Appendiceal mucosal hyperplasia is hyperplastic proliferation of the mucosal epithelium lining the appendix lumen. It is the most common benign appendiceal epithelial lesion, incidentally found in 0.5-1% of appendectomy specimens. Lesions are usually <5 mm and remain at subclinical size on CT and MRI. Hyperplastic polyps are part of the serrated polyp family, but appendiceal hyperplasia has extremely low risk of progression along the serrated neoplasia pathway, unlike colonic hyperplastic polyps. Rarely, it may cause luminal obstruction triggering secondary acute appendicitis — in this scenario, the clinical presentation is indistinguishable from appendicitis and diagnosis is made by pathologic examination. In rare cases when visible on CT, it presents as focal appendiceal wall thickening with minimal or no enhancement.
Age Range
30-70
Peak Age
55
Gender
Equal
Prevalence
Rare
Appendiceal mucosal hyperplasia develops from excessive proliferation of mucosal epithelium. In hyperplastic polyps, goblet cells and absorptive cells proliferate more than normal, causing crypt elongation and branching — but without dysplastic changes. This proliferation likely develops as a response to chronic low-grade mucosal irritation. Fecalith retention, chronic low-grade inflammation, and local mucosal damage are among triggering factors. On imaging, this pathophysiology manifests as very small size (<5 mm), minimal vascularity, and absence of enhancement — because the lesion does not reach the size to trigger neovascularization and does not contain atypical cell proliferation. Diffusion restriction is also not expected due to low cellularity. When the lesion grows into the lumen, it can cause luminal obstruction — in this case, increased intraluminal pressure, mucosal ischemia, and bacterial translocation trigger secondary appendicitis, and appendicitis pathophysiology takes over.
The most characteristic feature of appendiceal mucosal hyperplasia is paradoxically its 'invisibility' on imaging. The lesion is usually <5 mm, below the spatial resolution of CT and MRI. Diagnosis is almost always made by pathologic examination after appendectomy. On CT, the appendix appears normal — no dilation, fat stranding, or increased enhancement. This 'negative imaging finding' is meaningful in the clinical context (patient planned for appendectomy).
Focal, asymmetric thickening in appendiceal wall. Usually localized near the appendiceal base. Wall thickness may be 3-5 mm. Luminal diameter usually remains normal (<6 mm) and appendix does not appear dilated.
Report Sentence
Focal asymmetric thickening is seen in the appendiceal wall; clinical correlation and pathologic evaluation if indicated are recommended.
Minimal or no enhancement in the area of focal wall thickening. No periappendiceal fat stranding is present. Periappendiceal area is clean.
Report Sentence
No significant enhancement or periappendiceal inflammatory changes are seen in the thickened appendiceal wall.
Mildly hyperintense or isointense focal thickening in appendiceal wall on T2. Marked T2 hyperintensity is not expected — no mucinous content or significant edema. No diffusion restriction either.
Report Sentence
Focal thickening showing mild T2 signal increase is seen in the appendiceal wall with no diffusion restriction detected.
Small (<5 mm), isoechoic or mildly hypoechoic polypoid lesion in appendix lumen. Lumen is usually of normal diameter and appendiceal compressibility is preserved. No acoustic shadow (no calcification).
Report Sentence
A polypoid lesion of low echogenicity measuring approximately ___ mm is seen within the appendix lumen with no significant vascularity on Doppler examination.
No or minimal flow signal within the lesion on color Doppler and power Doppler examination. Periappendiceal area is clean, no periappendiceal hyperechoic fat increase.
Report Sentence
No vascularity is detected on Doppler examination of the polypoid lesion in the appendix lumen; no evidence of malignant vascularity.
Appendix diameter is usually within normal limits (<6 mm). No dilation expected unless luminal obstruction develops. Periappendiceal fat tissue is clean.
Report Sentence
The appendix is of normal caliber measuring ___ mm in diameter; no periappendiceal inflammatory changes are seen.
Criteria
Most common type. Goblet and absorptive cell increase, crypt elongation, serrated crypt architecture. No dysplasia. Usually <5 mm, solitary.
Distinct Features
Malignant transformation risk is negligibly low. Appendectomy is curative. No additional follow-up or treatment needed. Unlike colonic hyperplastic polyps, serrated neoplasia pathway risk is negligible.
Criteria
Rare. Hyperplastic polyp has reached size causing luminal obstruction. Secondary acute appendicitis develops. Appendicitis findings predominate on CT.
Distinct Features
Indistinguishable from acute appendicitis on CT — diagnosis made by pathologic examination after appendectomy. Clinical presentation is acute abdominal pain. Appendectomy treats both the appendicitis and underlying hyperplasia.
Criteria
Rarely, more than one hyperplastic focus may be found in the appendix. May cause diffuse mucosal thickening. Association with hereditary polyposis syndromes should be investigated.
Distinct Features
Hereditary polyposis syndrome (hyperplastic polyposis syndrome) should be considered in the presence of concurrent colonic polyps. Colon screening with colonoscopy is recommended. Appendectomy is sufficient but colon follow-up may be needed.
Distinguishing Feature
Appendiceal carcinoid presents as a well-defined submucosal nodule with intense arterial enhancement. Hyperplasia shows no or minimal enhancement and is usually invisible on CT. Carcinoid shows increased vascularity on Doppler.
Distinguishing Feature
Mucinous neoplasm shows low-density luminal dilation (mucin accumulation), wall calcification, and possible peritoneal spread. Hyperplasia does not cause luminal distension and has no calcification. Appendix diameter is significantly increased (>15 mm) in mucinous neoplasm.
Distinguishing Feature
Acute appendicitis shows dilated appendix (>6 mm), periappendiceal fat stranding, increased wall enhancement, and possible appendicolith. Hyperplasia is distinguished by absence of inflammatory findings — normal appendix diameter, no fat stranding, no increased enhancement.
Distinguishing Feature
Adenomatous polyp has dysplastic potential and tends to be larger. Enhancement is more prominent than hyperplasia. Definitive differentiation is made by histopathologic examination — hyperplasia has no dysplasia, adenoma has dysplasia.
Urgency
routineManagement
surgicalBiopsy
Not NeededFollow-up
no-follow-upAppendiceal mucosal hyperplasia is a benign lesion with extremely low malignant transformation risk. It is curatively treated with appendectomy — no additional treatment or follow-up is needed when incidentally detected. When secondary appendicitis develops, emergency surgical indication exists, but treatment is appendectomy anyway. Absence of dysplasia should be confirmed on pathologic examination — if dysplasia is present, it should be reclassified as adenomatous change and colon screening is recommended. Hereditary polyposis syndrome should be investigated in the presence of concurrent colonic polyps.
Appendiceal mucosal hyperplasia is a benign lesion with extremely low risk of malignant transformation. It is curatively treated with appendectomy. No additional treatment or follow-up is needed when incidentally detected. Rarely, it may cause luminal obstruction triggering secondary appendicitis.