Ultrasound Imaging of Appendicitis

Abstract

Ultrasound is a handy tool in diagnosing appendicitis and its possible complications. The sensitivity and specificity of ultrasound in diagnosing appendicitis can be comparable to CT and MRI owing to a highly skilled and experienced operator, high-quality equipment, and slim patients. A multi-imaging approach is advisable when ultrasound findings are inconclusive, that is, when you do not visualise the normal appendix in patients with a high clinical suspicion of appendicitis. During the ultrasound evaluation of appendicitis, it is essential to initially examine the organs of the abdomen and pelvis to rule out other mimicking pathologies before switching to a high-frequency transducer to examine the bowel and appendix. The normal appendix on ultrasound appears blind-ending, tubular, compressible, and non-peristaltic, adjacent to the caecum and terminal ileum, usually in the right iliac fossa. Adopting various ultrasound scanning techniques, including ‘mowing the lawn,’ ‘graded compression,’ and a combination of supine and lateral decubitus scanning positions, helps to improve the visualisation of the appendix and the diagnosis of appendicitis. It is imperative to differentiate between uncomplicated and complicated appendicitis by evaluating their ultrasound features. However, in some cases, there is limited imaging accuracy in making this differentiation.

1. Introduction

Appendicitis is the inflammation of the vermiform appendix [1]. An appropriate diagnosis remains challenging for many clinicians and imaging specialists despite being a well-known disease and a common reason for emergency operation (appendectomy) [1]. The overall clinical aim to keep the rate of negative appendectomies to the possible minimum necessitates the correct preoperative imaging diagnosis of appendicitis [2, 3]. For instance, one study [4] found a link between patients who had appendectomy and tonsillectomy in childhood having a higher risk of developing myocardial infarction later in life. While the relationship has not yet been well-established in the literature [4], this, in conjunction with surgical risks, further highlights the importance of a limited negative appendectomy rate in practice, thereby increasing the requirement of an accurate diagnosis of appendicitis clinically and on imaging.

The gold standard in the imaging of appendicitis is Computed Tomography (CT), with a sensitivity and specificity of 81–94% and 90–94%, respectively, and readily available to many emergency departments in the western world [5]. Furthermore, Magnetic Resonance Imaging (MRI), with a sensitivity and specificity of 96%, respectively, is very useful in diagnosing appendicitis, particularly in pregnant women [5]. However, there is a growing interest in using Ultrasound (US) as the first line of appendicitis imaging, with a conditional CT scan when US findings are equivocal [5, 6, 7].

Unlike CT and MRI, US has a varying but lower sensitivity of 35% - 90% and a specificity of up to 90%; however, it uses high-frequency sound waves, which are primarily known to remain harmless within diagnostic frequencies [8]. On the other hand, CT uses ionising radiation that poses some risks, particularly to children and women of childbearing age, and is potentially more expensive than US [8]. For instance, one study [9] revealed the presence of a link between patients with cancer and previous exposure to CT radiation, with CT abdomen and pelvis being one of the culprits; therefore highlighting the importance of avoiding unnecessary radiation to our patients and reinforcing the need for US as the first line of imaging in appendicitis. MRI, though relatively safe, is not cheap and may sometimes require sedation in children to keep still for the examination, which is not always practical in real-life situations [10]. MRI also has less accessibility when compared to US [10]. However, there are some drawbacks with ultrasound in examining for appendicitis which include; difficulty in scanning patients with high BMI, a high degree of transducer tenderness leading to limited visualisation of the structures, and the most significant limitation is that US is highly operator dependent, hence the variability in its sensitivity [11]. Some main factors that improve the diagnostic accuracy of US in appendicitis include; a highly skilled operator, good quality ultrasound equipment, and patient characteristics.

This chapter aims to provide some information on the ultrasound anatomy and appearances of the normal appendix, uncomplicated appendicitis, and complicated appendicitis, i.e., gangrenous and perforated appendicitis, and to provide some information on how to acquire the US images, and how to recognise different US patterns encountered in practice. These are achieved by extracting useful information from a combination of the current and relevant literature on this topic, a reflection on the author’s many years of experience in carrying out ultrasound examinations of appendicitis, and the knowledge obtained from numerous training sessions delivered by other experts from across the globe.

