Medical School · Year 3 · General Surgery · includes a quiz and discussion video

Seminar 04: Acute Abdomen

Year 3: General Surgery Clerkship

Learning Objectives

By the end of this seminar, students will be able to:

1. Develop a systematic approach to abdominal pain evaluation
2. Differentiate surgical from non-surgical causes of acute abdomen
3. Identify clinical features requiring emergent intervention
4. Apply appropriate imaging strategies
5. Recognize specific conditions presenting as acute abdomen
6. Describe initial management and resuscitation

Seminar Outline

I. Approach to Acute Abdomen

The acute abdomen represents a clinical syndrome characterized by abdominal pain of less than one week duration that requires urgent evaluation to determine the need for surgical intervention versus medical management. This presentation encompasses a wide spectrum of conditions ranging from benign, self-limited processes to life-threatening emergencies requiring immediate operative intervention. The fundamental challenge facing the clinician is to rapidly differentiate patients requiring emergent surgery from those who can be managed conservatively or with delayed intervention. Time is a critical factor in many conditions presenting as acute abdomen, as delays in diagnosis and treatment of conditions such as perforated viscus, strangulated bowel, and mesenteric ischemia directly correlate with increased morbidity and mortality.

The surgical abdomen specifically refers to conditions requiring operative intervention, and the primary goal of the initial evaluation is to identify these patients while simultaneously resuscitating and preparing them for surgery. Not all acute abdominal pain is surgical, and many conditions including gastroenteritis, urinary tract infections, and musculoskeletal pain can mimic surgical emergencies. Conversely, some serious surgical conditions may present with subtle findings that can be easily overlooked, particularly in elderly, immunocompromised, or obtunded patients. The systematic approach combining thorough history, careful physical examination, appropriate laboratory testing, and judicious use of imaging allows for accurate triage in the majority of cases.

Understanding the pathophysiology of abdominal pain guides the diagnostic approach and helps explain the clinical presentations of various conditions. Visceral pain arises from stimulation of afferent nerve fibers in the walls of hollow organs or capsules of solid organs, typically caused by distension, ischemia, or inflammation, and is characteristically dull, poorly localized, and often described as cramping or colicky. Parietal pain results from irritation of the parietal peritoneum, which receives somatic innervation, producing sharp, well-localized pain that is exacerbated by movement or coughing and is often accompanied by guarding and rebound tenderness. Referred pain occurs when visceral afferent fibers converge with somatic afferents at the spinal cord level, producing pain perceived at a distant site, such as shoulder pain from diaphragmatic irritation or back pain from retroperitoneal processes.

The location of abdominal pain provides important diagnostic information based on the anatomic structures present in each region. Right upper quadrant pain suggests hepatobiliary pathology including cholecystitis, choledocholithiasis, and cholangitis, as well as hepatitis, hepatic abscess, and right lower lobe pneumonia with referred pain. Left upper quadrant pain is less common but may indicate splenic pathology, pancreatitis, or gastric processes. Right lower quadrant pain classically suggests appendicitis but must be differentiated from cecal pathology, ovarian conditions, ectopic pregnancy, and mesenteric adenitis. Left lower quadrant pain most commonly indicates diverticulitis in older patients but may also represent sigmoid colon pathology, ovarian conditions, or constipation. Epigastric pain suggests peptic ulcer disease, pancreatitis, gastritis, or referred pain from cardiac ischemia. Diffuse abdominal pain raises concern for generalized peritonitis from perforation, mesenteric ischemia, or late presentation of localized processes.

<image>Panel A: An anatomical diagram of the abdomen divided into nine regions with lists of differential diagnoses for each region including right upper quadrant showing cholecystitis, hepatitis, and pneumonia, right lower quadrant showing appendicitis, ovarian pathology, and cecal diverticulitis, left lower quadrant showing sigmoid diverticulitis and ovarian pathology, and epigastric region showing peptic ulcer disease and pancreatitis. Panel B: A cross-sectional illustration demonstrating the three types of abdominal pain with visceral pain arising from hollow organ distension, parietal pain from peritoneal inflammation, and referred pain pathways from the diaphragm to the shoulder. Panel C: A clinical photograph showing a patient with board-like abdominal rigidity indicating diffuse peritonitis requiring emergent surgical intervention. Panel D: A flowchart showing the initial approach to acute abdomen starting with vital signs and resuscitation, proceeding through history and examination, laboratory studies, imaging decision, and surgical consultation criteria.</image>

II. History and Physical Examination

The history of present illness in acute abdominal pain requires systematic characterization of the pain using standard frameworks while remaining alert to the diagnostic implications of each feature. The onset of pain provides crucial information, with sudden, severe pain suggesting perforation of a hollow viscus, rupture of an aneurysm, or torsion, while gradual onset is more typical of inflammatory conditions such as appendicitis or cholecystitis. The duration and progression pattern help distinguish between processes that are worsening, stable, or improving. The location of pain at onset and any subsequent migration provides important diagnostic information, as the classic migration of appendicitis pain from periumbilical to right lower quadrant reflects the progression from visceral to parietal irritation as inflammation extends to the peritoneum.

