- Email: [email protected]
Perforated Appendicitis: Assessment With Multidetector Computed Tomography
Perforated Appendicitis: Assessment With Multidetector Computed Tomography Francesca Iacobellis, MD,*,† Isabella Iadevito, MD,* Federica Romano, MD,* Michele Altiero, MD,* Bikram Bhattacharjee, MD,‡ and Mariano Scaglione, MD*,‡ Appendicitis is one of the most common abdominal surgical emergencies. In some cases, the correct diagnosis may be challenging, owing to different conditions that can mimic this pathology. In this context, abdominal computed tomography (CT) is the imaging modality of choice, leading to an accurate diagnosis and to a reduction in unnecessary laparotomies. The diagnosis of perforated appendix is crucial, but the detection of the perforation signs by CT may not be so simple in the early process. The aim of this article is to review the multiple detector CT signs of perforated appendicitis. Semin Ultrasound CT MRI 37:31-36 C 2016 Elsevier Inc. All rights reserved.
Introduction
A
limentary tract perforations constitute an emergency condition requiring prompt diagnosis and surgical treatment.1,2 The diagnosis depends on clinical suspicion and especially on imaging tests that permit defining the presence, the level and cause of perforation.3-8 Appendicitis is the most common cause of acute abdomen and the most common acute condition requiring surgery.9,10 The vermiform appendix, usually located to the right side at the apex of the cecum, at the junction of the 3 taeniae coli, can be considered as a true diverticulum of the cecum as it has all of the layers of the colonic wall: mucosa, submucosa, muscularis (longitudinal and circular), and the serous. The appendix may be detected in a various range of positions on imaging examinations owing to its variable course. Retrocecal is the most common (Fig. 1); alternative routes are retroileal, preileal, pelvic, cross midline, and also into the hepatorenal recess.11-13 Left-sided appendicitis may be rarely found in patients with congenital intestinal malrotation and situs inversus.14 The appendix may have a variable length, ranging from 5-35 cm and average of *Department of Diagnostic Imaging, Pineta Grande Medical Center, Castel Volturno, Italy. †Department of Radiology, Second University of Naples, Naples, Italy. ‡Department of Radiology, Darent Valley Hospital, Dartford & Gravesham NHS Trust, Dartford, UK. Address reprint requests to Francesca Iacobellis, MD, via Domitiana Km 30.000, 81030 Castel Volturno CE, Italy. E-mail: [email protected]
http://dx.doi.org/10.1053/j.sult.2015.10.002 0887-2171/& 2016 Elsevier Inc. All rights reserved.
9 cm.11,15 The risk of developing acute inflammation of the appendix in the lifetime is approximately 7%,10 mostly involving patients from 10-30 years16; there is a slight predilection for male gender.17 Mortality and morbidity rates related to surgical intervention for appendicitis are 0.24% and 6.1%, respectively, and 1.7% and 19% for perforated appendicitis.17 Signs and symptoms may depend on the inflammatory stage of the appendicitis and on the anatomical location of the appendix.11,18 Usually the clinical presentation is characterized by abdominal pain in the right inferior quadrant, nausea, vomiting, fever, anorexia, and laboratory leucocytosis.19 The pathophysiology of acute inflammation largely depends on luminal obstruction; other contributing processes are viral infections, poor diet, ischemia, and trauma.16,18 Luminal obstruction may be due to appendicolith (450% of cases) (Fig. 2), lymphoid hyperplasia of the appendix wall, foreign bodies, parasites, neoplasia, and metastasis.18 Following the obstruction, there is a lumen distension with an increase of endoluminal pressure and, in less vascularized wall area, this is responsible for a further reduction in the arterial blood flow, leading to perforation due to ischemic necrosis of the wall.18 In 80% of cases, the typical clinical picture and the laboratory data lead to the correct diagnosis, and in approximately 20% of cases the findings can be atypical and subtle, with a large variety of sign and symptoms, and the differential diagnosis may be challenging, especially in young female patients and in the elderly people.18 31
F. Iacobellis et al.
32
A
C
B
Figure 1 Appendicitis. MDCT axial scans (A) and (B) and coronal MPR image (C) show a distended, thickened wall (11 mm) inflamed appendix, with a slightly increased wall enhancement and stratification (arrow). There is stranding of the adjacent perivisceral fat with multiple lymphoadenopathies and a fluid around the appendix (arrowhead). Free fluid in the right parietocolic recess is also seen (asterisk in C). MPR, multiplanar reconstructions.
