Keywords
appendix - positions - MDCT - in vivo
Introduction
The appendix, part of the gastrointestinal system, typically resides in the right
iliac fossa. As a vestigial structure, the vermiform appendix emerges during the developmental
phase from the cecum, exhibiting a remarkably diverse anatomical location.
The appendix can assume various positions within the abdomen, deviating from its typical
location in the lower right quadrant. These atypical positions can result in atypical
clinical symptoms that may not align with the classic presentation of appendicitis.[1]
[2] In pelvic appendicitis, suprapubic pain and urinary frequency may predominate, and
positive rectal or vaginal tenderness and obturator signs are common. Similarly, cases
of subhepatic appendicitis can present with pain in the right upper quadrant and epigastric
region in sharp contrast to the right lower quadrant pain typically seen in a more
commonly placed appendix.[3] Therefore, understanding the spectrum of appendiceal positional variations assumes
paramount importance, particularly in cases where appendicitis manifests with atypical
clinical features.[4]
[5] In such patients, imaging studies play a significant role in preoperative diagnosis
and to guide the laparoscopic surgeons in planning the proper treatment.[6]
Despite postmortem studies and conventional surgical and anatomical textbooks commonly
citing retrocecal as the most prevalent position, such assertions warrant empirical
validation.[7]
[8]
[9]
[10]
[11] Hence, our study endeavors to delineate the prevailing position of the appendix
on computed tomography (CT) scans and ascertain its concordance with existing literature,
thereby augmenting our understanding of this anatomical entity.
Materials and Methods
This cross-sectional study was conducted with approval from the institutional ethics
committee. The requirement for obtaining consent has been waived by the institutional
ethics committee, given that we are acquiring anonymized data for a cross-sectional
study.
Selection and Description of Participants
All patients referred for abdominal CT scans, whether plain or plain and contrast
studies, from various clinical departments and who have given consent, were eligible
for inclusion in this study. To ensure robustness, we calculated the minimum sample
size required to be 1,068, employing a population proportion of 0.5 and an absolute
precision of 0.03.
Inclusion criteria stipulated that patients must be aged 18 years and above. Exclusion
criteria encompassed patients with disseminated abdominal malignancies, infections,
or trauma causing anatomical distortion, intra-abdominal pathologies exerting a mass
effect on the right colon, malrotation of the gut, and individuals who had previously
undergone appendicectomy.
Technical Information
Imaging procedures were performed in elective patients on Somatom Definition AS+ 128
slice multidetector computed tomography (MDCT) scanner (Siemens Medical Solutions,
Forchheim, Germany). Patients were kept fasting for 4 hours prior to the scan. Premedication,
including Perinorm 2 mL (metoclopramide 10 mg) and Avil 1 mL (pheniramine maleate
22.75 mg) was given intravenously (IV) to avoid contrast-induced allergic reactions.
IV methylprednisolone was given to patients with a history of allergies. Patients
were briefed in their vernacular language regarding machine instructions for breath
holding and contrast injection via the pressure injector.
The scan was acquired according to the following protocol ([Table 1]).
Table 1
Scan protocol
|
Patient position
|
Supine position, head first, on the gantry table, with their hands placed above the
head and abdomen centered within the gantry
|
|
Tube voltage (kVp)
|
140
|
|
Tube current (mAs)
|
220
|
|
Pitch
|
0.6
|
|
Gantry speed
|
0.5 s per rotation
|
|
Scan extent
|
From the dome of the diaphragm to the coccyx
|
|
Scan direction
|
Craniocaudal
|
|
Field of view
|
350–400 mm
|
|
Slice thickness
|
5 mm (1.5-mm-thick reconstruction for plain scans and 1-mm reconstruction for contrast
scans)
|
|
Slice interval
|
1 mm
|
|
Reconstruction algorithm
|
Kernel B30f smooth
|
|
Oral contrast
|
800 mL of water 1 hour before the scan, followed by a table dose of 200 mL of water
just before the scan
|
|
Intravenous contrast
|
1.Noncontrast scan
2. Biphasic arterial and venous acquisition
• Contrast volume:2 mL/kg nonionic iodinated contrast injected at a speed of 4 mL/s
through a pressure injector (Medrad, United States)
• Bolus tracking: abdominal aorta
• Arterial phase: after a delay of 6 s following bolus tracking
• Venous phase: after a delay of 40 s from bolus tracking
Subsequently, axial, sagittal, and coronal–multiplanar images were reconstructed in
kernel B30f smooth and reviewed in soft tissue window
|
Image Interpretation
The images were analyzed by two radiologists in consensus, each having a minimum of
5 years of experience in abdominal imaging. The appendix was traced along its entire
length, from origin to tip. Key parameters including the location of the ostium, diameter,
wall thickness, and position based on the tip's location were recorded. The ostium
of the appendix was characterized based on its origin from the cecal wall, categorized
as anterior, posterior, lateral, medial, or inferior. Wall thickness was measured
at the maximum diameter of the appendix.