2. Training and quality control

Globally, US evaluation of appendicitis is generally performed daily across diverse professional specialties in the hospital, ranging from sonographers, radiologists, emergency physicians, gastroenterologists, and general practitioners. Therefore, this chapter will collectively refer to these as ‘the ultrasound examiner.’

The need for appropriate training in the area cannot be overemphasised for an accurate understanding of the various imaging appearances of an inflamed appendix and a correct diagnosis of appendicitis. In addition, it is imperative to understand the basic anatomy of the appendix, its usual location, orientation, and relationship to the neighbouring bowel anatomically and pathologically. The latter will be discussed later in this chapter. Also, it is advisable to follow up on the outcomes of cases examined and to welcome feedback from referring clinicians and surgeons, which helps with better development.

Furthermore, understanding the US machine’s knobology, transducer selection, and fundamental ultrasound physics, among others, will help the ultrasound examiner with the safe and efficient usage of the US equipment to maximise its diagnostic potential. Although details of the latter are beyond the scope of this chapter, the next section will provide some relevant information regarding the US equipment.

3. Equipment

There are different kinds of US machines ranging from whole units to portables; tabletop and handheld machines with wireless display connectivity to regular mobile devices and tablets for ease of use within the hospital and community setting [12]. An appropriate US examination in the evaluation of appendicitis requires a combination of a curved-array transducer with a frequency range of 1–6.5 MHz (C1–6), a ‘medium range’ high-frequency linear-array transducer of 9 MHz (9 L), and occasionally, a higher frequency linear-array transducer of up to 15 MHz (15 L) for examining the appendix in younger children, and very slim adults [13]. However, in practice, the 9 L transducer is usually sufficient in evaluating the appendix in most patients after using the C1–6 in examining the other abdomen and pelvic organs for pathologies that might mimic appendicitis; like cholelithiasis, gynaecological and renal pathologies.

4. Ultrasound terminologies and scanning techniques

4.1 Terminologies and pattern recognition

For clarity to those new to ultrasound; the primary term used to describe structures/patterns displayed on US imaging is called ‘echogenicity’ or ‘echotexture,’ which is based on the level of interaction between the ultrasound beams and the individual tissue, i.e., anatomical or pathological structure seen within the region being insonated. For instance, because clear fluid allows a ‘through transmission’ of the ultrasound beam, this is therefore represented on the display monitor as ‘anechogenic’ or ‘anechoic’ with an increased posterior acoustic enhancement. On the other hand, structures with a high calcium content, e.g., bones and other calcifications like appendicoliths, reflect most of the ultrasound beam to the transducer, therefore appearing ‘hyperechogenic’ or ‘hyperechoic’ with posterior acoustic shadowing. Other structures between the spectrum mentioned above, like pus, masses, and purulent appendiceal contents, are sometimes described as ‘hypoechoic’ with reference to the surrounding anatomical structures, depending on their content.

4.2 Doppler ultrasound

Doppler Imaging, i.e., Colour (CD) and Power Doppler (PD), are mandatory functions used during US examination of appendicitis to check for evidence of vascularity which has been directly linked to inflammatory activities evident mostly in uncomplicated appendicitis [14]. While CD function is usually sufficient on most newer US equipment to interrogate for vascularity within and around the inflamed appendix, PD is also sometimes beneficial in evaluating traces of vascularity with limited detectability on CD [14]. The application of these functionalities and the adoption of appropriate scanning techniques will improve and maximise the diagnostic efficacy of ultrasound in appendicitis. The ultrasound examiner must optimise the US machine’s CD setting during the evaluation of appendicitis; this is done by ensuring that the Pulse Repetition Frequency (PRF) or ‘scale’ is adjusted to help detect slow blood flow velocities within the region [15]. If the PRF is set too high, ‘aliasing’ may occur, leading to a false negative diagnosis of hypervascularity [15]. Furthermore, most US machines have other functions like Microvascular Imaging (MI) or superb microvascular imaging (SMI) and B Flow Imaging (B Flow) that are designed to have more sensitivity than CD [16, 17]. However, their nomenclatures may vary across manufacturers.