Imaging plays a crucial role when the clinical presentation is atypical and differential diagnosis mimicking appendicitis needs to be excluded.20 The available imaging modalities include ultrasound (US), multidetector computed tomography (MDCT), and magnetic resonance imaging. US is the first imaging test, particularly in patients with mild abdominal pain and women. Abdominal CT with intravenous contrast medium (IVCM) is now considered the standard of care.16,21 It is firstly required in patients with acute abdomen and atypical clinical presentation of appendicitis and suspected perforation.10,22 Owing to the high sensitivity (87%-99%) and specificity (92%-99%), it is the imaging modality of choice for an accurate diagnosis and to reduce unnecessary laparotomies.9,18,20 Furthermore, in adult patients clinically suspected for an appendicitis, CT may identify an alternative cause for symptoms, which often requires hospitalization and surgery for treatment.23 Magnetic resonance examination, if available in emergency setting, is the first choice in pregnant women.10 This review is particularly focused on the MDCT assessment of perforated appendicitis.
A
MDCT Imaging MDCT is considered the most valuable imaging technique in the identification of presence, site, and cause of alimentary tract perforations and some authors consider CT as the primary technique for the diagnosis of acute abdominal pain.2–8,24,25 Prompt diagnosis of perforated appendicitis is important considering the surgical implications and complications.
Study Protocol In the era of MDCT, all the examinations have to be performed with a high-resolution protocol, with slice thickness and a reconstruction interval values of approximately 1 mm, completed by multiplanar reconstructions. In our institution all examinations are acquired by a 128 slices dual-source CT system (Siemens Somatom Definition Flash), with slice thickness of 1.2 mm, collimation of 2 128 0.6 mm3, and rotation time of 0.28 seconds. The protocol includes IVCM administration with scans acquisition from the dome of the diaphragm to the symphysis pubis. Enteric contrast agent is
B
Figure 2 Perforated appendicitis. Sagittal MPR image (A) and MDCT axial scan (B) show a tortuous, fluid-dilated appendix with increased wall enhancement (arrow). Note also some endoluminal appendicolithes and air gas bubbles. Free fluid is seen around the cecum (asterisk in A). MPR, multiplanar reconstructions.
CT of perforated appendicitis
A
33
B
C
Figure 3 Perforated appendicitis. MDCT axial scan (A) and coronal MPR images (B and C) show inflamed appendix (arrow), distended by fluid with parietal hyperenhancement and an appendicolith within the lumen. A parietal defect can be appreciated in the distal part, where an extraluminal air loculus is also seen (C). A large fluid collection in the right iliac fossa is also visible (arrowhead). MPR, multiplanar reconstructions.
not administered. The IVCM, 80-100 mL of iodinated contrast agent at 400 mg/mL concentration injected at 3-4 mL/s followed by 50 mL of saline injected at the same flow-rate, is necessary to enhance the bowel walls and solid organs. An automated bolus tracking, with region of interest placed in the descending aorta at an attenuation threshold of 100 HU, may be used to time the beginning of the arterial phase, if retained depending on the clinical suspicion. The study of the bowel wall is optimal in the portal phase (70-second delay from the end of injection). To identify and to display the appendix in its length, 3-dimensional multiplanar reconstruction are useful.
CT Findings When approaching the abdominal CT of patients with acute abdomen from suspected appendicitis it is important to
A
B
correctly identify the cecum and it should not be assumed that the appendix is normal if it is not seen in the right lower quadrant, as some congenital anomalies are related with leftsided appendix.14 The position of the base of the appendix is relatively constant, between the ileocecal valve and the apex of the cecum, and this relationship is maintained even when the cecum is mobile. The location of the tip of the appendix may be more variable, as described earlier, and it is important to explore the appendix in its whole length as it is possible to develop inflammation confined to the distal portion of the appendix, a condition known as “tip appendicitis.”16 The cecum has to be examined even if in the clinical history of the patients a previous appendectomy is reported, as it is possible to develop inflammation of even the residual appendix after a prior incomplete appendectomy. This is known as “stump” appendicitis.16,26 In normal condition the maximum diameter of the appendix (wall to wall) is 0.6 cm with a wall thickness of approximately 0.1 cm, the lumen may contain fluid or gas, and the
C
Figure 4 Perforated appendicitis. MDCT axial scan (A) and coronal MPR images (B and C) show hyperenhancement of the appendiceal wall, thickened and distended by fluid that appears located caudally to the cecum (arrow). A hyperdense appendicolith is seen in the lumen (C) as well as multiple millimetric air loculi (B); furthermore, enhancing defect foci of the wall are seen. There is stranding of the periappendicular mesenteric fat with free fluid surrounding the appendix (arrowhead). MPR, multiplanar reconstructions.
