technologist and compliant patient rarely results in uniform bowel distention throughout the gastrointestinal tract. Because some bowel loops are likely to be incompletely distended during the examination, it is common to mistakenly describe a collapsed bowel segment as “thickened.” Of course, if one becomes accustomed to ignoring apparently thickened loops of bowel, critical diagnoses can be missed.

If a bowel loop appears thickened, it is useful to look for a segment of that loop that contains air. Because air rises to the most nondependent portion of the lumen and produces some degree of luminal distension, the presence of air underlying apparent bowel wall thickening suggests that the loop in question is truly abnormal.

Be cautious about calling wall thickening in the jejunum on CT examinations. The normal jejunum contains many more redundant folds than ileum. The CT correlate of redundant folds in the jejunum is a thicker appearance of the bowel wall (Fig. 8-7). As stated earlier, looking for areas of nondependent air between folds may help distinguish normal from thickened jejunum.

Figure 8-7 Axial image from contrast-enhanced computed tomographic examination performed in an asymptomatic patient to follow a small liver lesion demonstrates the differences in appearance between normal jejunum and ileum. Note the redundant folds of the normal jejunum results in a thickened appearance when compared with the ileum.

Whereas thickening of the entire cecum can be seen with colitis or colon cancer, focal thickening of the cecal apex near the base of the appendix is often seen with acute appendicitis. Sometimes called the cecal arrow sign, wall thickening at the junction of the cecum and appendix causes the lumen of the cecum to point toward the appendix, supporting the diagnosis of acute appendicitis (Fig. 8-8).

Figure 8-8 Cecal arrow sign in acute appendicitis. Axial computed tomographic image demonstrates focal thickening of the cecum at its junction with an inflamed appendix. The high-attenuation enteric contrast within the cecum tapers to “point” toward the appendix.

Table 8-3 lists the disease processes most commonly associated with segmental thickening of the bowel wall on CT, as well as some parameters that can be used to refine the differential diagnosis.

Table 8-3 Diseases Associated with Segmental Bowel Wall Thickening

Diagnosis	Imaging Discriminators
Appendicitis	Thickening of appendix and adjacent cecal apex Appendicolith Interruption in enhancing appendiceal wall Periappendiceal fat stranding or fluid
Crohn disease	Thickened segment of distal ileum Skip lesions Fistulas and interloop abscesses
Colonic diverticulitis	Fat stranding usually more severe than wall thickening Eccentric wall thickening Adjacent diverticulosis
Gastritis	Thickening of gastric wall Usually more severe in the antrum
Malignancy	Bowel wall thickening more severe than fat stranding Eccentric wall thickening Loss of wall stratification on enhanced images Pericolonic lymphadenopathy
Meckel’s diverticulitis	Blind ending loop from ileum, not from cecum

Extraluminal Gas

PNEUMOPERITONEUM

The interpretation of CT examinations performed for acute abdominal pain should always include a directed search for peritoneal gas. Gas usually rises to the most nondependent recesses of the peritoneal cavity; therefore, a focused survey along the anterior peritoneal surface can increase sensitivity. During the search, it is helpful to use window and level settings that allow differentiation between fat and gas. The peritoneal space extends into the fissures for the ligamentum teres and ligamentum venosum, so include those locations in the search pattern. When gas is present in these fissures, duodenal or distal stomach perforation is often the source (Fig. 8-9). The most common causes of pneumoperitoneum are listed in Table 8-4.

Figure 8-9 Axial image from contrast-enhanced computed tomographic scan demonstrates pneumoperitoneum in the fissure for the ligamentum venosum (FVL) and anterior to the liver. A perforated duodenal ulcer was found at surgery. Note that the window/level settings are set to make air darker than fat.

Table 8-4 Causes of Pneumoperitoneum

Surgical Causes (90%)^*	Nonsurgical Causes (10%)
Bowel perforation Penetrating injury	Recent laparotomy Transabdominal peritoneal or enteric catheter Mechanical ventilation Pulmonary disease Spontaneous bacterial peritonitis Pneumatosis cystoides intestinalis Scleroderma Retrograde passage through female genital system

* Requirement for urgent, often surgical, therapy.

Notably, many causes of pneumoperitoneum do not require emergent therapy. The most common among these is postoperative pneumoperitoneum. Gas in the peritoneal cavity can be a normal finding up to 10 days after surgery. This can be confounding in a postoperative patient with acute abdominal pain or signs of infection. Postoperative peritoneal gas is typically seen in trace amounts after the first few days and should decrease in quantity on successive examinations. An increase in gas over time raises concern for complications.

Pitfall: Although pneumoperitoneum can persist for up to 10 days after abdominal surgery, increasing gas can be a sign of infection, breakdown of a bowel anastomosis, or perforated postoperative stress ulcer. If a patient is imaged repeatedly for suspected complications, pay close attention to the quantity and distribution of gas.

Iatrogenic pneumoperitoneum can also occur when air is inadvertently injected into a peritoneal dialysis catheter. As with postoperative pneumoperitoneum, the presence of a dialysis catheter does not prove that gas in the peritoneal space is an insignificant finding in the patient with acute abdominal pain. Pneumoperitoneum is also occasionally seen when a percutaneous gastrostomy tube is present. Retrograde passage of air through the female genital tract has been reported in association with sexual activity and pelvic examination, as well as with activities such as horseback riding and water skiing.

