CT of diverticulitis and alternative conditions

CT of Diverticulitis and Alternative Conditions Patrick M. Rao The clinical diagnosis of diverticulitis is often uncertain and frequently incorrect. Diagnostic imaging such as w i t h helical CT offers a rapid and accurate diagnosis of diverticulitis and its complications as well as alternative conditions. In particular, helical CT combined with contrast material administered through the colon is highly accurate and can be obtained quickly. CT signs of diverticulitis include focal inflammatory wall thickening and paracolic inflammation superimposed on diverticular disease (diverticula, muscular wall hypertrophy). Common alternative conditions that can clinically mimic diverticulitis include small bowel obstruction, primary epiploic appendagitis, acute cholecystitis, appendicitis, ileitis, ovarian cystic disease, and ureteral stone disease. Early and frequent use of diverticular CT promises to improve diagnosis and treatment of patients with clinically suspected diverticulitis, Copyright © 1999 by W.B. Saunders Company

T OF ACUTE abdominal conditions has advanced both with the availability of helical (spiral) technology and recent development of imaging protocols designed for specific clinical concerns. Clinically suspected colonic diverticulitis can be rapidly and definitely confirmed or excluded; complications of diverticulitis, as well as alternative conditions, can also be readily identified. This article reviews the clinical diagnosis of diverticulitis, diagnostic imaging options, diverticular CT performance and interpretation, and alternative conditions that are encountered.

incorrect. Misdiagnosis rates of 34% to 67% have been reported in patients with surgical and pathological proof of diagnosis.2 Many patients medically treated for presumed uncomplicated diverticulitis actually have an alternative condition requiring different (or no) treatment. Patients with complications of diverticulitis that require interventional radiologic or surgical treatment often are conservatively managed until lack of improvement prompts further evaluation, usually with CT. Many investigators recommend early radiologic imaging of all patients with clinically suspected diverticulitis.2-5

CLINICAL DIAGNOSIS

DIAGNOSTIC IMAGING OPTIONS

Patients with acute colonic diverticulitis typically present with generalized malaise, left lower abdominal quadrant (LLQ) pain, fever, nausea, vomiting, anorexia, and change in bowel habits, particularly constipation. 1 On physical examination, LLQ tenderness to palpation, rebound and involuntary guarding may be present. Abdominal tenderness may be more midline or even in the right lower abdominal quadrant when the sigmoid colon is redundant. Laboratory analysis may show an elevated white blood cell count. Severity of the clinical findings depends in large degree on the extent of paracolic inflammation that has spread from the point of the inflamed diverticulum. Despite a characteristic constellation of clinical findings in many patients with diverticulitis, a diagnosis based solely on clinical criteria is often

Plain abdominal radiographs are of limited utility in patients with clinically suspected diverticulitis. In most cases of uncomplicated diverticulitis, plain radiographs will not show any findings. With complicated diverticulitis, pneumoperitoneum, portal venous gas, or an extraluminal air-fluid level may occasionally be noted. Large bowel obstruction can be suggested, when present. Until recently, barium or water-soluble contrast enema had been the primary imaging examination for patients with clinically suspected diverticulitis; in the acute setting, water-soluble enema has proved useful and safe for diagnosis.2,6,7Findings of diverticulitis noted at enema examination depend mainly on the secondary effects on the colonic lumen caused by the extramucosal manifestations of diverticulitis and include diverticula, muscular wall hypertrophy, intramural or extramural mass effect on the colonic lumen, large bowel obstruction, colonic foreshortening, and intramural tracking or intraperitoneal extravasation of contrast material.8-10 Contrast enema examinations generally show the presence of diverticular disease and findings suggesting diverticulitis. However, the full extent of

C

From the Department of Radiology, Massachusetts General Hospital, Boston, MA. Address reprint requests to Patrick M. Rao, MD, Division of Emergency Radiology, Department of Radiology, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. Copyright © 1999 by W.B. Saunders Company 0887-2171/99/2002-0005510.00/0 86