F. Iacobellis et al.
34 surrounding mesenteric fat tissue appears homogeneous. Appendicoliths may be seen in a noninflamed appendix too.27 Main signs of appendix inflammation include: – – – – – – –
enlarged lumen, wall thickening, alterations of the parietal enhancement, “arrowhead” sign, surrounding fat alteration, abscess formation, and inflammation of adjacent organs.10,18
Owing to the appendiceal obstruction and to the mucosal continuous secretion, the lumen of the inflamed appendix become enlarged with a wall-to-wall caliber wider than 0.6 cm (Figs. 1, 2, and 4). In the early stages of the inflammation there is an increase in the blood supply with wall hyperemia (hyperenhancement) and thickening of the wall of the appendix that becomes more than 0.2 mm (Figs. 1-4). The “arrowhead” sign is a focal symmetric thickening of the cecal wall near the appendiceal base that may be seen when oral or rectal (or both) intraluminal contrast is administered. It has a low sensitivity (30%) but high specificity (100%).28 In response to the inflammatory reaction, the adipose tissue surrounding the appendix increases in density and appears as “dirty fat” sign29 (Figs. 1 and 4). If there is a progression in the pathology, and the lumen becomes overdistended, it causes an impairment in the blood supply to the wall with the evidence of reduced vascularization area and ischemic parietal zone formation (hypoattenuating after IVCM) (Figs. 3 and 4). This process leads to perforation of the appendix, which is a condition requiring surgery (Figs. 1-5). The periappendicular reaction increases (Fig. 1) and the leak of enteric material causes the development of a local phlegmon, without a clear wall, usually detected at the apex of the appendix. When the phlegmon acquires a definite thick wall, showing peripheral enhancement after IVCM administration, it is a clear sign of progression into abscess (Fig. 5).
A
B
In more advanced cases, an involvement of contiguous tissues and organs in the inflammatory-infectious process may be seen, with free fluid detection in the peritoneum related to the inflammatory response18 (Figs. 1, 2, and 4). Based on anatomopathologic findings, appendicitis can be classified as follows: – catharral appendicitis when inflammation is limited to the mucosal layer, – phlegmonous appendicitis when the wall is more involved in the inflammatory process with the progressive development of intraparietal microscopic phlegmon presence, and – gangrenous appendicitis when there is an extensive necrosis of the wall. Perforation of the appendix is not easy to detect; a study evaluating CT sensitivity for perforation in the pediatric population found it to be approximately 62%.30 Especially at the beginning of the process the signs are subtle; otherwise, when the perforation has been present for some time, the phlegmon or abscess might completely obscure the perforated appendix.16 However, the diagnosis of perforated appendix is crucial as perforation increases the risk complication after surgery. The most specific signs related to perforated appendix are the following. – Abscess presence is considered to be the most specific sign of perforation and it represents the most frequent complication of perforated appendicitis. – Detection of foci defects in the wall has a high sensitivity of 95%, a specificity of 97%, and an accuracy of 96%. – Phlegmon presence has reported specificity of 95% but low sensitivity (40%). – Extraluminal air appears as the presence of bubble gas outside the appendix. This sign is highly (98%) specific but has low sensitivity of 22%-35%. – Finding of extraluminal appendicolith is also highly (100%) specific, but poorly (32%) sensitive.18 The
C
Figure 5 Perforated appendicitis. MDCT MPR in coronal (A), axial (B), and sagittal (C) planes show a retrocecal thickened perforated appendix (A: arrow) with a contiguous air-fluid collection (A-C: arrowhead) in which a hyperdense appendicolith (A-C: curved arrow) is seen. There is stranding of the periappendicular mesenteric fat with multiple lymphoadenopathies (B: circle). MPR, multiplanar reconstructions.
