Appendiceal mucocele

Changed by Bruno Di Muzio, 9 Aug 2017

Updates to Synonym Attributes

Title was changed:
Appendiceal mucocelemucocoele

Updates to Article Attributes

Title was changed:
Appendiceal mucocoelemucocele
Body was changed:

Appendiceal mucocoelesmucoceles occur when there is an abnormal accumulation of mucus withinmucin causing abnormal distention of the appendix. The tenacious and viscous mucus causesThey are due to either nonneoplastic process, such as luminal obstruction of the appendiceal neck and results in dilatation of the lumen, or by mucin-secreting epithelial tumours.

Epidemiology

The reported prevalence at appendectomy is 0.2-0.3%. They are thought to typically present in the middle aged individuals, particularly considering the epidemiology of the mucinous neoplasms.

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 lesions:

Variants
  • myxoglobulosis: seen a rare mucocele variant seen as 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
Barium enema

If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocoele, 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

  • .  
  • the finding of curvilinear mural calcification suggests the diagnosis, but is seen in less than 50% of cases 
  • intra-luminal bubbles of gas, or an air-fluid level within a mucocele suggestindicate the presence of superinfection, which can occur in both benign and malignant mucocoelesmucoceles
  • 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.

Typical and the typical signal characteristics include:

  • T1: depending on the mucin concentration, the signal may be variablyvariable, from hypointense to isointense 9
  • T2: hyperintense

Treatment and prognosis

Treatment is usually surgical.