Seminars in Ultrasound, CT, and MRI, Vo120, No 2 (April), 1999: pp 86-93

CT OF DIVERTICULITIS AND ALTERNATIVE CONDITIONS

peritoneal involvement is usually underestimated and paracolic abscesses, for example, can be overlooked. Given the success of percutaneous diverticular abscess drainage both in lieu of surgery and before definitive surgical treatment, this is an important limitation of enema examination. 11,~2 Also, most alternative conditions unrelated to the colon are overlooked at contrast enema performed for suspected diverticulitis.i° In most centers, diverticular CT has replaced contrast enema examination for evaluating patients with clinically suspected diverticulitis. 8,1°,13 Conventional CT combined with oral and intravenous contrast material administration, as well as air insufflation of the rectum, has been reported to be up to 93% sensitive and 100% specific for diagnosing diverticulitis. 1° Another report of conventional CT with oral and intravenous contrast material administration cited a 79% accuracy rate for diverticular CT. 6 Several researchers have cited the value of air or contrast material administered through the colon for providing optimal colonic distention and opacification. 6,~°,I4,~5 HELICAl_ CT OF DIVERTICULITIS Helical CT combined with contrast material administered through the colon only has been recently reported to have 97% sensitivity, 100% specificity, 100% positive predictive value, 98% negative predictive value, and 99% overall accuracy for confirming or excluding diverticulitis.~6 In this investigation, alternative diagnoses were noted at CT in 58% of the patients who did not have diverticulitis. Advantages of this technique include high accuracy and nearly immediate scanning without the costs, risks, and discomforts of contrast material administered orally and intravenously.

87

viewed at the CT console for technical adequacy and preliminary interpretation. Images are filmed in soft-tissue (340 Hounsfield units [HU] window width, 40 HU window level) and lung (1500 HU window width, - 5 0 0 HU window level) window settings, where appropriate.

Diverticular CT Interpretation Familiarity with the CT appearances of the normal colon, colonic diverticulosis, and diverticulitis as well as common alternative conditions is required for accurate diverticular CT interpretations. The normal colon demonstrates a thin wall and haustrations, without diverticula (Fig 1). Findings of colonic diverticulosis at CT include diverticula (Fig 2), which appear as rounded outpouchings containing air and/or contrast material, and muscular wall hypertrophy (Fig 3), which appears as a sawtooth-like thickening of colonic haustrations. The hallmark of diverticulitis at CT is focal inflammatory wall thickening with paracolic inflammarion superimposed on diverticular disease (Figs 4, 5). Inflammatory changes include paracolic fat stranding, inflammatory mass (phlegmon) (Fig 6), extraluminal air bubbles (Fig 7), abscess (Fig 8), and dependent free fluid. 8,13,16 Extraluminal con-

Diverticular CT Performance Patients are placed in the left-side-down decubitus position on the CT table, a6 Between 400 and 600 mL of a 3% meglumine diatrizoate-saline solution (Gastrografin; Bristol-Meyers Squibb, Wallingford, CT) is infused through the colon via gravity drip through intravenous (IV) tubing and a soft rubber rectal catheter, without use of a balloon. Patients are turned supine and a digital abdominal radiograph is obtained. Helical scanning is performed from the diaphragm to the pubic symphysis with 5 mm collimation, 7.5 mm/sec table speed (1.5 pitch), and 7.5 mm image spacing. Images are

Fig 1. Normal sigmoid colon. CT image in a 41-year-old woman with a normal sigmoid colon (S).

88

PATRICK M. RAO

Fig 2. Diverticular disease. CT slice of a 70-year-old woman with multiple diverticula off the sigmoid colon (S),

trast material can be noted with sinus tract or fistula formation. Specific CT signs of diverticulitis also include the arrowhead sign (Fig 9) and the inflamed diverticulum (Figs 9 through 11). 17 The main advantage of contrast material administered through the colon is the rapid and consistent attainment of optimal colonic opacification and distention. Lumen opacificatiou helps identify and distinguish intraluminal from extraluminal air and fluid (abscess) collections (Fig 8). Lumen distention aids in distinguishing true from apparent wall thickening. It also helps identify and distinguish focal inflammatory wall thickening due to acute diverticulitis from underlying muscular wall hypertrophy (Fig 12).1°,16 Focal wall thickening superim-

Fig 3. Diverticular disease. CT slice of a 70-year-old man with muscular wall hypertrophy of the sigmoid colon (S). Diverticula were noted on other images (not shown).

Fig 4. Diverticulitis. CT image in a 47-year-old woman showing inflammatory wall thickening of the sigmoid colon (S), with adjacent fat stranding.

posed on muscular wall hypertrophy is a relatively specific CT sign in patients with clinically suspected diverticulitis. 16 Also, the arrowhead sign is most likely to be identified with good lumen distention (Figs 9, 13). 17 ALTERNATIVE CONDITIONS

In emergency department patients with clinically suspected diverticulitis, this diagnosis is often incorrect; one recent study cited a 43% rate of diverticulitis in patients imaged with CT with a leading clinical suspicion of diverticulitis36 Commonly encountered alternative conditions include

Fig 5. Diverticulitis. CT slice in a 34-year-old man with inflammatory wall thickening of the sigmoid colon (S), with adjacent fat stranding.