CT of perforated appendicitis presence of appendicolith may accelerate the occurrence of perforation.14 The most frequent complications of perforated appendix are represented by abscess formation and peritonitis. The development of peritonitis secondary to perforation is more frequent in children due to rapid progression from inflammation to wall rupture. In adults, the inflammatory adhesions developing around the site of inflammation try to arginate the inflammatory process, leading more frequently to phlegmons and abscesses formation instead of a rapid evolution in peritonitis.14 Other complications that may be detected in the abdominal cavity following appendix perforation are pylephlebitis and pylethrombosis related to ascending infection along the mesenteric portal venous system; ureteral reactive involvement with different grades of hydroureteronefrosis; gangrenous appendicitis; dynamic or mechanical bowel obstruction due to the bowel reaction to the inflammation or to the narrowing of the terminal ileum in relationship with periappendicular inflammatory reaction; and fistula with other contiguous organs such as bladder, vagina, uterus, and skin.14
Differential Diagnosis In acute settings, it is important to differentiate other entities from appendicitis because some of the other conditions can be managed conservatively.12 The most frequent pathologic conditions that must be differentiated from the appendicitis are: – pathologies starting from the appendix such as appendiceal diverticulitis, appendiceal mucocele (due to chronic obstruction in absence of acute inflammation or due to benign or malignant neoplasms); and primary neoplasms of the appendix31,32; – pathologies with secondary involvement of the appendix such as enterocolitis, cecal diverticulitis, and Crohn's disease; and – pathologies that mimic appendicitis such as bowel obstruction, intussusceptions, acute cholecystitis, perforated duodenal ulcer, Meckel's diverticulitis, colonic diverticulitis, pancreatitis, right renal colic or pyelonephritis, epiploic appendagitis, mesenteric adenitis, and gynecologic processes such as functional ovarian cyst bleeding, ovarian torsion, salpingitis or pelvic inflammatory disease, ectopic pregnancy, pyosalpinx, tuboovarian abscess, and endometriosis.18,33
Conclusion Acute appendicitis is a frequent pathology that is clinically diagnosed usually, but in some cases the diagnosis may be challenging. MDCT, owing to its high sensitivity and specificity, is the imaging modality of choice to make an accurate diagnosis among the different surgical conditions that need to be differentiated from acute appendicitis, to avoid the
35 complications related to the perforation, detecting the early signs of inflammation, or to identify the sign of perforation suggesting a prompt surgical intervention. MDCT can also reduce unnecessary laparotomies, allowing to correctly manage patients with medical condition mimicking acute appendicitis.
References 1. Del Gaizo AJ, Lall C, Allen BC, et al: From esophagus to rectum: A comprehensive review of alimentary tract perforations at computed tomography. Abdom Imaging 39:802-823, 2014 2. Iacobellis F, Berritto D, Grassi R: Diagnostic approach to alimentary tract perforations. In: Romano L, Pinto A (eds): Imaging of Alimentary Tract Perforation. Springer: International Publishing Switzerland; 1-7, 2015 3. Furukawa A, Sakoda M, Yamasaki M, et al: Gastrointestinal tract perforation: CT diagnosis of presence, site, and cause. Abdom Imaging 30:524-534, 2005 4. Pinto A, Scaglione M, Giovine S, et al: Comparison between the site of multislice CT signs of gastrointestinal perforation and the site of perforation detected at surgery in forty perforated patients. Radiol Med 108(3):208-217, 2004 5. Pinto A, Grassi R, Rossi G, et al: Computerized tomography in the study of jejuno-ileal perforations. Personal case load. Radiol Med 96(6):602-606, 1998 6. Grassi R, Romano S, Pinto A, et al: Gastro-duodenal perforations: Conventional plain film, US and CT findings in 166 consecutive patients. Eur J Radiol 50(1):30-36, 2004 7. Grassi R, Pinto A, Rossi G, et al: Conventional plain-film radiology, ultrasonography and CT in jejuno-ileal perforation. Acta Radiol 39 (1):52-56, 1998 8. Grassi R, Catalano O, Pinto A, et al: Case report: Identification of the transverse mesocolon and root of small bowel mesentery; a new sign of pneumoperitoneum. Br J Radiol 69(824):774-776, 1996 9. Shogilev DJ, Shapiro NI: Diagnosing appendicitis: Evidence-based review of the diagnostic approach. West J Emerg Med 15:859-871, 2014 10. Karul M, Berliner C, Keller S, et al: Imaging of appendicitis in adults. Rofo 186:551-558, 2014 11. Deshmukh S, Verde F, Johnson PT, et al: Anatomical variants and pathologies of the vermix. Emerg