Appendicolith (fecaloid) is an intraluminal structure formed by progressive calcification of fecal material accumulating in the appendix lumen. Fecal material, mucosal secretions, and inorganic salts (calcium phosphate, calcium carbonate) accumulate in layers, developing concentric calcification. Plays a critical role in appendicitis pathogenesis — appendicolith is present in approximately 35% of appendicitis cases, and its presence increases complicated appendicitis (perforation) risk 2-3 fold. Isolated appendicolith (without appendicitis findings) is usually an incidental CT finding, detected in approximately 2-3% of asymptomatic population. Appears on CT as a high-density (100-600 HU), round or oval, well-defined intraluminal structure. Size typically ranges from 5-15 mm, and size >5 mm increases appendicitis risk. On US, seen as a hyperechoic intraluminal structure with acoustic shadowing. On MRI, creates signal void with low signal on all sequences.
Age Range
5-85
Peak Age
35
Gender
Equal
Prevalence
Uncommon
Appendicolith formation begins with accumulation of fecal material in the appendix lumen. The appendix lumen is narrow and long with limited peristaltic activity — this anatomical feature creates susceptibility to fecal retention. Calcium phosphate (Ca3(PO4)2) and calcium carbonate (CaCO3) salts from mucosal secretions precipitate in layers onto the accumulated fecal material — forming a concentric lamellar structure (mechanism similar to gallstone formation). Over time, progressive mineralization increases density and a calcified appendicolith develops. The role of appendicolith in appendicitis pathogenesis is mechanical: appendicolith causes luminal obstruction → intraluminal pressure increases → mucosal barrier disrupts → bacterial translocation → transmural inflammation (appendicitis). Larger appendicoliths (>5 mm) more effectively obstruct the lumen and increase appendicitis risk. Additionally, in the presence of appendicolith, increased intraluminal pressure accelerates wall ischemia, increasing perforation risk 2-3 fold (appendicolith = focal pressure point on wall → pressure necrosis → perforation). The high density (100-600 HU) of appendicolith on CT reflects increased photoelectric absorption from the high atomic number of calcium salts (Ca Z=20). Acoustic shadowing on US results from the calcified structure strongly absorbing sound waves and reducing sound wave transmission behind it.
On non-contrast CT, a round/oval, well-defined calcified structure of 100-600 HU density in the appendix lumen. In the context of appendicitis, it is mechanical evidence of luminal obstruction and indicates increased perforation risk. As an isolated finding, incidental appendicolith diagnosis is made and clinical correlation is recommended.
A round or oval calcified structure of 100-600 HU density is seen in the appendix lumen on non-contrast CT. Density depends on degree of calcification: partially calcified fecaliths 100-300 HU, fully calcified appendicoliths 300-600 HU. Usually shows homogeneous or concentric lamellar density pattern. Size typically ranges 5-15 mm. Location is frequently at the base or middle of the appendix.
Report Sentence
A calcified appendicolith measuring approximately ___ mm at ___ HU is seen within the appendix lumen.
Appendicolith shows no enhancement on contrast-enhanced CT — density remains unchanged across all phases (arterial, portal venous, delayed). This confirms the structure is avascular calcified material. Maintaining the same density on non-contrast and contrast-enhanced series is important in differential diagnosis from viable tissue (tumor, polyp). A minimal low-density halo (mucous secretion) may be seen around the appendicolith.
Report Sentence
The calcified structure in the appendix lumen shows no enhancement, consistent with appendicolith.
On US, appendicolith appears as a hyperechoic intraluminal structure with strong posterior acoustic shadowing in the appendix lumen. Acoustic shadowing reflects the high calcification content of appendicolith and is similar to acoustic shadowing of gallstones. Appendicolith is usually round or oval shaped, 5-15 mm in size. Detected as an immobile structure within the lumen when the appendix is localized using graded compression technique.
Report Sentence
A hyperechoic structure measuring approximately ___ mm with acoustic shadowing is seen in the appendix lumen, consistent with appendicolith.
On MRI, appendicolith appears as an intraluminal structure with low signal (signal void) on all sequences. Hypointense on both T1 and T2-weighted images. Calcifications do not produce signal on MRI because they contain no (or very few) protons — this property creates signal void. Susceptibility artifact (blooming) may be seen on GRE/T2* sequences. MRI has lower sensitivity for appendicolith detection compared to CT and US.
Report Sentence
An intraluminal structure with low signal (signal void) on all MRI sequences is seen in the appendix lumen, consistent with calcified appendicolith.
No vascularity is seen within or around the appendicolith on Doppler US — confirming it as a calcified avascular structure. When appendicitis is present, increased Doppler flow may be seen in the appendiceal wall surrounding the appendicolith, but the appendicolith itself is avascular. Doppler evaluation aids in distinguishing appendicolith from vascular intraluminal pathologies (polyp, tumor).
Report Sentence
No Doppler flow is seen in the hyperechoic structure in the appendix lumen, consistent with avascular appendicolith.
Criteria
Homogeneous high density of 300-600 HU on CT. Complete mineralization of calcium phosphate and carbonate crystals. Produces strong acoustic shadowing on US.
Distinct Features
Easily detected on CT. Diagnostic with classic acoustic shadowing on US. Density unchanged across all phases. Recognized without contrast requirement.
Criteria
Mixed density of 100-300 HU on CT. Scattered calcification foci within fecal matrix. Weak or absent acoustic shadowing on US.
Distinct Features
Detectable on CT but may be missed on US (weak shadow). No enhancement. Heterogeneous internal structure. Intraluminal location supports diagnosis.
Criteria
Soft tissue density (20-80 HU) on CT. No calcification. May cause luminal obstruction but is difficult to detect on imaging.
Distinct Features
May be difficult to distinguish from appendiceal contents on CT. No acoustic shadowing on US. Suspected as intraluminal material within dilated appendix. Best evaluated on non-contrast CT.
Distinguishing Feature
In appendicitis, appendicolith is an accompanying finding with dilated appendix (>6 mm) and fat stranding; in isolated appendicolith, appendix is normal caliber with no inflammatory findings. Clinical context (right lower quadrant pain, fever) is determinant in differential diagnosis.
Distinguishing Feature
Carcinoid tumor appears as enhancing solid nodule (enhancement present); appendicolith shows no enhancement and is calcified. Carcinoid typically at appendix tip; appendicolith usually basal or mid-appendix.
Distinguishing Feature
In appendiceal diverticulitis, focal wall defect and inflammation are prominent; in appendicolith, intraluminal calcified structure is the primary finding with no inflammation (isolated). Both may coexist — appendicolith may trigger diverticulum formation.
Urgency
routineManagement
surveillanceBiopsy
Not NeededFollow-up
no-follow-upIsolated appendicolith (without appendicitis findings) is usually clinically insignificant and requires no urgent treatment. Incidental appendicolith should be reported in the radiology report with recommendation for clinical correlation. If size >5 mm or patient reports right lower quadrant pain, clinical follow-up should be considered for appendicitis risk. When appendicitis is present, appendicolith increases complicated appendicitis (perforation) risk 2-3 fold and should be considered in surgical decision-making. Conservative treatment (antibiotics) has lower success rates in the presence of appendicolith — early surgery should be preferred. Detection of appendicolith on preoperative CT alerts the surgeon to perforation possibility.
Isolated appendicolith (without appendicitis signs) is usually clinically insignificant and requires no treatment. However, appendicoliths >5 mm carry appendicitis risk and clinical correlation is recommended. When accompanied by appendicitis, complicated appendicitis (perforation) risk increases 2-3 fold. Incidental appendicolith should be reported with recommendation for clinical correlation.