Complications

Differential diagnosis

Differentiating benign (non-neoplastic mucocoele 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 mucocoeles</strong> occur when there is abnormal accumulation of mucus within the <a href="/articles/appendix">appendix</a>. The tenacious and viscous mucus causes obstruction of the appendiceal neck and results in dilatation of the lumen.</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.</p><h4>Pathology</h4><p>The term mucocele is simply a macroscopic description of an appendix that is grossly distended by mucus <sup>7</sup>. They result from chronic appendiceal obstruction that may be caused by either benign or malignant lesions:</p><ul>
  • +<p><strong>Appendiceal mucoceles</strong> occur when there is an abnormal accumulation of mucin causing abnormal distention of the <a href="/articles/appendix">appendix</a>. They are due to either nonneoplastic process, such as luminal obstruction, or by 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 the 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 lesions:</p><ul>
  • -<li>adjacent caecal tumour</li>
  • +<li>adjacent caecal tumour obstructing the appendiceal orifice </li>
  • -<a href="/articles/myxoglobulosis">myxoglobulosis</a>: seen as with multiple small intraluminal globules which can calcify and produce 1-10 mm mobile calcifications</li></ul><h4>Radiographic features</h4><h5>Fluoroscopy: barium enema</h5><p>If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocoele, the associated mass effect can cause indentation or lateral displacement of the <a href="/articles/caecum">caecum</a>.</p><h5>Ultrasound</h5><p>Typically cystic mass with variable internal echogenicity <sup>8</sup>. The presence of an "onion sign" (sonographic layering within a cystic mass) is considered a highly suggestive feature <sup>2,6</sup>.</p><h5>CT</h5><ul>
  • -<li>typically seen as a well-circumscribed, low-attenuation, spherical or tubular mass contiguous with the base of the caecum</li>
  • -<li>the finding of curvilinear mural calcification suggests the diagnosis, but is seen in less than 50% of cases </li>
  • -<li>intra-luminal bubbles of gas, or an air-fluid level within a mucocele suggest the presence of superinfection, which can occur in both benign and malignant mucocoeles</li>
  • -</ul><h5>MRI</h5><p>Seen as a rounded right iliac fossa mass.</p><p>Typical signal characteristics include:</p><ul>
  • +<a href="/articles/myxoglobulosis">myxoglobulosis</a>: a rare mucocele variant seen as with multiple small intraluminal globules which can calcify and produce 1-10 mm mobile calcifications</li></ul><h4>Radiographic features</h4><h5>Plain radiograph</h5><p>It can be characterised by a right iliac fossa mass with peripheral calcifications <sup>12</sup>. </p><h5>Fluoroscopy</h5><h6>Barium enema</h6><p>If a contrast examination is performed, there is usually non-filling or partial-filling of the appendix. Where there is a large mucocoele, the associated mass effect can cause the indentation or lateral displacement of the <a href="/articles/caecum">caecum</a>.</p><h5>Ultrasound</h5><p>Typically cystic mass with variable internal echogenicity <sup>8</sup>. The presence of an "onion sign" (sonographic layering within a cystic mass) is considered a highly suggestive feature <sup>2,6</sup>. Acoustic shadowing may be present due to the mural calcifications <sup>12</sup>. </p><h5>CT</h5><p>They are typically seen as a well-circumscribed, low-attenuation, spherical or tubular mass contiguous with the base of the caecum.  </p><ul>
  • +<li>curvilinear mural calcification suggests the diagnosis but is seen in less than 50% of cases </li>
  • +<li>intra-luminal bubbles of gas or an air-fluid level within a mucocele indicate the presence of superinfection, which can occur in both benign and malignant mucoceles</li>
  • +<li>mural nodularity and irregular wall thickening are suggestive of a malignant process <sup>12</sup>
  • +</li>
  • +</ul><p>When identifying a mucocele on CT, search for extraluminal mucin is mandatory, which are low-attenuated deposits commonly seen in certain locations <sup>12</sup>:</p><ul>
  • +<li>periappendiceal space </li>
  • +<li>peritoneal cavity</li>
  • +<li>at the surface of abdominal viscera, including ovaries and bowel</li>
  • +</ul><h5>MRI</h5><p>Seen as a rounded right iliac fossa mass and the typical signal characteristics include:</p><ul>
  • -<strong>T1:</strong> depending on the mucin concentration, the signal may be variably hypointense to isointense <sup>9</sup>
  • +<strong>T1:</strong> depending on the mucin concentration, the signal may be variable, from hypointense to isointense <sup>9</sup>
  • -<li>rupture: may lead to <a href="/articles/pseudomyxoma-peritonei">pseudomyxoma peritonei</a> if the underlying cause is neoplastic <sup>11</sup>
  • +<li>rupture: may lead to <a href="/articles/pseudomyxoma-peritonei">pseudomyxoma peritonei</a> if the underlying cause is neoplastic <sup>11,12</sup>
  • -<li>can act as a lead point and lead to an <a href="/articles/intussusception">ileo-colic intussusception</a> <sup>9</sup>
  • +<li>can act as a lead point and result in an <a href="/articles/intussusception">ileo-colic intussusception</a> <sup>9</sup>
  • -</ul><h4>Differential diagnosis</h4><p>Differentiating benign (non-neoplastic mucocoele and mucinous cystadenoma) and malignant (mucinous cystadenocarcinoma) appendiceal lesions can be difficult. Wang et al <sup>10</sup> found a statistically significant difference in wall irregularity and soft-tissue thickening between malignant and benign cases. </p>
  • +</ul><h4>Differential diagnosis</h4><p>Differentiating benign (non-neoplastic mucocoele and mucinous cystadenoma) and malignant (mucinous cystadenocarcinoma) appendiceal lesions can be difficult. Wang et al. <sup>10</sup> found a statistically significant difference in wall irregularity and soft-tissue thickening between malignant and benign cases. </p>

References changed:

  • 12. Leonards LM, Pahwa A, Patel MK et-al. Neoplasms of the Appendix: Pictorial Review with Clinical and Pathologic Correlation. Radiographics : a review publication of the Radiological Society of North America, Inc. 37 (4): 1059-1083. <a href="https://doi.org/10.1148/rg.2017160150">doi:10.1148/rg.2017160150</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/28598731">Pubmed</a> <span class="ref_v4"></span>

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