4.3 Scanning technique

The common symptoms of appendicitis include the acute onset of periumbilical or central abdominal pain, eventually radiating to the right iliac fossa (RIF) [18]. This abdominal pain can sometimes be vague, particularly in children, and can mimic symptoms of some other abdominal or gynaecological pathologies [18]. Therefore, it is highly recommended that an ultrasound examination of appendicitis should initially include; the entire abdomen and pelvis to rule out pathologies that might mimic appendicitis, and the rest of the bowel, before becoming more focused on the appendix in the RIF [19]. The patient is initially examined in a supine position, then asked to turn to the left lateral decubitus position to aid a better visualisation of the appendix.

4.3.1 Mowing the lawn

A curvilinear transducer with a frequency range of 2–6.5 MHz should be initially used in examining the abdomen and pelvic organs to rule out common pathologies like cholelithiasis, nephrolithiasis, possible signs of pyelonephritis, ovarian cysts, among others. Furthermore, using the same transducer, the examiner should continue by imaging the bowel from the LIF in the region of the sigmoid colon (usually in a fixed location) in a ‘lawn-mowing’ fashion to the RIF to rule out some bowel pathologies like inflammatory bowel diseases (IBD), diverticulitis, ileocecitis, and the like [19]. During the examination, a gentle and slow movement of the high-frequency transducer in a vertical sweeping direction across the abdomen helps examine most parts of the small and large bowel [19].

4.3.2 Graded compression

Subsequently, the examiner should switch to a 9 MHz linear transducer to reexamine the bowel again (as described in Section 5.3.1.); slowly from the LIF to the RIF with the final focus on the site of the patient’s pain (expectedly the RIF) while applying graded compression on the abdomen throughout the examination. Graded compression, first described in 1986 by JB Puyleart [20], is an essential aspect of ultrasound imaging in appendicitis. It is described as the use of the (linear) transducer to apply gentle and gradual yet firm pressure on the abdomen to displace the bowel gas and luminal content, bringing the examined bowel structure (and pathology) closer to the view of the ultrasound transducer and the examiner [20].

4.4 Other ultrasound techniques

A transvaginal examination can be offered to some female patients when the inflamed appendix extends into the right hemipelvis or when there is a gynaecological pathology that is not well visualised on the transabdominal US imaging [21]. However, adequate prior training and competence are advised before undergoing such an intimate examination.

There is a growing increase in the roles of newer ultrasound techniques like contrast-enhanced ultrasound (CEUS) and elastography in diagnosing appendicitis. However, these are not yet well established across literature and require conventional ultrasound expertise to be performed correctly, and also not routinely used in the diagnostic workup and classification of appendicitis [22, 23, 24]. Ultimately, it is crucial to work in line with the hospital/imaging department’s protocols and to work based on individual patients’ requirements while respecting the patient’s dignity and privacy throughout the examination.

5. Ultrasound anatomy

The normal appendix measures between 2 cm - 10 cm in length and ≤ 0.6 cm in anteroposterior (AP) dimension, having its base attached to the inferior surface of the caecum in the RIF, and its body and fundal tip in varying orientation, depending on; the location of the caecum, the length of the appendix, and its orientation of attachment to the caecum [25]. The appendix is predominantly antecaecal in orientation; however, some are retrocaecal, pelvic, and in rare cases, subhepatic, with the base usually only a few centimetres distal to the ileocaecal junction [25, 26]. On US, the normal appendix (Figure 1) appears as a blind-ending, tubular, compressible, and non-peristaltic loop of bowel with its base adjoining the distal end of the caecum and in a slightly inferior position to the terminal ileum and ileocaecal junction [25, 26]. It is also commonly inferior-medial to the right psoas muscle and the right external iliac vessels (Figures 1 and 2). In rare cases, the appendix can be seen extending into the right hemipelvis or slightly higher in an ascending fashion towards the subhepatic region [25, 26].