Radiol 21:543-552, 2014 12. Wakeley CP: The position of the vermiform appendix as ascertained by an analysis of 10000 cases. J Anat 67:277-283, 1993 13. Humes DJ, Simpson J: Acute appendicitis. Br Med J 333:530-534, 2006 14. Chin CM, Lim KL: Appendicitis: Atypical and challenging CT appearances. Radiographics 1:123-124, 2015 15. Barlow A, Muhleman M, Gielecki J, et al: The vermiform appendix: A review. Clin Anat 26:833-842, 2013 16. Gaetke-Udager K, Maturen KE, Hammer SG: Beyond acute appendicitis: Imaging and pathologic spectrum of appendiceal pathology. Emerg Radiol 21:535-542, 2014 17. Jacobs JE, Balthazar EJ: Diseases of the appendix. In: Gore RM, Levine MS (eds): Textbook of Gastrointestinal Radiology. Philadelphia, PA: Saunders; 1030-1069, 2007 18. Daniele S, Nicotra S, Liguori C: Acute perforated appendicitis: spectrum of MDCT findings. In: Romano L, Pinto A (eds): Imaging of Alimentary Tract Perforation. Springer 45-51, 2015 19. Athanasios NC, ioanna T, et al: CT in appendicitis. Diagn Interv Radiol 13:19-25, 2008 20. Kontopodis N, Kouraki A, Panagiotakis G, et al: Efficacy of preoperative computed tomography imaging to reduce negative appendectomies in patients undergoing surgery for left lower quadrant abdominal pain. G Chir 35:223-228, 2014 21. Pickhardt PJ, Lawrence EM, Pooler BD, et al: Diagnostic performance of multidetector computed tomography for suspected acute appendicitis. Ann Intern Med 154:789-796, 2011 22. Bixby SD, Lucey BC, Soto JA, et al: Perforated versus nonperforated acute appendicitis: Accuracy of multidetector CT detection. Radiology 241: 780-786, 2006
36 23. Pooler BD, Lawrence EM, Pickhardt PJ: Alternative diagnoses to suspected appendicitis at CT. Radiology 265:733-742, 2012 24. Maniatis V, Chryssikopoulos H, Roussakis A, et al: Perforation of the alimentary tract: Evaluation with computed tomography. Abdom Imaging 25:373-379, 2000 25. Stoker J, van Randen A, Laméris W, et al: Imaging patients with acute abdominal pain. Radiology 253:31-46, 2009 26. Kanona H, Al Samaraee A, Nice C, et al: Stump appendicitis: A review. Int J Surg 10:425-428, 2012 27. Ramdass MJ, Young Sing Q, Milne D, et al: Association between the appendix and the fecalith in adults. Can J Surg 58:10-14, 2015 28. Rao PM, Wittenberg J, McDowell RK, et al: Appendicitis: Use of arrowhead sign for diagnosis at CT. Radiology 202:363-366, 1997
F. Iacobellis et al. 29. Weltman DI, Yu J, Krumenacker Jr J, et al: Diagnosis of acute appendicitis: Comparison of 5 and 10 mm CT sections in the same patient. Radiology 216:172-177, 2000 30. Fraser JD, Aguayo P, Sharp SW, et al: Accuracy of computed tomography in predicting appendiceal perforation. J Pediatr Surg 45:231-234, 2010 31. Pickhardt PJ, Levy AD, Rohrmann Jr CA, et al: Primary neoplasms of the appendix manifesting as acute appendicitis: CT findings with pathologic comparison. Radiology 224:775-781, 2002 32. Pooler BD, Lawrence EM, Pickhardt PJ: MDCT for suspected appendicitis in the elderly: Diagnostic performance and patient outcome. Emerg Radiol 19:27-33, 2012 33. Novelline RA, Rhea JT, et al: Helical CT in emergency radiology. Radiology 213:321-339, 1999
Introduction
A
limentary tract perforations constitute an emergency condition requiring prompt diagnosis and surgical treatment.1,2 The diagnosis depends on clinical suspicion and especially on imaging tests that permit defining the presence, the level and cause of perforation.3-8 Appendicitis is the most common cause of acute abdomen and the most common acute condition requiring surgery.9,10 The vermiform appendix, usually located to the right side at the apex of the cecum, at the junction of the 3 taeniae coli, can be considered as a true diverticulum of the cecum as it has all of the layers of the colonic wall: mucosa, submucosa, muscularis (longitudinal and circular), and the serous. The appendix may be detected in a various range of positions on imaging examinations owing to its variable course. Retrocecal is the most common (Fig. 1); alternative routes are retroileal, preileal, pelvic, cross midline, and also into the hepatorenal recess.11-13 Left-sided appendicitis may be rarely found in patients with congenital intestinal malrotation and situs inversus.14 The appendix may have a variable length, ranging from 5-35 cm and average of *Department of Diagnostic Imaging, Pineta Grande Medical Center, Castel Volturno, Italy. †Department of Radiology, Second University of Naples, Naples, Italy. ‡Department of Radiology, Darent Valley Hospital, Dartford & Gravesham NHS Trust, Dartford, UK. Address reprint requests to Francesca Iacobellis, MD, via Domitiana Km 30.000, 81030 Castel Volturno CE, Italy. E-mail: [email protected]
http://dx.doi.org/10.1053/j.sult.2015.10.002 0887-2171/& 2016 Elsevier Inc. All rights reserved.