The character and quality of pain help identify the underlying pathophysiology. Colicky pain that waxes and wanes suggests obstruction of a hollow viscus such as bowel, ureter, or biliary tree, with peristaltic waves causing intermittent distension and pain. Constant, unrelenting pain suggests ischemia, perforation, or established peritonitis. Burning pain may indicate peptic ulcer disease or gastritis. The radiation of pain follows characteristic patterns, with biliary pain often radiating to the right scapula, pancreatic pain radiating straight through to the back, ureteral colic radiating to the groin, and diaphragmatic irritation causing referred shoulder pain. Factors that aggravate or alleviate pain provide additional diagnostic information, with peritonitis worsened by movement and relieved by lying still, while obstruction pain may be partially relieved by vomiting.

Associated symptoms help narrow the differential diagnosis and assess disease severity. Nausea and vomiting are common but nonspecific, with the timing relative to pain onset providing some diagnostic value, as vomiting that precedes pain suggests gastroenteritis while vomiting following the onset of pain is more typical of surgical conditions. The character of vomitus is important, with bilious vomiting suggesting obstruction distal to the ampulla of Vater and feculent vomiting indicating distal small bowel or colonic obstruction. Fever suggests an infectious or inflammatory process. Changes in bowel habits including diarrhea, constipation, or obstipation help localize pathology to the gastrointestinal tract. Urinary symptoms may indicate urologic causes of abdominal pain. In women of reproductive age, menstrual history, vaginal discharge, and possibility of pregnancy are essential elements of the history.

The past medical and surgical history, medications, and social history provide context for the current presentation and may suggest specific diagnoses. Previous abdominal surgeries increase the risk of adhesive small bowel obstruction and alter anatomy that may affect interpretation of findings. Medications including NSAIDs, anticoagulants, and immunosuppressants have important implications for certain diagnoses and treatment. Cardiovascular disease and atrial fibrillation increase the risk of mesenteric ischemia. Alcohol use raises concern for pancreatitis and variceal bleeding. Family history of inflammatory bowel disease, familial adenomatous polyposis, or hereditary cancer syndromes may be relevant. The functional status and comorbidities help assess surgical risk and influence treatment decisions.

<image>Panel A: A mnemonic diagram for abdominal pain history showing OPQRST elements including Onset, Palliating and provoking factors, Quality, Region and radiation, Severity, and Timing, with examples of significant findings for each element. Panel B: An illustration showing the classic migration of appendicitis pain from periumbilical region initially representing visceral pain to right lower quadrant as inflammation involves the parietal peritoneum. Panel C: A differential diagnosis chart correlating associated symptoms with likely diagnoses, showing fever with infectious causes, bilious vomiting with obstruction, bloody stool with ischemia or inflammatory bowel disease, and urinary symptoms with urologic causes. Panel D: A timeline graphic showing how the sequence of pain and vomiting differs between gastroenteritis where vomiting typically precedes pain and surgical conditions where pain typically precedes vomiting.</image>

III. Physical Examination Findings

The abdominal examination begins with inspection before touching the patient, observing for distension, visible peristalsis, surgical scars, skin changes, and the patient's overall appearance and position of comfort. Abdominal distension suggests bowel obstruction, ascites, or massive organomegaly. Visible peristalsis may be seen in thin patients with intestinal obstruction. Surgical scars indicate previous operations that may cause adhesive disease or alter anatomy. Ecchymosis around the umbilicus (Cullen's sign) or flanks (Grey Turner's sign) suggests retroperitoneal hemorrhage, classically from severe pancreatitis. The patient who lies motionless avoiding any movement typically has peritonitis, while the patient writhing in discomfort unable to find a comfortable position is more likely experiencing colicky pain from obstruction.

Auscultation should precede palpation to avoid altering bowel sounds through stimulation. Normal bowel sounds occur every five to fifteen seconds and reflect peristaltic activity. High-pitched, hyperactive bowel sounds in rushes coinciding with cramping pain suggest mechanical bowel obstruction as the bowel contracts against the obstruction. Absent bowel sounds or hypoactive sounds may indicate ileus from peritonitis, late or complete obstruction, or recent surgery. A succussion splash heard when shaking the patient's abdomen suggests gastric outlet obstruction with retained gastric contents. Auscultation may also reveal bruits suggesting vascular pathology including mesenteric ischemia or abdominal aortic aneurysm.

