The term appendicolith is preferred over the less specific terms, coprolith and fecolith. Approximately 10% of patients with acute appendicitis have a radiographically visible appendicolith. One third of surgically removed appendices, however, contain an appendicolith. The calcification may form around any type of nidus, including a piece of vegetable matter, swallowed foreign body, or even barium. The appendicolith tends to be round or oval, smooth, and laminated (Film .2Z). The size varies, but stones in the l-2 cm range are common with stones up to 4 cm in size having been reported. The location is usually in the right lower quadrant, but the pelvis, right upper quadrant in the case of retrocecal appendix, and even the left upper quadrant may be the site.
The differential diagnosis includes the following:
a) Phlebolith - these rounded calcifications tend to occur in clusters, are usually lower in the pelvis, and frequently contain a central lucency.
b) Calcified lymph node - these tend to be amorphous, irregular, "popcorn" calcifications.
c) Ureteral calcifications - this calcification should conform to the course of the ureter and tends to be smaller and less often laminated.
d) Benign bone island in the iliac wing - this density will not move with changes in position of the patient, maintaining a constant location within the iliac bone.
The presence of an appendicolith is significant clinically since patients with this radiograph finding are more likely to have appendicitis complicated with perforation or abscess. This is especially true in children.
The plain film diagnosis of acute appendicitis in the absence of an appendicolith can be difficult with the plain film demonstrating abnormalities in approximately one half of patients. The following radiographic findings have been described, but no one of these is as helpful as an appendicolith.
1) Abnormal bowel gas pattern. The bowel gas pattern in acute appendicitis can be anywhere from normal to consistent with a complete small bowel obstruction. A local ileus in the right lower quadrant with air fluid levels can be seen. Occasionally fluid-filled right lower quadrant small bowel loops may present as a soft tissue mass. A dilated transverse colon in pediatric patients with a perforated appendix has also been described.
2) Abnormal cecum and ascending colon. Local inflammation and edema may cause thickening of the colon wall and widen the haustra. A cecal air fluid level may be present.
3) Extraluminal soft tissue mass. This finding can be seen in up to one third of patients with perforation. A combination of edema, fluid, and fluid-filled loops of small bowel produce the effect. A mottled gas collection within the soft tissue mass is highly suggestive of an abscess.
4) Obliteration of normal fat planes. Sufficient inflammation from appendicitis may alter the water density of the surrounding fat and obscure the right properitoneal flank stripe, psoas muscle, or obturator muscle.
5) A small amount of free intraperitoneal or retroperitoneal air may rarely be present.
The use of the barium enema, ultrasound, and CT in diagnosing acute appendicitis will be discussed in a separate section.