Figure 1.

Sonograms of the normal appendix from the same patient. A: The normal appendix (between arrows) in a transverse orientation; note the ‘target’ appearance and the longitudinal segment of the terminal ileum (TI) coursing anterior to the appendix (arrow heads), and the iliac artery (star). b: The longitudinal segment of the appendix in a longitudinal orientation, with no appreciable flow seen on colour Doppler; also note the terminal ileum in an oblique orientation anterior to the appendix and the psoas posteriorly.

Figure 2.

Sonogram of the normal appendix in a longitudinal orientation showing its individual wall layers (numbered 1–5), with the obliquely imaged terminal ileum (between arrows) anterior to the appendix and the psoas (star) muscle.

Like the rest of the bowel, on ultrasound, the normal appendix; usually with barely any flow evidence on CD (Figure 1b), has five concentric layers [27] of hyper-hypoechogenicity (see Figure 2), namely:

1. Hyperechoic serosa (outermost layer)

2. Hypoechoic muscularis propria

3. Hyperechoic submucosa

4. Hypoechoic mucosa

5. Hyperechoic mucosal interface (innermost/luminal layer)

However, routinely on ultrasound, only three of these five layers are easily visualised in a normal appendix: the mucosa, mucosal interface, and submucosa, with the latter being the most apparent echogenic layer [27]. In practice, care must be taken by the ultrasound examiner when measuring the appendix not to confuse the submucosal layer for the outermost serosa, as this is a habitual error made by beginners which can lead to an under-measurement of the appendix and consequently a false negative diagnosis, further delaying patient’s management. Owing to this, always measure the appendix (Figure 3a) from serosa to serosa (S2S) to cover its maximum outer diameter (MOD). Therefore, visualising and identifying the individual layer of the appendix is essential in the proper diagnosis of (uncomplicated) appendicitis on ultrasound [28].

Figure 3.

Uncomplicated appendicitis sonograms acquired from different patients. A: Shows the inflamed appendix (between callipers) measuring 10 mm (MOD) from serosa to serosa (S2S), also note the echogenic periappendiceal mesenteric fat wrapping/mesenteric oedema (stars) around the inflamed appendix. b: Shows an inflamed appendix (APP., arrow) in a longitudinal orientation with mild periappendiceal mesenteric oedema (stars) and normal terminal ileum (TI, arrow heads) seen coursing anterior to the appendix from the distal ileum towards the caecum in the RIF (not imaged).

6. Uncomplicated appendicitis

6.1 Overview

Uncomplicated appendicitis is the inflammation of the appendix without any further complications [29]. It is now believed that uncomplicated and complicated appendicitis are of two separate entities and etiologies; therefore, one does not lead to the other [30]. Although details of the causes and treatment options of uncomplicated and complicated appendicitis are beyond the scope of this chapter, features seen on ultrasound to help in the correct diagnosis of uncomplicated appendicitis are discussed in the subsections below.

6.2 Ultrasound features

An inflamed appendix on ultrasound appears as a blind-ending, tubular, non-compressible, and non-peristaltic bowel structure, usually in the RIF measuring >0.6 cm in AP dimension from S2S [31].

The primary ultrasound features of uncomplicated appendicitis [31, 32] include (Figure 3);

• Visualisation of an inflamed non-compressible appendix measuring above 0.6 cm,

• Increased echogenicity of the periappendiceal mesentery (i.e., mesenteric oedema) and

• The visualised appendix corresponding to the site of the patient’s maximum transducer tenderness.

In addition, the secondary ultrasound features [28, 33] of uncomplicated appendicitis are;

• Mesenteric lymphadenopathy,

• Increased appendiceal wall vascularity (Figure 4),

• Moderate amount of free fluid in the RIF, and

• Free fluid in other regions of the abdomen and pelvis.

Figure 4.

Sonograms acquired from different patients showing hypervascularity in uncomplicated appendicitis. A: Shows an inflamed appendix in a longitudinal orientation with significantly increased vascularity affecting roughly all the layers of the appendix; note the low PRF setting on the colour scale to the left of the image. b: Shows a transverse cross-section of the fundus of a focally inflamed appendix; note that the increased vascularity seen affects only the submucosa layer of the wall of the appendix (same patient as in Figure 5).