Percussion provides information about the presence of free air, ascites, distended bowel, and organomegaly, and elicits peritoneal signs when pain is produced by the vibration. Tympany over a distended abdomen suggests air-filled dilated bowel, while dullness may indicate fluid, stool, or a mass. Loss of liver dullness, with tympany extending over the normally dull liver area, suggests pneumoperitoneum from perforated viscus. Shifting dullness indicates the presence of ascites. Percussion tenderness, where the vibration caused by percussion produces pain, is a sensitive indicator of peritoneal inflammation and may be positive when direct rebound tenderness is equivocal.

Palpation systematically assesses for tenderness, guarding, rebound tenderness, and masses, beginning gently and away from the area of maximal pain. Voluntary guarding represents the patient's conscious tensing of abdominal muscles in anticipation of pain and may be reduced by having the patient flex the knees and take slow deep breaths. Involuntary guarding, where the abdomen remains rigid despite relaxation techniques, indicates peritoneal irritation and represents an important finding suggesting surgical pathology. Rebound tenderness, pain that occurs when pressure is suddenly released from the abdomen, indicates peritoneal inflammation but is less reliable than other signs and causes significant patient discomfort. Mass palpation may reveal appendiceal phlegmon, diverticular abscess, incarcerated hernia, or malignancy.

<image>Panel A: An illustration of the systematic abdominal examination sequence showing inspection of distension and scars, auscultation for bowel sounds and bruits, percussion for tympany and shifting dullness, and palpation for tenderness, guarding, and masses in the proper order. Panel B: A comparison diagram of voluntary versus involuntary guarding showing voluntary guarding as conscious muscle tensing that relaxes with distraction and knee flexion versus involuntary guarding as persistent rigidity indicating peritonitis. Panel C: A photograph of Cullen's sign showing periumbilical ecchymosis and Grey Turner's sign showing flank ecchymosis indicating retroperitoneal hemorrhage as seen in severe pancreatitis. Panel D: An auscultation findings interpretation guide showing high-pitched rushes indicating mechanical obstruction, absent sounds indicating ileus or late obstruction, and bruits suggesting vascular pathology.</image>

IV. Special Examination Signs

McBurney's point tenderness represents maximal tenderness at a location one-third of the distance from the anterior superior iliac spine to the umbilicus and is the classic finding in acute appendicitis. This location corresponds to the base of the appendix where it attaches to the cecum, and while the exact position may vary with appendiceal anatomy, tenderness in the right lower quadrant remains the most consistent finding in appendicitis. The sensitivity of McBurney's point tenderness for appendicitis is approximately eighty to ninety percent, though it may be absent in early appendicitis when inflammation is limited or in retrocecal appendicitis where the appendix lies posterior and may not irritate the anterior peritoneum.

Rovsing's sign refers to pain felt in the right lower quadrant when palpatory pressure is applied to the left lower quadrant, indicating peritoneal irritation in the right lower quadrant that is sensitive to any transmitted pressure or movement. This sign supports the diagnosis of appendicitis but is less sensitive than direct right lower quadrant tenderness. The psoas sign is elicited by extending the hip against resistance or by having the patient lie on the left side and passively extending the right hip, with pain suggesting inflammation adjacent to the psoas muscle as occurs with retrocecal appendicitis or psoas abscess. The obturator sign is tested by flexing the right hip and knee and internally rotating the hip, with pain suggesting inflammation near the obturator internus muscle as may occur with pelvic appendicitis or pelvic abscess.

Murphy's sign is the classic finding in acute cholecystitis and is elicited by palpating in the right upper quadrant during inspiration. As the patient takes a deep breath, the liver and gallbladder descend, and if the gallbladder is inflamed, contact with the examiner's hand causes sudden pain and inspiratory arrest. A positive Murphy's sign has reasonable sensitivity and specificity for cholecystitis and when positive on ultrasound examination (sonographic Murphy's sign) is even more predictive. The absence of Murphy's sign does not exclude cholecystitis, particularly in elderly or diabetic patients who may have blunted inflammatory responses.

Carnett's sign helps differentiate abdominal wall pain from intraabdominal pathology by having the patient tense the abdominal muscles through partial sit-up while the examiner palpates the area of tenderness. If the tenderness is from the abdominal wall, it will persist or worsen with muscle tensing (positive Carnett's sign) because the tender structure remains under the examiner's fingers, whereas intraabdominal tenderness typically decreases as the tensed muscles protect the underlying viscera. Rectal examination should be performed in patients with acute abdominal pain to assess for mass, tenderness, blood, or prostatic abnormalities, though its yield in appendicitis diagnosis is limited. Pelvic examination in women of reproductive age is essential to evaluate for gynecologic causes of abdominal pain including ectopic pregnancy, ovarian torsion, pelvic inflammatory disease, and tubo-ovarian abscess.