The position of the appendix was categorized as follows: (1) retrocecal or retrocolic
position (posterior to the cecum or the lower ascending colon, or both) ([Figs. 1], [2A]), (2) pelvic or descending position (suspended over the pelvic brim) ([Figs. 1], [2B]), (3) subcecal location (below the cecum) ([Figs. 1], [2C]), (4) preileal position (anterior to the terminal ileum) ([Figs. 1], [2D]), (5) postileal position (posterior to the terminal ileum) ([Figs. 1], [2E]), (6) paracecal position (adjacent to the cecum) ([Figs. 1], [2F]), and (7) subhepatic position ([Fig. 2G]).
Fig. 1 Various positions of appendix in relation to cecum and terminal ileum.
Fig. 2 Appendiceal positions as seen on computed tomography. (A) Right (Rt) parasagittal reconstruction shows retrocecal appendix (arrow). (B) On coronal section pelvic appendix (arrow) is seen hanging over Rt iliac vessels.
(C) Coronal section shows appendix in subcecal position. (D) A preileal appendix is seen on axial section. (E) Axial section shows a postileal appendix passing superiorly behind terminal ileum.
(F) The paracecal appendix is seen on axial section. (G) A coronal maximum intensity projection shows appendix in subhepatic location.
Statistical Analysis
Data were systematically collected in a predesigned Microsoft Excel spreadsheet. Subsequently,
the numbers and relative frequencies of appendiceal positions and origins were computed.
Diameter and wall thickness measurements were recorded for each patient. Furthermore,
the mean and range of appendix diameter and appendiceal wall thickness were calculated.
Results
A total of 1,068 patients were enrolled in the study. There were 624 men and 444 women.
The age range was 18 to 76 years. The median age was 48 years.
Among these 1,068 cases, 71 appendices (6.6%) were subcecal, 13 (1.2%) were paracecal,
234 (21.9%) were in the pelvic region, 351 (32.9%) were postileal, 72 (6.7%) were
preileal, 304 (28.5%) were retrocecal, and 23 (2.2%) were subhepatic ([Table 2]).
Table 2
Frequency distribution of in vivo position of appendix
|
Position of appendix
|
Frequency
|
%
|
|
Subcecal
|
71
|
6.6
|
|
Paracecal
|
13
|
1.2
|
|
Pelvic
|
234
|
21.9
|
|
Postileal
|
351
|
32.9
|
|
Preileal
|
72
|
6.7
|
|
Retrocecal
|
304
|
28.5
|
|
Subhepatic
|
23
|
2.2
|
|
Total
|
1,068
|
100
|
Regarding the origin of the appendix ([Table 3]), the most common was found to be posteromedial, in 638 cases (59.7%). Other origins
exhibited the following distribution: 1 (0.1%) anterior, 68 (6.4%) inferior, 11 (1%)
inferomedial, 1 (0.1%) lateral, 224 (21%) medial, 124 (11.6%) posterior, and 1 (0.1%)
postileal.
Table 3
Frequency distribution of origin of appendix
|
Origin of appendix
|
Frequency
|
%
|
|
Anterior
|
1
|
0.1
|
|
Inferior
|
68
|
6.4
|
|
Inferomedial
|
11
|
1.00
|
|
Lateral
|
1
|
0.1
|
|
Medial
|
224
|
20.9
|
|
Posterior
|
124
|
11.6
|
|
Posteromedial
|
638
|
59.7
|
|
Postileal
|
1
|
0.1
|
|
Total
|
1,068
|
100
|
In our study, the mean maximum outer diameter of the appendix was determined to be
5.31 ± 1.2 mm, with a range of 1.3 to 15 mm. Notably, 235 patients (22%) displayed
a diameter exceeding 6.0 mm.
The mean appendiceal wall thickness was calculated as 1.68 ± 0.6 mm, ranging from
0.5 to 7 mm. Of significance, only 39 appendices (3.7%) exhibited a wall thickness
surpassing 3.0 mm.
Discussion
In Wakeley's anatomopathological examination of 10,000 deceased subjects,[7] the vermiform appendix exhibited retrocecal and retrocolic positioning in 65.28%
of cases, pelvic placement in 31.01%, subcecal positioning in 2.26%, preileal positioning
in 1%, and postileal positioning in 0.4%.