To further emphasise; in order to rule out appendicitis on ultrasound, the normal appendix (see Section 6) must be visualised [34]. In the absence of the latter, the ultrasound report should generally be along the lines of ‘the appendix has not been visualised; however, no secondary ultrasound features of appendicitis seen.’ Owing to the expectation that the examination was correctly done using the proper scanning techniques, equipment, and that the US examiner has accomplished appropriate US training (explained in the previous sections).

6.3 Hypervascularity

Ultrasound reveals hypervascularity of an inflamed appendix as the increase in colour Doppler flow (CDF) signal within the wall of the appendix (Figure 4); most commonly the echogenic submucosa layer (Figure 3b), which is also the most prominent layer seen on US in uncomplicated appendicitis [35]. Usually, the presence of CDF within the walls of an inflamed appendix without any features of complications (Section 9) confirms the diagnosis of uncomplicated appendicitis and potentially rules out a gangrenous appendix [35].

6.4 Focal appendicitis

Focal appendicitis occurs when only a region of the appendix is inflamed (Figure 5), affecting mainly the appendix base or fundal region; this can lead to a false negative ultrasound diagnosis if the appendix has not been examined in its entirety [33, 36]. This highlights the importance of visualising all parts of the appendix during an US examination. Therefore, it is mandatory to state in the ultrasound report the study limitations encountered if a complete diagnosis was not attained, availing the patient of prompt diagnosis by another ultrasound examiner or other imaging modalities.

Figure 5.

Sonograms obtained from the same patient showing focal appendicitis that mainly affected the fundal region of the appendix. A: Shows the appendix with callipers measuring varying sections from S2S; the base measured 0.4 cm, the body 0.7 cm, and the fundal tip measured 1.0 cm in AP calibres. b: Shows the blind end of the focally inflamed appendix (between arrows) with no significant periappendiceal mesenteric oedema.

6.5 Atypical uncomplicated appendicitis

Some atypical cases of appendicitis occasionally diagnosed on ultrasound include; long (or high) ascending retrocecal appendicitis (LARA), pelvic appendicitis (PA) using the transabdominal and possibly transvaginal approach, and appendicitis during pregnancy (ADP).

6.5.1 Appendicitis during pregnancy (ADP)

The sensitivity of US in the detection of ADP is known to be low, and it further declines as the pregnancy progresses; for instance, one study [37] found a sensitivity of 69%, 63%, and 51% in the first, second, and third trimesters respectively. Their respective specificity was 85%, 85%, and 65% [37]. During pregnancy, the appendix and the rest of the bowel ‘give way’ to the growing gravid uterus; therefore, personnel experience plays a crucial role in visualising the appendix with ultrasound in these patients, as the appendix will tend to be located higher or in a more lateral position than in a non-pregnant patient [37, 38]. Owing to this, MRI, with much higher sensitivity and specificity than US, is considered the imaging modality of choice in this case if ultrasound is inconclusive or unavailable [38].

6.5.2 Pelvic appendicitis (PA)

PA occurs when an inflamed appendix extends into the pelvis (majorly the right hemipelvis), with an US appearance of a blind-ending, tubular, non-peristaltic bowel loop medial (Figure 6a) or lateral (Figure 6b) to the right ovary measuring >0.6 cm with evidence of hypervascularity (Figure 6c), which in some cases will present with increased adjacent bowel wall thickening secondary to the inflamed appendix (Figure 6a) [21]. The inflamed appendix usually corresponds to the site of the patient’s maximum tenderness and elicits a pain response when in contact with the ultrasound transducer [21].

Figure 6.

Pelvic appendicitis. A: A transvaginal sonogram of the right hemipelvis showing the right ovary (star), an inflamed appendix (arrows), and a slightly thick-walled adjacent bowel loop (arrow heads) secondary to the inflamed appendix. b: A transabdominal sonogram of the right hemipelvis obtained using a 9 MHz linear transducer with the appendix (arrow) and some echogenic periappendiceal mesenteric oedema (stars), and the normal right ovary medial to it. c: Shows hypervascularity on colour Doppler of the inflamed appendix of the same patient in a.