CT OF DIVERTICULITIS AND ALTERNATIVE CONDITIONS

89

Fig 8, Diverticular abscess. CT slice in a 64-year-old man with a paracolic abscess (A) due to perforated diverticulitis. Incidental note is made of a probable left renal cyst (C),

Fig 6. Diverticular phlegmon. CT slice of a 62-year-old woman showing a paracolic inflammatory mass (phlegmon, arrowheads) with a rim-calcified fecalith due to perforated diverticulitis.

small bowel obstruction, primary epiploic appendagitis, acute cholecystitis, appendicitis, ileitis, ovarian cystic disease, ureteral stone disease, perforated colon carcinoma, and perforated inflammatory bowel disease. The CT diagnosis of small bowel obstruction is usually straightforward. 18 Small-bowel loops, whether filled with air, gastrointestinal fluid, or contrast material, are seen to be distended (>3 cm in diameter) in a continuous fashion to the point of obstruction (Fig 14). Distal bowel loops are generally decompressed. Common causes of obstruction include adhesion, hernia, volvulus, intussuscep-

Fig 7. Perforated diverticulitis. CT image of a 66-year-old man with free air bubbles (arrow) due to perforated diverticulitis.

tion, intraluminal foreign body, and large-bowel obstruction; most of these are readily identified at CT. Primary epiploic appendagitis is an uncommon but underreported condition in which the draining appendageal vein of an epiploic appendage becomes thrombosed, leading to venous infarction of the appendage. For unknown reasons, sigmoid

Fig 9. Arrowhead sign and fecalith. CT image in a 67-yearold woman with diverticulitis showing an arrowhead sign (black arrow) and a calcified fecalith (white arrow) within an inflamed diverticulum.

90

Fig 10. Inflamed diverticulum. CT scan in a 71-year-old woman with diverticulitis showing an inflamed diverticulum (arrow).

colon appendages appear predisposed to torsion; these patients usually present to CT with a clinical suspicion of diverticulitis. At CT, a 2 to 3 cm, oval-shaped, fat-density, paracolic mass is noted, centered within inflammatory stranding (Fig 15).19,2° A central high-attenuating dot, thickened peritoneum, and subtle colonic wall thickening and compression may also be present. Patients with epiploic appendagitis require no treatment beyond pain control, and a CT diagnosis of epiploic appendagitis can avoid unnecessary hospitaliza-

Fig 11. Inflamed diverticulum. CT slice in a 62-year-old man with diverticulitis reveals an inflamed diverticulum (D).

PATRICK M. RAO

Fig 12. Subtle diverticulitis. CT image in a 19-year-old woman with diverticulitis shows mild inflammatory wall thickening (arrows), brought out to advantage by colonic contrast material.

tion, antibiotic therapy, and even surgery for this benign, self-limiting condition.21 Acute cholecystitis is occasionally encountered at CT in patients imaged for another clinical suspicion, such as appendicitis or diverticulitis. CT findings include a distended, thick-walled gallbladder with pericholecystic free fluid and fat stranding (Fig 16).22 Gallstones may also be noted. Mild cases of cholecystitis noted at CT should probably

Fig 13. Arrowhead sign. CT slice of a 52-year-old woman with diverticulitis reveals an arrowhead sign (arrow), brought out to advantage by colonic contrast material.

CT OF DIVERTICULITIS AND ALTERNATIVE CONDITIONS

91

Fig 14. Small bowel obstruction. CT scan of a 29-year-old woman shows multiple loops of dilated small bowel with air-fluid levels.

be confirmed with ultrasonography; CT is usually diagnostic in more severe cases. Acute appendicitis appears at CT as a distended appendix, periappendiceal inflammation and cecal apical changes. 23,24 As with diverticulitis, helical CT combined with contrast material administered through the colon has been shown to be highly accurate for diagnosing appendicitis. Particularly with a mobile cecum or a long, transversely

Fig 15. Primary epiploic appendagitis. CT image of a 65year-old woman shows an oval-shaped, fat-density paracolic mass (E) with adjacent fat stranding and thickened visceral and parietal peritoneum.