9 cm.11,15 The risk of developing acute inflammation of the appendix in the lifetime is approximately 7%,10 mostly involving patients from 10-30 years16; there is a slight predilection for male gender.17 Mortality and morbidity rates related to surgical intervention for appendicitis are 0.24% and 6.1%, respectively, and 1.7% and 19% for perforated appendicitis.17 Signs and symptoms may depend on the inflammatory stage of the appendicitis and on the anatomical location of the appendix.11,18 Usually the clinical presentation is characterized by abdominal pain in the right inferior quadrant, nausea, vomiting, fever, anorexia, and laboratory leucocytosis.19 The pathophysiology of acute inflammation largely depends on luminal obstruction; other contributing processes are viral infections, poor diet, ischemia, and trauma.16,18 Luminal obstruction may be due to appendicolith (450% of cases) (Fig. 2), lymphoid hyperplasia of the appendix wall, foreign bodies, parasites, neoplasia, and metastasis.18 Following the obstruction, there is a lumen distension with an increase of endoluminal pressure and, in less vascularized wall area, this is responsible for a further reduction in the arterial blood flow, leading to perforation due to ischemic necrosis of the wall.18 In 80% of cases, the typical clinical picture and the laboratory data lead to the correct diagnosis, and in approximately 20% of cases the findings can be atypical and subtle, with a large variety of sign and symptoms, and the differential diagnosis may be challenging, especially in young female patients and in the elderly people.18 31
F. Iacobellis et al.
32
A
C
B
Figure 1 Appendicitis. MDCT axial scans (A) and (B) and coronal MPR image (C) show a distended, thickened wall (11 mm) inflamed appendix, with a slightly increased wall enhancement and stratification (arrow). There is stranding of the adjacent perivisceral fat with multiple lymphoadenopathies and a fluid around the appendix (arrowhead). Free fluid in the right parietocolic recess is also seen (asterisk in C). MPR, multiplanar reconstructions.
Imaging plays a crucial role when the clinical presentation is atypical and differential diagnosis mimicking appendicitis needs to be excluded.20 The available imaging modalities include ultrasound (US), multidetector computed tomography (MDCT), and magnetic resonance imaging. US is the first imaging test, particularly in patients with mild abdominal pain and women. Abdominal CT with intravenous contrast medium (IVCM) is now considered the standard of care.16,21 It is firstly required in patients with acute abdomen and atypical clinical presentation of appendicitis and suspected perforation.10,22 Owing to the high sensitivity (87%-99%) and specificity (92%-99%), it is the imaging modality of choice for an accurate diagnosis and to reduce unnecessary laparotomies.9,18,20 Furthermore, in adult patients clinically suspected for an appendicitis, CT may identify an alternative cause for symptoms, which often requires hospitalization and surgery for treatment.23 Magnetic resonance examination, if available in emergency setting, is the first choice in pregnant women.10 This review is particularly focused on the MDCT assessment of perforated appendicitis.
A
MDCT Imaging MDCT is considered the most valuable imaging technique in the identification of presence, site, and cause of alimentary tract perforations and some authors consider CT as the primary technique for the diagnosis of acute abdominal pain.2–8,24,25 Prompt diagnosis of perforated appendicitis is important considering the surgical implications and complications.
Study Protocol In the era of MDCT, all the examinations have to be performed with a high-resolution protocol, with slice thickness and a reconstruction interval values of approximately 1 mm, completed by multiplanar reconstructions. In our institution all examinations are acquired by a 128 slices dual-source CT system (Siemens Somatom Definition Flash), with slice thickness of 1.2 mm, collimation of 2 128 0.6 mm3, and rotation time of 0.28 seconds. The protocol includes IVCM administration with scans acquisition from the dome of the diaphragm to the symphysis pubis. Enteric contrast agent is
B
Figure 2 Perforated appendicitis. Sagittal MPR image (A) and MDCT axial scan (B) show a tortuous, fluid-dilated appendix with increased wall enhancement (arrow). Note also some endoluminal appendicolithes and air gas bubbles. Free fluid is seen around the cecum (asterisk in A). MPR, multiplanar reconstructions.