6.5.3 Long ascending retrocecal appendicitis (LARA)

In the case of LARA, the inflamed appendix courses craniomedial to the psoas muscle (Figure 7) from its basal connection to the caecum in the RIF towards the subhepatic region (Video 1, https://youtu.be/BhE1OIzoKLI), and due to its location, patients with LARA can present with symptoms mimicking other abdominal pathologies like biliary or urinary pathologies [39]. Therefore, a thorough examination of the other abdominal organs and a careful identification of the other bowel structures like the terminal ileum and caecum can help the ultrasound examiner to locate the appendix in this case.

Figure 7.

Long ascending retrocecal appendix. (a) Reveals a sonogram acquired with the patient in a left lateral decubitus position, showing a long retrocecal appendix (arrow) coursing medial to the psoas muscle (posterior surface) and extending towards the right subhepatic region. The appendix was focally inflamed at the base, as seen in (b), where it measured 0.7 cm (between callipers), while the rest of the appendix appeared normal. Video 1 (https://youtu.be/BhE1OIzoKLI) shows the long ascending retrocecal appendix in transverse orientation with some reactive lymph nodes seen adjacent.

7. Appendicoliths

Appendicoliths are calcified structures seen within the lumen of the appendix [40]. They are formed from an aggregation of faecal materials that calcifies over time and are usually made up of calcium phosphatase with some faecal and organic matter [40]. Known as a common culprit in the occlusion of the appendiceal lumen leading to appendicitis, however, appendicoliths have been found in many patients without appendicitis [41]. On US, appendicoliths appear as an echogenic (calcific) structure seen within the lumen of the appendix and usually present with posterior acoustic shadowing caused by a near-complete reflection of the US beam on it (Figure 8) [42]. The presence of an appendicolith in an inflamed appendix will usually warrant appendectomy, as appendicoliths have been known to cause a significant failure rate of non-operative management of appendicitis, which is due to the bacteria in the appendicolith forming a nidus [43]. Furthermore, an appendicolith within an inflamed appendix can traverse its wall, leading to perforation and other significant complications [44]. More information on appendicolith can be found in this recent narrative review [44].

Figure 8.

An appendicolith in a patient with complicated (perforated) appendicitis. A: Shows a transverse sonogram of the appendix base (long arrow) with an appendicolith (arrow head) showing a ‘strong’ posterior acoustic shadow (x), periappendiceal mesenteric oedema, complex periappendiceal collection (star), and mild wall thickening of the adjacent terminal ileum (three short arrows) anteriorly. b: Shows the colour Doppler mode in the same patient with a ‘twinkling artefact’ seen emanating from the appendicolith and mild wall hypervascularity of the terminal ileum secondary to the inflamed appendix. The ultrasound diagnosis was complicated appendicitis with possible perforation, confirmed in surgery and histopathology the next day.

8. Complicated (gangrenous and perforated) appendicitis

8.1 Overview

Complicated appendicitis mainly comprises gangrenous and perforated appendicitis with appendiceal necrosis [45]. These are known to lead to failed antibiotics management; therefore, surgery is always required, which can be either laparoscopic or open appendectomy, depending on the degree of complication [45, 46, 47]. In light of this, imaging plays a vital role in their differentiation [47]. Although there is a low sensitivity of imaging, recorded in literature, in distinguishing between uncomplicated and complicated appendicitis; with US even lower than CT, recognising the standard US features can make a difference in the patient’s diagnostic journey while averting unnecessary radiation exposure, particularly in children and young adults [48].

8.2 Ultrasound features

The primary US features [46] of complicated appendicitis (Figure 9) include;

• An inflamed appendix measuring above 0.6 cm (usually above 1.0 cm) in AP calibre that can sometimes contain heterogeneous (purulent) materials

• A loss of appendiceal wall stratification, particularly loss of the submucosal layer

• The absence of wall vascularity

• The presence of an appendicolith (usually large in size)

• The visualisation of an appendiceal wall defect or mucosal ulceration and some periappendiceal fluid

• The presence of periappendiceal heterogeneous collection/abscess.