<image>Panel A: An anatomical illustration showing McBurney's point located one-third of the distance from the anterior superior iliac spine to the umbilicus, with demonstration of palpation technique and expected finding of maximal tenderness. Panel B: A demonstration of Rovsing's sign showing left lower quadrant palpation producing referred pain in the right lower quadrant due to peritoneal irritation from appendiceal inflammation. Panel C: Illustration of psoas sign testing with the patient lying on the left side and examiner passively extending the right hip, with pain indicating retrocecal appendicitis or psoas abscess. Panel D: Demonstration of Murphy's sign showing right upper quadrant palpation during inspiration with inspiratory arrest as the inflamed gallbladder contacts the examiner's hand.</image>

V. Laboratory Studies

The complete blood count provides information about the presence and severity of infection or inflammation, though normal values do not exclude serious pathology. Leukocytosis with white blood cell count above ten thousand per microliter with left shift indicating increased immature neutrophils supports the presence of infection or inflammation in conditions such as appendicitis, cholecystitis, and diverticulitis. However, up to twenty percent of patients with proven appendicitis may have normal white blood cell counts, particularly early in the disease course. Severe leukocytosis above twenty thousand raises concern for perforation, abscess, or severe sepsis. Anemia may indicate chronic blood loss from malignancy or acute hemorrhage from ruptured aneurysm, ectopic pregnancy, or gastrointestinal bleeding.

The comprehensive metabolic panel provides information about electrolyte abnormalities, renal function, and hepatic parameters that help assess the patient's condition and guide resuscitation. Electrolyte abnormalities including hypokalemia and metabolic alkalosis are common with vomiting and nasogastric suction, while metabolic acidosis may indicate severe volume depletion, sepsis, or tissue ischemia. Elevated blood urea nitrogen and creatinine may reflect dehydration with prerenal azotemia or underlying renal disease that affects treatment planning. Liver function tests including bilirubin, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase help evaluate hepatobiliary pathology, with elevated bilirubin and alkaline phosphatase suggesting biliary obstruction and elevated transaminases suggesting hepatocellular injury.

Serum lipase is the preferred test for acute pancreatitis, with elevation to at least three times the upper limit of normal having high sensitivity and specificity for the diagnosis. Lipase remains elevated longer than amylase and is less affected by renal function. Serum lactate serves as a marker of tissue hypoperfusion and anaerobic metabolism, with elevation above two millimoles per liter raising concern for sepsis, shock, or mesenteric ischemia. In the context of abdominal pain with risk factors, elevated lactate should prompt consideration of mesenteric ischemia, though lactate elevation is a late finding and a normal value does not exclude early ischemia. Trending lactate levels helps assess response to resuscitation.

Urinalysis helps identify urinary tract infection or nephrolithiasis as causes of abdominal pain and may reveal pyuria or bacteriuria suggesting infection or hematuria suggesting stone disease. Sterile pyuria may occur when an inflamed appendix or other pelvic structure irritates the ureter. A urine or serum pregnancy test is mandatory in all women of reproductive age presenting with abdominal pain, as ectopic pregnancy is a life-threatening condition that can mimic many other causes of acute abdomen. Type and screen should be obtained when hemorrhage is possible or surgery anticipated. Coagulation studies are important in patients on anticoagulation or with liver disease.

<image>Panel A: A laboratory studies interpretation guide for acute abdomen showing expected findings in common conditions with leukocytosis in appendicitis and cholecystitis, elevated lipase in pancreatitis, elevated bilirubin and alkaline phosphatase in biliary obstruction, and elevated lactate in mesenteric ischemia. Panel B: A comparison of normal versus abnormal leukocyte differential showing left shift with bandemia indicating acute bacterial infection. Panel C: A diagnostic algorithm for elevated liver function tests distinguishing obstructive pattern with elevated bilirubin and alkaline phosphatase from hepatocellular pattern with elevated transaminases and their differential diagnoses. Panel D: A flowchart showing mandatory pregnancy testing protocol for women of reproductive age with abdominal pain and the implications of positive versus negative results for subsequent evaluation.</image>

VI. Imaging Modalities

Plain radiography of the abdomen and chest provides rapid, low-cost initial assessment that can identify pneumoperitoneum, bowel obstruction, and foreign bodies, though its sensitivity for many conditions is limited compared to cross-sectional imaging. Upright chest radiograph is the most sensitive plain film view for detecting pneumoperitoneum, with free air visible under the diaphragm in seventy to eighty percent of perforations. If the patient cannot sit or stand, left lateral decubitus abdominal film may demonstrate free air between the liver and lateral abdominal wall. The supine abdominal radiograph can show dilated loops of bowel with air-fluid levels on horizontal beam views, multiple air-fluid levels at different heights within the same loop suggesting bowel obstruction, and the "3-6-9 rule" indicates abnormal dilation when small bowel exceeds three centimeters, colon exceeds six centimeters, or cecum exceeds nine centimeters.