CT of perforated appendicitis
A
33
B
C
Figure 3 Perforated appendicitis. MDCT axial scan (A) and coronal MPR images (B and C) show inflamed appendix (arrow), distended by fluid with parietal hyperenhancement and an appendicolith within the lumen. A parietal defect can be appreciated in the distal part, where an extraluminal air loculus is also seen (C). A large fluid collection in the right iliac fossa is also visible (arrowhead). MPR, multiplanar reconstructions.
not administered. The IVCM, 80-100 mL of iodinated contrast agent at 400 mg/mL concentration injected at 3-4 mL/s followed by 50 mL of saline injected at the same flow-rate, is necessary to enhance the bowel walls and solid organs. An automated bolus tracking, with region of interest placed in the descending aorta at an attenuation threshold of 100 HU, may be used to time the beginning of the arterial phase, if retained depending on the clinical suspicion. The study of the bowel wall is optimal in the portal phase (70-second delay from the end of injection). To identify and to display the appendix in its length, 3-dimensional multiplanar reconstruction are useful.
CT Findings When approaching the abdominal CT of patients with acute abdomen from suspected appendicitis it is important to
A
B
correctly identify the cecum and it should not be assumed that the appendix is normal if it is not seen in the right lower quadrant, as some congenital anomalies are related with leftsided appendix.14 The position of the base of the appendix is relatively constant, between the ileocecal valve and the apex of the cecum, and this relationship is maintained even when the cecum is mobile. The location of the tip of the appendix may be more variable, as described earlier, and it is important to explore the appendix in its whole length as it is possible to develop inflammation confined to the distal portion of the appendix, a condition known as “tip appendicitis.”16 The cecum has to be examined even if in the clinical history of the patients a previous appendectomy is reported, as it is possible to develop inflammation of even the residual appendix after a prior incomplete appendectomy. This is known as “stump” appendicitis.16,26 In normal condition the maximum diameter of the appendix (wall to wall) is 0.6 cm with a wall thickness of approximately 0.1 cm, the lumen may contain fluid or gas, and the
C
Figure 4 Perforated appendicitis. MDCT axial scan (A) and coronal MPR images (B and C) show hyperenhancement of the appendiceal wall, thickened and distended by fluid that appears located caudally to the cecum (arrow). A hyperdense appendicolith is seen in the lumen (C) as well as multiple millimetric air loculi (B); furthermore, enhancing defect foci of the wall are seen. There is stranding of the periappendicular mesenteric fat with free fluid surrounding the appendix (arrowhead). MPR, multiplanar reconstructions.
F. Iacobellis et al.
34 surrounding mesenteric fat tissue appears homogeneous. Appendicoliths may be seen in a noninflamed appendix too.27 Main signs of appendix inflammation include: – – – – – – –
enlarged lumen, wall thickening, alterations of the parietal enhancement, “arrowhead” sign, surrounding fat alteration, abscess formation, and inflammation of adjacent organs.10,18
Owing to the appendiceal obstruction and to the mucosal continuous secretion, the lumen of the inflamed appendix become enlarged with a wall-to-wall caliber wider than 0.6 cm (Figs. 1, 2, and 4). In the early stages of the inflammation there is an increase in the blood supply with wall hyperemia (hyperenhancement) and thickening of the wall of the appendix that becomes more than 0.2 mm (Figs. 1-4). The “arrowhead” sign is a focal symmetric thickening of the cecal wall near the appendiceal base that may be seen when oral or rectal (or both) intraluminal contrast is administered. It has a low sensitivity (30%) but high specificity (100%).28 In response to the inflammatory reaction, the adipose tissue surrounding the appendix increases in density and appears as “dirty fat” sign29 (Figs. 1 and 4). If there is a progression in the pathology, and the lumen becomes overdistended, it causes an impairment in the blood supply to the wall with the evidence of reduced vascularization area and ischemic parietal zone formation (hypoattenuating after IVCM) (Figs. 3 and 4). This process leads to perforation of the appendix, which is a condition requiring surgery (Figs. 1-5). The periappendicular reaction increases (Fig. 1) and the leak of enteric material causes the development of a local phlegmon, without a clear wall, usually detected at the apex of the appendix. When the phlegmon acquires a definite thick wall, showing peripheral enhancement after IVCM administration, it is a clear sign of progression into abscess (Fig. 5).