Figure 9.

Sonograms in two different patients with perforated and gangrenous appendicitis confirmed surgically and histopathologically. A: Shows a significantly inflamed appendix measuring 18 mm AP (not shown in the image) in a longitudinal orientation with an abnormal wall layering, including a loss of the echogenic submucosal layer and significant echogenic periappendiceal mesenteric oedema. Also, note the small area in the posterior surface of the appendix with tracking fluid (FF) from a likely compromised serosa, which raised the suspicion of perforated appendicitis on ultrasound. b: Shows the same appendix in transverse orientation with significant periappendiceal mesenteric oedema and an abnormal appendix wall stratification. c: Shows a longitudinal image of another patient with a gangrenous appendix filled with purulent content. This appendix is thin-walled and has lost its submucosa layer, with its lumen filled with echogenic (purulent) content. No wall or luminal vascularity was seen, although not shown in the image; this patient also had a large appendicolith at the base of the appendix that likely caused the complication.

The secondary US features [46] include:

• The presence of significant mesenteric oedema

• The presence of a sizeable unexplainable mass-like structure seen where the appendix is expected to be, without visualising the appendix

• The presence of some free fluid in the abdomen and pelvis.

In addition, tiny echogenic punctate foci within the wall of the appendix (intramural) have been associated with possible appendix necrosis and gangrene (Figure 9c). However, the ultrasound examiner must take care not to misidentify this sign with the bowel gas in the adjacent normal bowel structures [49]. Furthermore, the loss of the normal appendiceal wall stratification (Figure 8a and b) and the visualisation of a defect in the appendix wall or mucosal ulceration with a close relation to a collected periappendiceal fluid (Figure 9a) or collection (Figure 8a) significantly raises the suspicion of perforation on US [50, 51].

9. Other pathologies with similar symptoms

In practice, not every patient presenting with the symptoms of appendicitis ends up having appendicitis. There are many other disease conditions that are either bowel-related or extra-bowel pathologies with symptoms that mimic appendicitis in the abdomen and pelvis. Some commonly encountered bowel-related appendicitis-mimicking pathologies diagnosed on ultrasound are; Crohn’s disease and ulcerative colitis (IBD), diverticulitis, caecitis, terminal ileitis, ileocecitis, colitis, mesenteric adenitis, and intussusception [52]. These all have individual identifying features on ultrasound that help distinguish the diagnosis from appendicitis; however, this is beyond the scope of this chapter.

Meanwhile, some non-bowel-related pathologies encountered on US with symptoms that mimic appendicitis are; cholelithiasis with or without cholecystitis, urinary tract infection, pyelonephritis, nephrolithiasis/urolithiasis, and gynaecological (including ovarian-related) pathologies [53]. It is the responsibility of the ultrasound examiner to identify and properly diagnose these conditions when visualised on ultrasound or determine if the appearances are inconclusive, therefore promptly suggesting other diagnostic imaging examinations to prevent unanticipated complications.

10. Summary

Ultrasound is a handy and safe tool in diagnosing appendicitis with a consistently improving diagnostic efficacy in line with technological advancement and increased availability of information. However, due to its significant operator dependence, a high degree of training and competence is required, particularly in the area of diagnosis of appendicitis. In addition, certain factors improve the sensitivity and specificity of ultrasound in examining for appendicitis; this includes the use of good scanning equipment, an understanding of the bowel ultrasound anatomy and various (typical and atypical) presentations and complications of appendicitis, and the adoption of the proper scanning techniques. This chapter discussed the scanning techniques and ultrasound appearances commonly encountered in patients with appendicitis, and it also presented some relevant sonograms of normal and abnormal appendixes that were confirmed surgically and histologically.

Acknowledgments

Many thanks L.D. Sander and Dr. Babalola Afolabi for their effort in proofreading the manuscript of this chapter.

Conflict of interest

No conflict of interest.