Fig 16. Acute cholecystitis. CT slice of a 47-year-old man with a thick-walled gallbladder (G} and adjacent fat stranding,

oriented appendix, appendicitis can clinically mimic diverticulitis (Fig 17). Ileitis appears at CT as small bowel loops with wall thickening, narrowed lumina, and adjacent fat stranding; free fluid and adenopathy are often associated findings (Fig 18). 25 Etiologies include infection, inflammation such as Crohn's disease, and ischemia. Pneumatosis intestinalis may be present in cases of small bowel ischemia. In women, an acute presentation of left-sided ovarian cystic disease can occasionally mimic diverticulitis. Intracyst hemorrhage may show a fluid-hemorrhage level. Cyst rupture may show low-density cyst fluid or high-density hemorrhage

Fig 17. Acute appendicitis. CT image in a 46-year-old man with a distended appendix (A) and focal cecal apical thickening (arrow).

92

PATRICK M. RAO

Fig 18, Ileitis. CT image of a 52-year-old man shows a loop of ileum w i t h a thickened wall.

in the paracolic gutter and/or pouch of Douglas. 26 Ovarian torsion may be inferred by the presence of an ovarian cyst or mass, which can predispose the ovary to torsion (Fig 19). CT findings with acute ureteral obstruction due to stone disease include direct visualization of a stone in the ureter (Fig 20), ureteral dilatation, perinephric stranding and fluid, renal enlargement and hypodensity, and one or more renal stones. 27,2s Stone size, density, location, number, degree of ureteral obstruction, and renal stone burden are readily determined. The presence of bowel contrast material in no way interferes with CT detection of ureteral stones. Perforated colon carcinoma can clinically mimic diverticulitis and can also be difficult to differentiate at CT from diverticulitis. Generally, a tumor mass shows large size, lobulation, and abrupt

Fig 20. Ureteral stone. CT scan in a 50-year-old man with a 5 mm distal ureteral stone causing ureteral obstruction. Note prominent rim sign (arrow),

margination; and metastases may be present. 29 Absence of underlying diverticular disease is helpful, although 20% of patients with sigmoid carcinoma have concomitant diverticular disease. 3° Mesenteric inflammation (fluid at the root of the mesentery or engorgement of sigmoid mesenteric vessels), an inflamed diverticulum, or an arrowhead sign, when present, can add specificity to an inflammatory mass due to diverticulitis. 17,31 Occasionally, follow-up imaging or colonoscopy with biopsy is required for definitive diagnosis. Inflammatory bowel disease such as Crohn's disease can mimic diverticulitis both clinically and at CT, with focal colonic wall thickening and adjacent inflammation. Practically speaking, most cases of Crohn's colitis involving the sigmoid colon will have associated changes elsewhere in the small and large bowel, particularly the terminal ileum. Underlying diverticular disease is also absent in many of these cases. Occasionally, follow-up imaging or colonoscopy with biopsy is required for definitive diagnosis. SUMMARY

Fig 19. Ovarian torsion, CT scan of a 51-year-old woman w i t h an enlarged ovarian cyst (O) that predisposed to ovarian torsion.

Helical CT, particularly with contrast material administered through the colon, offers a rapid and accurate way to confirm or exclude the diagnosis of diverticulitis. Complications requiring alterations in treatment are readily identified, and alternative conditions that can clinically mimic diverticulitis are usually diagnosed. Earlier and more frequent use of diverticular CT is likely in the future.