Studies utilizing CT scans have revealed that the prevailing positions of the appendix
include the retroileal,[9]
[10] deep pelvic,[11]
[12] or subcecal types.[12] Lee et al[12] conducted an investigation involving 1,157 subjects to ascertain the in vivo location
of the vermiform appendix via MDCT scans. Their findings challenged the conventional
belief that the retrocecal appendix is the most frequent, instead indicating a higher
incidence of the appendix in subcecal and deep pelvic positions. Moreover, they noted
that the relative frequency of various appendix positions can vary based on patient
gender and pathological conditions.
Similarly, Willekens et al[13] examined 186 individuals undergoing abdominal CT scans without suspicion of acute
appendicitis. Their analysis revealed that the pelvic location accounted for 66% of
appendices, underscoring the variability in appendix positioning observed across studies
and patient populations.
Oh et al[14] conducted an assessment of normal appendices using MDCT scans in 427 consecutive
adult patients. They categorized the positions of normal appendices into five types:
type I (postileal and medial paracecal), type II (subcecal), type III (retrocecal
and retrocolic or laterocolic), type IV (preileal and medial colic), and type V (lower
pelvic cavity). Their analysis revealed the frequency of these types as follows: type
I (n = 187; 44%), type II (n = 78; 18%), type III (n = 92; 22%), type IV (n = 39; 9%), and type V (n = 31; 7%).
Similarly, Picken et al[15] investigated the normal vermiform appendix in 100 patients undergoing abdominal
CT scans, finding it predominantly situated in a retroileal position.
Moreover, recent studies employing various medical imaging techniques and laparoscopy
have produced findings that challenge historical conventions regarding the position
of the appendix, as highlighted in several recent studies.[13]
[14]
[16]
Peletti and Baldisserotto[16] conducted a study involving 107 children who underwent gray-scale ultrasound (USG)
scanning. They classified normal and abnormal appendices with the following distributions:
54.4 and 39.3% were located in the midpelvic region, 27.2% and 28.6% were retrocecal,
11.4% and 17.8% were deep pelvic, and 6.8% and 14.3% were abdominal.
Yabunaka et al[17] evaluated 788 adult patients with normal appendices using sonography. They categorized
the appendix locations based on the appendiceal tip, identifying it as abdominal in
37 (9.5%) cases, pelvic in 291 (75%), retrocecal in 23 (6.0%), and exhibiting a midline
extension in 37 (9.5%).
In a laparoscopic study involving 303 adults, Ahmed et al[18] concluded that the position of the vermiform appendix was pelvic in 155 (51.2%)
patients, preileal in 9 (3.0%), paracecal in 11 (3.6%), postileal in 67 (22.1%), and
retrocecal in 61 (20.1%) patients.
Providing preoperative information to the surgeon regarding the location of the inflamed
appendix facilitates preoperative planning for appropriate incisions in open appendectomy,
thereby reducing the incidence of postoperative complications such as pain, hematoma,
and incision site hernia.[19] However, in laparoscopic appendectomy, while knowledge of the appendix's location
may contribute to reduced operative time and less aggressive search efforts, its importance
may be relatively diminished.[12]
[20]
CT scans have demonstrated superior diagnostic performance compared with USG in assessing
the appendix.[21]
[22] Standard abdominopelvic CT with IV contrast, with or without oral and rectal contrast,
is the preferred investigative modality.[13]
[21]
The comparison of previous studies has been hindered by differing classifications
and definitions. In our study, we considered seven appendiceal positions, including
six originally described by Wakeley et al. Our findings reveal that the postileal,
retrocecal, and pelvic positions are the most common, with subcecal, paracecal, preileal,
and subhepatic positions being less frequent.
Twenty-two percent (235 patients) exhibited an appendiceal diameter exceeding 6 mm,
aligning with findings from the study by Willekens et al,[13] indicating that a 6.0 mm diameter alone may not suffice for diagnosing appendicitis
in the absence of other CT indicators.
However, only 3.7% of patients displayed a wall thickness surpassing 3.0 mm, suggesting
that a wall thickness > 3.0 mm might serve as a more reliable indicator of inflammation,
necessitating further validation.
The predominant origins of the appendix were posteromedial (59.73%), medial (21%),
and posterior (11.61%), whereas anterior, inferior, inferomedial, lateral, and postileal
origins were less frequent. During development, the appendiceal origin undergoes counter-clockwise
rotation, resulting in the prevalence of posteromedial, medial, and posterior origins.[7]
Conclusion
Contrary to traditional teachings, the common positions of the appendix observed in
vivo on MDCT are, in descending order of prevalence, postileal, retrocecal, and pelvic
with other locations being less common. Additionally, the current study elucidates
a significant variance in the diameters of the appendix among cases of appendicitis,
a finding incongruous with the existing 6-mm threshold utilized in diagnosing acute
appendicitis. Consequently, this underscores the necessity for further investigations
aimed at establishing a revised diagnostic cutoff for acute appendicitis.