Ultrasound serves as the first-line imaging modality for suspected biliary disease and in pregnant patients or pediatric patients where avoiding radiation is preferred. Right upper quadrant ultrasound has sensitivity above ninety-five percent for detecting gallstones and can demonstrate findings of acute cholecystitis including gallbladder wall thickening greater than three millimeters, pericholecystic fluid, and sonographic Murphy's sign. Ultrasound can evaluate for common bile duct dilation suggesting choledocholithiasis, though the stone itself may not be visualized. For appendicitis, ultrasound with graded compression can visualize a dilated, noncompressible appendix greater than six millimeters with high specificity when positive, though sensitivity is lower than CT particularly in obese patients or when the appendix is retrocecal. Pelvic ultrasound evaluates for ovarian pathology including torsion, hemorrhagic cyst, and ectopic pregnancy.

Computed tomography with intravenous contrast has become the dominant imaging modality for evaluation of acute abdominal pain due to its high sensitivity and specificity for most conditions and ability to provide comprehensive evaluation of the entire abdomen and pelvis. CT findings in appendicitis include an appendix greater than six millimeters in diameter that is non-filling with contrast, periappendiceal fat stranding, and possible appendicolith. Cholecystitis findings include wall thickening, pericholecystic fluid, and gallstones or sludge. Diverticulitis demonstrates colonic wall thickening with pericolonic fat stranding and possible abscess or extraluminal air. Bowel obstruction shows dilated proximal bowel with decompressed distal bowel and identification of a transition point and often the cause. Small bowel wall thickening, mesenteric fat stranding, and vascular occlusion suggest mesenteric ischemia.

CT angiography is the preferred study when mesenteric ischemia is suspected, providing evaluation of the mesenteric vessels and bowel simultaneously. MRI offers advantages in pregnant patients where radiation should be avoided and may be used for appendicitis evaluation with sensitivity and specificity approaching CT. However, MRI availability, longer examination times, and higher cost limit its routine use. The choice of imaging modality depends on the clinical scenario, with consideration of the likely diagnosis, radiation exposure, availability, and patient factors including pregnancy, contrast allergy, and renal function.

<image>Panel A: An upright chest radiograph demonstrating pneumoperitoneum with free air visible as a dark crescent under the right hemidiaphragm, indicating perforated viscus requiring urgent surgical evaluation. Panel B: A CT scan image of acute appendicitis showing dilated appendix greater than six millimeters with periappendiceal fat stranding and an appendicolith visible. Panel C: Right upper quadrant ultrasound image demonstrating acute cholecystitis with gallbladder wall thickening greater than three millimeters, pericholecystic fluid, and multiple gallstones with posterior acoustic shadowing. Panel D: CT scan showing small bowel obstruction with dilated proximal small bowel containing air-fluid levels, decompressed distal bowel, and a transition point at an adhesive band.</image>

VII. Appendicitis

Acute appendicitis represents the most common surgical emergency, with a lifetime risk of approximately seven percent and peak incidence in the second and third decades of life, though it can occur at any age. The pathophysiology typically involves obstruction of the appendiceal lumen by fecalith, lymphoid hyperplasia, foreign body, or rarely tumor, leading to increased intraluminal pressure, impaired venous outflow, bacterial overgrowth, and ultimately ischemia and perforation if untreated. The classic presentation begins with vague periumbilical pain representing visceral afferent stimulation from appendiceal distension, followed over six to twelve hours by migration to the right lower quadrant as inflammation extends to involve the parietal peritoneum. Anorexia is nearly universal and may precede the onset of pain.

Atypical presentations occur commonly and must be recognized to avoid delayed diagnosis. Retrocecal appendicitis, occurring in up to thirty percent of patients, may present with back or flank pain rather than classic anterior abdominal tenderness, and the psoas sign may be more prominent than McBurney's point tenderness. Pelvic appendicitis may cause suprapubic pain, urinary frequency from bladder irritation, and diarrhea from rectal irritation. Pregnant patients present a diagnostic challenge as the enlarging uterus displaces the appendix superiorly and laterally, and normal pregnancy changes including leukocytosis and abdominal discomfort may mask appendicitis. Elderly and immunocompromised patients often have blunted inflammatory responses with minimal fever, leukocytosis, or tenderness, yet higher rates of perforation due to delayed presentation.