CT OF DIVERTICULITIS AND ALTERNATIVE CONDITIONS

93

REFERENCES

1. Pohlman T: Diverticulitis. Gastroenterol Emerg 17:357385, 1988 2. Wexner SD, Dailey TH: The initial management of left lower quadrant peritonitis. Dis Colon Rectum 29:635-638, 1986 3. Diner WC, Barnhard HJ: Acute diverticulitis. Semin Roentgenol 8:415-43l, 1973 4. Doris PE, Strauss RW: The expanded role of the barium enema in the evaluation of patients presenting with acute abdominal pain. J Emerg Med 3:93-100, 1985 5. Gottesman L, Zevon SJ, Brabbee GW, et al: The use of water-soluble contrast enemas in the diagnosis of acute iower left quadrant peritonitis. Dis Colon Rectum 27:84-88, 1984 6. Johnson CD, Baker ME, Rice RP, et al: Diagnosis of acute colonic diverticulitis: Comparison of barium enema and CT. AIR Am J Roentgenol 148:541-546, 1987 7. Kourtesis GJ, Williams RA, Wilson SE: Acute diverticulitis. Safety and value of contrast studies in predicting need for operation. Aust N Z J Surg 58:801-804, 1988 8. Hulnick DH, Megibow AJ, Balthazar EJ, et al: Computed tomography in the evaluation of diverticulitis. Radiology 152: 491-495, 1984 9. Greenall MJ, Levine AW, Nolan DJ: Complications of diverticular disease: A review of the barium enema findings. Gastrointest Radiol 8:353-358, 1983 10. Cho KC, Morehouse HT, Alterman DD, et al: Sigmoid diverticulitis: Diagnostic role of CT~comparison with barium enema studies. Radiology 176:111-115, 1990 11. Neff CC, vanSonnenberg E, Casola G, et al: Diverticular abscesses: Percutaneous drainage. Radiology 163:15-18, 1987 12. Saini S, Mueller PR, Wittenberg J, et al: Percutaneous drainage of diverticular abscess. Arch Surg 121:475-478, 1986 13. Doringer E: Computerized tomography of colonic diverticulitis. Crit Rev Diagn Imag 33:421-435, 1992 14. Neff CC, vanSonnenberg E: CT of diverticulitis: Diagnosis and treatment. Radiol Clin North Am 27:743-752, 1989 15. Labs JD, Sarr MG, Fishman EK: Complications of acute diverticulitis of the colon: Improved early diagnosis with computed tomography. Am J Surg 155:331-335, 1988 16. Rao PM, Rhea JT, Novelline RA, et al: Helical CT with only colonic contrast material for diagnosing diverticulitis: Prospective evaluation of 150 patients. AJR Am J Roentgenol 170:1445-1450, 1998 17. Rao PM, Rhea JT: Colonic diverticulitis: Evaluation of the arrowhead sign and the inflamed diverticulum for CT diagnosis. Radiology 209:775-780, 1998

18. Maglinte DD, Reyes BL, Harmon BH, et al: Reliability and role of plain film radiography and CT in the diagnosis of small bowel obstruction. AJRAm J Roentgenol 167;1451-1455, 1996 19. Rioux M, Langis P: Primary epiploic appendagitis: Clinical, US and CT findings in 14 cases. Radiology 191:523526, 1994 20. Rao PM, Wittenberg J, Lawrason JN: Primary epiploic appendagitis: Evolutionary changes in CT appearance. Radiology 204:713-717, 1994 21. Rao PM, Rhea JT, Wittenberg J, Warshaw AL: Misdiagnosis of primary epiploic appendagitis. Am J Surg 176:81-85, 1998 22. Kane RA, Costello R Duszlak E: Computed tomography in acute cholecystitis: New observations. AJR Am J Roentgenol 141:697-701, 1983 23. Rao PM, Rhea JT, Novelline RA, et al: Helical CT scanning combined with contrast material administered only through the colon for imaging of suspected appendicitis. AJR Am J Roentgenol 169:1275-1280, 1997 24. Rao PM, RheaJT, Novelline RA: Sensitivity and specificity of the individual CT signs of appendicitis: experience with 200 helical appendiceal CT examinations. J Comput Assist Tomogr 21:686-692, 1997 25. Rao PM, Rhea J, Novelline RA: CT diagnosis of mesenteric adenitis. Radiology 202:145-149, 1997 26. Rao PM, Turner MA: Right lower quadrant pain: Imaging with computed tomography. Emerg Radiol 2:345-366, 1995 27. Smith RC, Verga M, McCarthy S, et al: Diagnosis of acute flank pain: Value of unenhanced helical CT. AJR Am J Roentgenol 166:97-101, 1996 28. Smith RC, Verga M, Dalrymple N, et al: Acute ureteral obstruction: Value of secondary signs of helical unenhanced CT. AJRAm J Roentgenol 167:1109-1113, 1996 29. Hulnick DH, Megibow AJ, Balthazar EJ, et al: Perforated colorectal neoplasms: Correlation of clinical, contrast enema, and CT examination. Radiology 164:611-615, 1987 30. Morton DL, Goldman L: Differential diagnosis of diverticulitis and carcinoma of the sigmoid colon. Am J Surg 103:55-60, 1962 31. Padidar AM, Jeffrey RB, Mindelzun RE, Dolph JF: Differentiating sigmoid diverticulitis from carcinoma on CT scans: Mesenteric inflammation suggests diverticulitis. AJR Am J Roentgenol 163:81-83, 1994