PNEUMORETROPERITONEUM

Extraperitoneal gas is usually the result of bowel perforation or infection. Because gas is more restricted within the extraperitoneal compartments than within the peritoneal cavity, the location of gas within the retroperitoneum is often more useful for identifying the source. In general, by determining whether the gas is within the anterior pararenal space, the perirenal space, or posterior pararenal space, and noting whether it is unilateral or bilateral, the differential diagnosis can be narrowed considerably. The most likely causes for retroperitoneal gas within each space are outlined in Table 8-5.

Table 8-5 Correlation between Location of Extraperitoneal Gas and Its Source

Compartment	Side	Likely Source
Anterior pararenal	Right	Perforation of descending duodenum (e.g., duodenal ulcer or recent ERCP) (Fig. 8-10)
	Left	Perforation of descending or sigmoid colon (e.g., diverticulitis)
	Bilateral	Sigmoid or rectal perforation (Fig. 8-11) Complicated pancreatitis
Perirenal	Right or left	Renal infection
Posterior pararenal	Left	Perforated sigmoid diverticulitis
Posterior pararenal	Bilateral	Rectal perforation (traumatic) Supradiaphragmatic origin (pneumomediastinum)

Figure 8-10 Axial image from noncontrast-enhanced computed tomographic examination performed after difficult endoscopic retrograde cholangiopancreatogram demonstrates air in the right anterior pararenal space. The patient recovered with conservative management.

INTRAMURAL GAS COLLECTIONS

Pneumatosis intestinalis describes gas in the wall of the alimentary tract. Because the gas is confined between the mucosal and serosal layers, pneumatosis does not move freely through the abdomen and is usually confined to one region of the intestinal tract. On plain film, pneumatosis appears as a combination of curvilinear and mottled gas, and can easily be confused with fecal material (Fig. 8-12). Although the curvilinear shape of the gas collections are better appreciated by CT, differentiation from fecal material can still be challenging. Because the mucosal and serosal layers can be thin when distended, pneumatosis can be difficult to detect when located adjacent to gas within the bowel lumen. However, when fluid is present adjacent to intramural gas, the gas is much more conspicuous.

Figure 8-12 Pneumatosis of the colon demonstrated by (A) abnormal radiograph and by (B) computed tomographic scan in a patient with an obstructing cancer of the hepatic flexure.

Most of the many causes of intestinal pneumatosis are listed in Table 8-6. Pneumatosis is often seen in association with acute gastrointestinal disease processes such as bowel ischemia, bowel obstruction, and severe bowel infections. When seen in the presence of bowel ischemia, it is associated with reported mortality rates of 50% to 75%. However, pneumatosis is also associated with chronic disease processes such as obstructive pulmonary disease, Whipple disease, and scleroderma. Iatrogenic pneumatosis can result from endoscopy with or without biopsy, barium enema, or bowel surgery, particularly if a bowel anastomosis is performed. Occasionally, idiopathic pneumatosis is seen as an unsuspected finding in patients without acute abdominal symptoms. When pneumatosis is present, always look at the mesenteric vessels and liver for evidence of portal venous gas (Fig. 8-13).

Table 8-6 Causes of Intestinal Pneumatosis

Causes that Usually	Causes that Usually
Require Urgent Therapy	Do Not Require Therapy
Bowel ischemia Severe bowel infections Bowel obstruction Trauma	Mechanical ventilation Chronic obstructive pulmonary disease Recent endoscopy Barium enema Recent bowel surgery Whipple disease Scleroderma Systemic lupus erythematosus Idiopathic

Figure 8-13 Axial images from computed tomographic examination performed for development of abdominal distention after resuscitation from recent cardiac arrest demonstrate (A) extensive portal venous gas in association with (B) colonic pneumatosis.

As with the bowel, gas can also collect within the walls of other structures such as the gallbladder (emphysematous cholecystitis) and the urinary bladder (emphysematous cystitis). These entities are almost always infectious in nature and particularly common in individuals with diabetes. Gas within the vagina (vaginitis emphysematosa) is an uncommon but clinically benign entity characterized by gas-filled mucosal cysts. Although vaginitis emphysematosa can be associated with organisms such as Trichomonas vaginalis, it does not represent a life-threatening gas-producing infection.

OTHER GAS COLLECTIONS

A contained collection of extraluminal gas near bowel is a common sign of perforation with or without abscess formation. Abscesses contain infected material with variable proportions of fluid, debris, and gas (Fig. 8-14). Common causes of abscess include bowel perforation, superinfected postoperative fluid, hematogenous dissemination of bacteria, pyelonephritis, or anastomotic leak. Because the bowel also contains differing proportions of gas, fluid, and semisolid material, it is sometimes mistaken for an abscess. A key feature that distinguishes an abscess from bowel is discontinuity or eccentric location with respect to the alimentary tract. When an abscess is identified near a bowel loop without evidence of diverticula or inflammatory bowel disease, be certain to look for a foreign body such as a fish bone.