Diagnostic evaluation has evolved with the widespread availability of CT imaging, which has sensitivity and specificity exceeding ninety-five percent for appendicitis. However, clinical scoring systems such as the Alvarado score can help stratify patients, with high scores proceeding directly to surgery and intermediate scores undergoing imaging. CT findings include appendiceal diameter greater than six millimeters, wall thickening, periappendiceal fat stranding, and appendicolith when present. Ultrasound is preferred in children and pregnant women, with a non-compressible appendix greater than six millimeters being diagnostic when visualized. MRI without contrast provides excellent accuracy in pregnancy without radiation exposure.

Treatment of uncomplicated appendicitis is appendectomy, performed laparoscopically in most cases with low complication rates and rapid recovery. The timing of surgery for uncomplicated appendicitis is within twelve to twenty-four hours, with no evidence that delay within this window increases perforation risk. Complicated appendicitis with perforation and abscess formation may be managed initially with antibiotics and percutaneous drainage if technically feasible, with interval appendectomy performed six to eight weeks later after inflammation has resolved. This approach reduces the morbidity associated with operating in an acutely inflamed field. Generalized peritonitis from perforation requires emergent surgery. Non-operative management with antibiotics alone has been studied for uncomplicated appendicitis, with success rates of seventy to ninety percent but significant recurrence rates, and remains an option in select patients.

<image>Panel A: A flowchart showing the classic progression of appendicitis from luminal obstruction to mucosal secretion and distension, bacterial overgrowth, impaired venous outflow, ischemia and infarction, and finally perforation, with corresponding clinical symptoms at each stage. Panel B: An anatomical illustration showing different appendiceal positions including retrocecal, pelvic, and subcecal variants with the expected pain location and examination findings for each position. Panel C: A CT scan demonstrating appendicitis with appendiceal diameter of twelve millimeters, appendicolith visible at the base, and surrounding inflammatory fat stranding. Panel D: A treatment algorithm for appendicitis based on presentation complexity showing uncomplicated cases proceeding to laparoscopic appendectomy, abscess cases managed with antibiotics plus drainage followed by interval appendectomy, and peritonitis requiring emergent surgery.</image>

VIII. Biliary Disease

Biliary colic results from transient obstruction of the cystic duct by a gallstone, causing gallbladder distension against the obstructing stone and visceral pain that is typically steady rather than truly colicky despite the name. The pain is located in the right upper quadrant or epigastrium, often radiates to the right scapula or shoulder, and typically lasts thirty minutes to several hours before resolving spontaneously as the stone disimpacts or passes. Episodes are often precipitated by fatty meals that stimulate cholecystokinin release and gallbladder contraction. Physical examination during an episode may reveal mild right upper quadrant tenderness without peritoneal signs, fever, or leukocytosis. Laboratory studies are normal, distinguishing biliary colic from cholecystitis and choledocholithiasis.

Acute cholecystitis develops when cystic duct obstruction persists, leading to gallbladder wall inflammation, edema, and potentially ischemia, necrosis, and perforation if untreated. The pain is constant rather than episodic, lasting more than six hours, and is accompanied by fever, right upper quadrant tenderness with Murphy's sign, and leukocytosis. Laboratory studies may show mild elevation of liver enzymes. Ultrasound is the initial imaging study of choice, demonstrating gallstones, gallbladder wall thickening greater than three millimeters, pericholecystic fluid, and sonographic Murphy's sign. Hepatobiliary iminodiacetic acid scan may be used when ultrasound is equivocal, with non-visualization of the gallbladder indicating cystic duct obstruction. Treatment is cholecystectomy, ideally performed laparoscopically within seventy-two hours of symptom onset. Patients who are poor surgical candidates may be managed with percutaneous cholecystostomy for drainage.

Choledocholithiasis refers to stones in the common bile duct, either passing from the gallbladder through the cystic duct or less commonly forming primarily in the bile duct. Clinical presentation includes biliary-type pain with jaundice, and laboratory studies show elevated bilirubin and alkaline phosphatase with variable transaminase elevation. Ultrasound may demonstrate common bile duct dilation greater than six millimeters, though the stone itself is often not visualized. Management includes endoscopic retrograde cholangiopancreatography for stone extraction followed by cholecystectomy, or laparoscopic cholecystectomy with intraoperative cholangiography and laparoscopic common bile duct exploration. The choice depends on local expertise and probability of common duct stones.

Acute cholangitis represents infection of the biliary tree, typically resulting from biliary obstruction with bacterial overgrowth, and constitutes a surgical emergency requiring urgent biliary decompression. The classic Charcot's triad of fever, right upper quadrant pain, and jaundice is present in only fifty to seventy percent of patients. Reynolds' pentad adds altered mental status and hypotension, indicating severe sepsis requiring more urgent intervention. Common organisms include Escherichia coli, Klebsiella, Enterococcus, and anaerobes. Treatment requires intravenous antibiotics covering these organisms combined with urgent biliary drainage, typically via ERCP with sphincterotomy and stone extraction or stent placement if complete stone clearance is not possible. Percutaneous transhepatic cholangiography provides an alternative drainage route when ERCP fails or is not available.