A
B
In more advanced cases, an involvement of contiguous tissues and organs in the inflammatory-infectious process may be seen, with free fluid detection in the peritoneum related to the inflammatory response18 (Figs. 1, 2, and 4). Based on anatomopathologic findings, appendicitis can be classified as follows: – catharral appendicitis when inflammation is limited to the mucosal layer, – phlegmonous appendicitis when the wall is more involved in the inflammatory process with the progressive development of intraparietal microscopic phlegmon presence, and – gangrenous appendicitis when there is an extensive necrosis of the wall. Perforation of the appendix is not easy to detect; a study evaluating CT sensitivity for perforation in the pediatric population found it to be approximately 62%.30 Especially at the beginning of the process the signs are subtle; otherwise, when the perforation has been present for some time, the phlegmon or abscess might completely obscure the perforated appendix.16 However, the diagnosis of perforated appendix is crucial as perforation increases the risk complication after surgery. The most specific signs related to perforated appendix are the following. – Abscess presence is considered to be the most specific sign of perforation and it represents the most frequent complication of perforated appendicitis. – Detection of foci defects in the wall has a high sensitivity of 95%, a specificity of 97%, and an accuracy of 96%. – Phlegmon presence has reported specificity of 95% but low sensitivity (40%). – Extraluminal air appears as the presence of bubble gas outside the appendix. This sign is highly (98%) specific but has low sensitivity of 22%-35%. – Finding of extraluminal appendicolith is also highly (100%) specific, but poorly (32%) sensitive.18 The
C
Figure 5 Perforated appendicitis. MDCT MPR in coronal (A), axial (B), and sagittal (C) planes show a retrocecal thickened perforated appendix (A: arrow) with a contiguous air-fluid collection (A-C: arrowhead) in which a hyperdense appendicolith (A-C: curved arrow) is seen. There is stranding of the periappendicular mesenteric fat with multiple lymphoadenopathies (B: circle). MPR, multiplanar reconstructions.
CT of perforated appendicitis presence of appendicolith may accelerate the occurrence of perforation.14 The most frequent complications of perforated appendix are represented by abscess formation and peritonitis. The development of peritonitis secondary to perforation is more frequent in children due to rapid progression from inflammation to wall rupture. In adults, the inflammatory adhesions developing around the site of inflammation try to arginate the inflammatory process, leading more frequently to phlegmons and abscesses formation instead of a rapid evolution in peritonitis.14 Other complications that may be detected in the abdominal cavity following appendix perforation are pylephlebitis and pylethrombosis related to ascending infection along the mesenteric portal venous system; ureteral reactive involvement with different grades of hydroureteronefrosis; gangrenous appendicitis; dynamic or mechanical bowel obstruction due to the bowel reaction to the inflammation or to the narrowing of the terminal ileum in relationship with periappendicular inflammatory reaction; and fistula with other contiguous organs such as bladder, vagina, uterus, and skin.14
Differential Diagnosis In acute settings, it is important to differentiate other entities from appendicitis because some of the other conditions can be managed conservatively.12 The most frequent pathologic conditions that must be differentiated from the appendicitis are: – pathologies starting from the appendix such as appendiceal diverticulitis, appendiceal mucocele (due to chronic obstruction in absence of acute inflammation or due to benign or malignant neoplasms); and primary neoplasms of the appendix31,32; – pathologies with secondary involvement of the appendix such as enterocolitis, cecal diverticulitis, and Crohn's disease; and – pathologies that mimic appendicitis such as bowel obstruction, intussusceptions, acute cholecystitis, perforated duodenal ulcer, Meckel's diverticulitis, colonic diverticulitis, pancreatitis, right renal colic or pyelonephritis, epiploic appendagitis, mesenteric adenitis, and gynecologic processes such as functional ovarian cyst bleeding, ovarian torsion, salpingitis or pelvic inflammatory disease, ectopic pregnancy, pyosalpinx, tuboovarian abscess, and endometriosis.18,33
Conclusion Acute appendicitis is a frequent pathology that is clinically diagnosed usually, but in some cases the diagnosis may be challenging. MDCT, owing to its high sensitivity and specificity, is the imaging modality of choice to make an accurate diagnosis among the different surgical conditions that need to be differentiated from acute appendicitis, to avoid the
35 complications related to the perforation, detecting the early signs of inflammation, or to identify the sign of perforation suggesting a prompt surgical intervention. MDCT can also reduce unnecessary laparotomies, allowing to correctly manage patients with medical condition mimicking acute appendicitis.
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