Appendiceal mucocele
Updates to Article Attributes
Appendiceal mucoceles occur when there is an abnormal accumulation of mucin causing abnormal distention of the vermiform appendix. They are due due to either avarious neoplastic or non-neoplastic process, such as luminal obstruction, or mucin-secreting epithelial tumourscauses.
Epidemiology
The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middle-aged individuals, particularly considering the epidemiology of the mucinous neoplasms. Though carcinoid tumor is the most common primary appendiceal neoplasm in surgical pathology series, mucoceles due to neoplasms are the most common appendiceal tumors detected on imaging.7
Pathology
The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus 7,12. They result from the chronic appendiceal obstruction that may be caused by either benign or malignant lesionlesions, categorized into four histologic types:
- mucus retention cyst (due to obstruction most commonly by a fecalith)
- mucosal hyperplasia
(most common11 -
mucinous neoplasms appendiceal carcinoidadjacent caecal tumour obstructing the appendiceal orifice
Variants
- myxoglobulosis: a rare mucocele variant seen with multiple small intraluminal globules which can calcify and produce 1-10 mm mobile calcifications
Radiographic features
Plain radiograph
It can be characterised by a right iliac fossa mass with peripheral calcifications 12.
Fluoroscopy
Barium enema
If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocele, the associated mass effect can cause the indentation or lateral displacement of the caecum.
Ultrasound
Typically cystic mass with variable internal echogenicity 8. The presence of an "onion sign" (sonographic layering within a cystic mass) is considered a highly suggestive feature 2,6. Acoustic shadowing may be present due to the mural calcifications 12.
CT
They are typically seen as a well-circumscribed, low-attenuation, spherical or tubular mass contiguous with the base of the caecum.
- curvilinear mural calcification suggests the diagnosis but is seen in less than 50% of cases
- intra-luminal bubbles of gas or a gas-fluid level within a mucocele indicate the presence of superinfection, which can occur in both benign and malignant mucoceles
- mural nodularity and irregular wall thickening are suggestive of a malignant process 12
When identifying a mucocele on CT, search for extraluminal mucin is mandatory, which are low-attenuated deposits commonly seen in certain locations 12:
- periappendiceal space
- peritoneal cavity
- at the surface of abdominal viscera, including ovaries and bowel
MRI
Seen as a rounded right iliac fossa mass and the typical signal characteristics include:
- T1: depending on the mucin concentration, the signal may be variable, from hypointense to isointense 9
- T2: hyperintense
Treatment and prognosis
Treatment is usually surgical.
Complications
- rupture: may lead to pseudomyxoma peritonei
if(mucinous ascites) if the underlying cause is neoplastic 11,12 - can act as a lead point and result in an ileocolic intussusception 9
Differential diagnosis
Differentiating benign (non-neoplastic mucocele and mucinous cystadenoma) and malignant (mucinous cystadenocarcinoma) appendiceal lesions can be difficult. Wang et al. 10 found a statistically significant difference in wall irregularity and soft-tissue thickening between malignant and benign cases.
-<p><strong>Appendiceal mucoceles</strong> occur when there is an abnormal accumulation of mucin causing abnormal distention of the <a href="/articles/appendix-1">appendix</a>. They are due to either a non-neoplastic process, such as luminal obstruction, or mucin-secreting epithelial tumours.</p><h4>Epidemiology</h4><p>The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middle-aged individuals, particularly considering the epidemiology of the mucinous neoplasms. </p><h4>Pathology</h4><p>The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus <sup>7,12</sup>. They result from the chronic appendiceal obstruction that may be caused by either benign or malignant lesion:</p><ul>-<li>mucosal hyperplasia (most common <sup>11</sup>)</li>-<li>mucinous neoplasms<ul>-<li><a href="/articles/mucinous-cystadenoma-of-appendix">mucinous cystadenoma of appendix </a></li>- +<p><strong>Appendiceal mucoceles</strong> occur when there is an abnormal accumulation of mucin causing abnormal distention of the vermiform <a href="/articles/appendix-1">appendix</a> due to various neoplastic or non-neoplastic causes.</p><h4>Epidemiology</h4><p>The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in middle-aged individuals, particularly considering the epidemiology of the mucinous neoplasms. Though carcinoid tumor is the most common primary appendiceal neoplasm in surgical pathology series, mucoceles due to neoplasms are the most common appendiceal tumors detected on imaging.<sup>7</sup></p><h4>Pathology</h4><p>The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus <sup>7,12</sup>. They may be caused by either benign or malignant lesions, categorized into four histologic types:</p><ul>
- +<li>mucus retention cyst (due to obstruction most commonly by a fecalith)</li>
- +<li>mucosal hyperplasia (analogous to a hyperplastic colonic polyp)</li>
- +<li>
- +<a href="/articles/mucinous-cystadenoma-of-appendix">mucinous cystadenoma of appendix</a> (most common<sup>11</sup>)</li>
-</ul>-</li>-<li><a href="/articles/appendiceal-carcinoid">appendiceal carcinoid</a></li>-<li>adjacent caecal tumour obstructing the appendiceal orifice </li>-<li>rupture: may lead to <a href="/articles/pseudomyxoma-peritonei">pseudomyxoma peritonei</a> if the underlying cause is neoplastic <sup>11,12</sup>- +<li>rupture: may lead to <a href="/articles/pseudomyxoma-peritonei">pseudomyxoma peritonei</a> (mucinous ascites) if the underlying cause is neoplastic <sup>11,12</sup>
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