<image>Panel A: A spectrum diagram showing the progression of biliary disease from asymptomatic gallstones to biliary colic with transient obstruction, acute cholecystitis with persistent obstruction and inflammation, and complicated cholecystitis with gangrene or perforation. Panel B: An ultrasound image demonstrating acute cholecystitis with gallbladder wall thickening measured at five millimeters, pericholecystic fluid collection, and multiple echogenic gallstones with posterior acoustic shadowing. Panel C: A comparison diagram distinguishing biliary colic, cholecystitis, and choledocholithiasis based on pain duration, fever, laboratory findings, and ultrasound findings. Panel D: An ERCP image showing choledocholithiasis with a stone in the common bile duct being extracted using a balloon catheter after sphincterotomy.</image>

IX. Bowel Obstruction

Small bowel obstruction occurs when mechanical blockage prevents normal passage of intestinal contents, with adhesions from previous surgery accounting for approximately sixty percent of cases in developed countries. Other causes include incarcerated hernias, malignancy, Crohn's disease, and less commonly intussusception, gallstone ileus, and foreign bodies. The clinical presentation includes cramping abdominal pain that comes in waves as the bowel contracts against the obstruction, nausea and vomiting which is early and bilious in proximal obstruction or late and feculent in distal obstruction, abdominal distension, and obstipation. Physical examination reveals distended abdomen with high-pitched, hyperactive bowel sounds in early obstruction progressing to absent sounds as the bowel becomes atonic.

The distinction between partial and complete obstruction, and between simple obstruction and strangulation, guides management decisions. Partial obstruction allows passage of some gas and liquid, with patients often continuing to pass flatus and even have diarrhea. Complete obstruction prevents all passage with absolute constipation and more rapid progression to complications. Strangulation occurs when the obstructed bowel segment has compromised blood supply, leading to ischemia, necrosis, and perforation if not promptly addressed. Clinical signs suggesting strangulation include constant rather than colicky pain, fever, tachycardia, peritoneal signs on examination, and metabolic acidosis with elevated lactate on laboratory studies. CT findings suggestive of strangulation include mesenteric haziness, bowel wall thickening or pneumatosis, and reduced or absent wall enhancement.

Conservative management is appropriate for partial small bowel obstruction without signs of strangulation. This includes nothing by mouth, nasogastric tube decompression, intravenous fluid resuscitation and electrolyte correction, and serial abdominal examinations. Water-soluble contrast administered orally or via nasogastric tube serves both therapeutic and prognostic purposes, with contrast reaching the colon within twenty-four hours predicting resolution with conservative management. Failure to progress on serial examinations or contrast study, development of signs concerning for strangulation, or complete obstruction that does not resolve mandates surgical intervention. Surgery involves exploration, identification of the point of obstruction, adhesiolysis or reduction of hernia, and assessment of bowel viability with resection of nonviable segments.

Large bowel obstruction differs from small bowel obstruction in etiology, presentation, and management. Malignancy, primarily colorectal adenocarcinoma, accounts for approximately sixty percent of large bowel obstructions. Other causes include volvulus, diverticular stricture, and fecal impaction. The presentation features prominent abdominal distension with late vomiting compared to small bowel obstruction. A critical concern is the competent ileocecal valve, present in approximately sixty percent of patients, which creates a closed-loop obstruction with the cecum being the site of maximal wall tension per Laplace's law. Cecal diameter exceeding twelve centimeters on imaging indicates high risk of perforation. CT provides definitive diagnosis including the level and likely cause of obstruction. Treatment depends on the cause, with sigmoid volvulus often amenable to endoscopic decompression followed by elective sigmoid resection, while obstructing colorectal cancer may require emergent resection or colonic stenting as a bridge to surgery.

<image>Panel A: An abdominal radiograph demonstrating small bowel obstruction with multiple dilated loops of small bowel, air-fluid levels at different heights on upright view, and decompressed colon. Panel B: A CT scan showing small bowel obstruction with dilated proximal small bowel measuring five centimeters, decompressed distal bowel, and a clear transition point at an adhesive band. Panel C: A flowchart for small bowel obstruction management showing initial conservative management with NGT and IV fluids, water-soluble contrast challenge, assessment for resolution versus progression, and indications for operative intervention. Panel D: An abdominal radiograph demonstrating sigmoid volvulus with the classic coffee bean sign showing a markedly dilated sigmoid colon arising from the pelvis with convergence of the walls toward the point of torsion.</image>

X. Initial Management and Resuscitation

Initial assessment and resuscitation of the patient with acute abdomen follow standard principles of airway, breathing, and circulation while simultaneously gathering diagnostic information. Hemodynamically unstable patients require immediate resuscitation with large-bore intravenous access and crystalloid fluid administration while emergent surgical consultation is obtained. Patients who are hypotensive, tachycardic, febrile with signs of sepsis, or have peritonitis on examination may require resuscitation in an intensive care setting. Laboratory studies including complete blood count, metabolic panel, lactate, coagulation studies, and type and screen should be obtained early. Foley catheter placement allows monitoring of urine output as a measure of resuscitation adequacy.

