appendicitis
Meaning of appendicitis: An obstructed appendix becomes a closed space under rising pressure, which is what makes the illness progress rather than settle.
Definition of appendicitis
Appendicitis is inflammation of the appendix, the narrow blind-ended tube attached to the first part of the large bowel. It usually begins when the opening of the appendix becomes blocked, so secretions accumulate inside, pressure rises, and the wall becomes inflamed and then infected. Pain characteristically starts vaguely around the navel and later settles at a fixed point in the lower right abdomen.
Why does the pain move?
The appendix hangs from the first part of the large bowel, usually low on the right side. Early on, the inflamed organ signals through nerves serving the gut in general, and those nerves cannot report position, so discomfort is felt vaguely around the navel alongside nausea and loss of appetite. As inflammation reaches the outer surface of the appendix, it irritates the lining of the abdominal wall beside it. That lining is richly supplied with nerves that do report position, so the pain sharpens and shifts to a fixed point over the appendix itself. This migration is one of the most useful features of the illness.
Why does it progress rather than settle?
The appendix becomes a closed space. Its opening blocks, most often with a hardened pellet of stool and sometimes with swollen lymphoid tissue in the wall, while secretion continues into a cavity with no outlet. Pressure rises inside, halting first the drainage of lymph, then venous blood, then the arterial supply to the wall. Tissue starved of blood dies, and dead wall can split open. Bowel contents and pus then enter the abdominal cavity, producing peritonitis, inflammation of the membrane lining the abdomen, which spreads illness through the whole body. That sequence is why the condition is handled as a surgical emergency and why appendectomy remains among the commonest urgent operations. How quickly the sequence runs varies between people and cannot be judged from the severity of the pain.
What produces a similar picture?
| Condition | What differs |
|---|---|
| Mesenteric adenitis | Inflamed abdominal glands after a viral illness, mainly in children |
| Ovarian cyst or twisted ovary | Abrupt onset, pain lower and more central |
| Pregnancy outside the womb | Missed period, faintness, vaginal bleeding |
| Urinary stone | Pain in waves toward the groin, blood in the urine |
| Crohn disease of the last small bowel | Longer history, diarrhea, weight loss |
The overlap is wide enough that a proportion of appendices removed for suspected appendicitis prove normal, and imaging is used to narrow the field. Presentation is least typical at the extremes of age and during pregnancy, when the enlarging womb displaces the appendix upward.
Also known as
Used in a sentence
The child underwent surgery for acute appendicitis with localized peritonitis.
Good to know
The inflamed appendix can perforate as pressure rises within it, and pain that eases briefly before becoming widespread can reflect that rupture rather than recovery. Presentation is frequently atypical in young children, older adults and pregnancy, where the appendix may lie in an unusual position.
Word origin
Where “appendicitis” comes from
From the Latin appendix, an appendage, from appendere, to hang upon, with the Greek suffix -itis for inflammation.