Nasogastric tube decompression is indicated for patients with vomiting, abdominal distension suggesting obstruction, or when bowel rest and decompression will aid in management. Adequate decompression reduces the risk of aspiration, relieves distension-related discomfort, and facilitates physical examination. Intravenous fluids should be administered to correct volume deficits from third-spacing, vomiting, or decreased oral intake, with initial crystalloid boluses followed by maintenance fluids with electrolyte supplementation as needed. Patients with bowel obstruction may have significant potassium and chloride deficits requiring replacement.

Appropriate antibiotic therapy should be initiated early when infection is suspected or peritoneal contamination has occurred. For appendicitis and cholecystitis, coverage should include gram-negative enteric organisms and anaerobes, with typical regimens including ceftriaxone plus metronidazole or piperacillin-tazobactam as single-agent therapy. Diverticulitis treatment traditionally included ciprofloxacin plus metronidazole, though piperacillin-tazobactam or ertapenem provide broader coverage for complicated cases. Perforated viscus and peritonitis require broad-spectrum coverage including anti-pseudomonal agents. Cholangitis requires coverage for biliary pathogens including Escherichia coli, Klebsiella, and Enterococcus, typically with piperacillin-tazobactam or a carbapenem. The duration of antibiotic therapy depends on the source control achieved and clinical response.

Pain management should not be withheld pending diagnosis, as adequate analgesia does not interfere with diagnostic accuracy and improves patient comfort and cooperation with examination. Intravenous opioids such as morphine or fentanyl provide effective analgesia and can be titrated to effect. Serial abdominal examinations after adequate analgesia may actually be more reliable than examination of a patient in severe distress. Surgical consultation should be obtained emergently for patients with peritonitis, pneumoperitoneum, hemodynamic instability, or clinical findings concerning for strangulated bowel. Urgent consultation is appropriate for patients with appendicitis, cholecystitis, bowel obstruction not resolving with conservative management, and other conditions likely to require operative intervention.

<image>Panel A: An initial resuscitation protocol flowchart for acute abdomen showing parallel pathways for hemodynamic assessment with fluid resuscitation, airway management, nasogastric decompression, laboratory studies, and imaging, with decision points for surgical consultation based on findings. Panel B: A table of antibiotic selection for acute abdominal conditions showing recommended regimens for appendicitis, cholecystitis, diverticulitis, perforation, and cholangitis with organisms targeted by each regimen. Panel C: An illustration of nasogastric tube placement technique showing patient positioning, tube measurement from nose to ear to xiphoid, and confirmation of placement by aspiration and auscultation. Panel D: A surgical urgency classification diagram showing emergent conditions including peritonitis and hemodynamic instability, urgent conditions including appendicitis and cholecystitis, and conditions appropriate for non-emergent evaluation, with expected timing for surgical consultation and intervention.</image>

Summary

• Acute abdomen requires systematic evaluation to differentiate surgical from non-surgical causes, with emphasis on identifying conditions requiring emergent intervention
• Pain characteristics including visceral versus parietal quality, location, onset, and migration provide important diagnostic information
• Red flags requiring urgent surgical evaluation include peritonitis, hemodynamic instability, rigid abdomen, and severe pain disproportionate to examination findings
• CT with intravenous contrast is the primary imaging modality for most acute abdominal conditions, with ultrasound preferred for biliary disease and in pregnant patients
• Appendicitis classically presents with periumbilical pain migrating to the right lower quadrant, with laparoscopic appendectomy as definitive treatment for uncomplicated cases
• Acute cholecystitis is characterized by Murphy's sign, ultrasound findings of wall thickening and pericholecystic fluid, and is treated with cholecystectomy
• Cholangitis presenting with Charcot's triad requires urgent biliary decompression via ERCP combined with intravenous antibiotics
• Small bowel obstruction is most commonly caused by adhesions, with conservative management including NGT decompression for partial obstruction and surgery for complete obstruction or signs of strangulation
• Diverticulitis is classified by Hinchey staging, with uncomplicated cases managed with antibiotics and complicated cases requiring drainage or surgery
• Initial management includes resuscitation, appropriate antibiotics, pain control, and timely surgical consultation based on clinical findings

Key Terms

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