Suspect Appendicitis | The Common Vein

Suspect Appendicitis – Imaging Strategy

Author: Charles Allison, MB ChB

Editor Ashley Davidoff MD

CLINICAL BACKGROUND–

Appendicitis classically presents with abdominal pain that starts at the umbilicus and and migrates to the right lower quadrant and may be associated with systemic symptoms and signs such as nausea, vomiting, fever. The pain almost always precedes the vomiting. On examination there is usually tenderness with guarding and rebound in the right lower quadrant at Mc Burney’s point, and rectal examination usually reveals right sided pelvic tenderness. Systemically mild dehydration, fever and an elevated wcc are associated signs. (Family Practice Notebook). The classical pain only occurs in about 50% of patients. When the patients presents with these classical features there is no reason to go any further with imaging to confirm the diagnosis. However appendicitis is notoriously a masquerader from being relatively asymptomatic

IMAGING STRATEGIES

WHAT STUDY?

When the patient presents with classical symptoms and signs no imaging indicated. In the patient who does not presents with classical signs he two studies to consider are ultrasound and CTscan. Plain film of the abdomen may show indirect signs of appendicitis such as an appendicolith, or an ileus, but is not any more helpful in the diagnosis than the clinical examination.

The overall accuracy of US for appendicitis is reported at 70-95% and for CT accuracy is 93-98%.

In the young female who is thin and in whom pain related to ovulation is a clinical consideration, US is the study of choice.

In thin young males US is also the study of choice.

In pregnancy, in the first and second trimester US is the study of choice while in the third trimester aMRI with gadolinium is the study of choice. (Birchard, Cobben,)

In the rest of the patients CTscan with oral and i/v contrast is the study of choice.

WHY?

In those patients who are in their in reproductive age, the safest study to perform is an US. The study is operator dependant, and patient dependant. The appendix may be retrocecal and gas and soft tissues between the transducer and the appendix may limit the study. On the other hand a hemorrhagic cyst, torsion and an ectopic pregnancy are in the differential diagnosis in a young female and US is the study of choice to evaluate for these latter considerations.

In the third trimester of pregnancy the gravid uterus shifts the appendix and it therefore cannot be easily identified. CT carries the risk of radition to the fetus and MRI has been shown to be accurate in these circumstances. (Birchard, Cobben,)

In larger patients and the elderly, the greater accuracy of CT makes it the study of choice. The presence of intraabdominal fat allows the associated periappendiceal changes to be identified. On the other hand in patients with little intraabdominal fat it is sometimes difficult to identify the appendix with CT. A perforated appendix is quite obvious on CT scan.

BACKGROUND TO THE DISEASE:

Acute appendicitis is the most common surgical emergency in the Western World. It typically affects teenagers and young adults, though may occur in younger children and infants. There is a smaller secondary peak in the elderly. It is caused by infection superimposed on any from of obstruction of the vermiform appendix. This obstruction is most commonly secondary to fecoliths or lymphoid hyperplasia (from viral infection, for example). Diagnosis is made on clinical history and examination in combination with raised biochemical markers of inflammation (white cell count, C-reactive protein).

WHEN?

There USscan of the RLQ should be performed as soon as possible on the day of presentation. It does not require any patient preparation and most institutions allow these patients to be triaged directly to the US department without a review of the radiologist. CT scan on the other hand requires the patient to be NPO with a 2 hour oral preparation of contrast though some institutions use rectal contrast effectively to avoid the 2 hour wait. When possible intravenous contrast is used.

HOW TO ORDER?

When ordering an ultrasound for appendicitis it is important to reference the symptom or the sign as the clinical indication and not the diagnosis.

ie Patient with “RLQ pain” is acceptable

Patient with R/O appendicitis is not acceptable.

Patient with “RLQ pain, R/O appendicitis ” is optimal

The examination is called a “limited RLQ ultrasound”

PATIENT PREPARATION

For the patients who are undergoing US, no preparation is required. The study takes about 30 minutes.

For CT scan the patient is NPO for 4 hours except for the oral prep which is 90% water. Some institutions prefer rectal contrast. Intravenous contrast is used when possible. Once the patient is on the table the study takes less than a minute to perform.

CLINICAL RED FLAGS:

Sudden increase in pain with generalized peritonism and possible shock may indicate perforated of the inflamed appendix and subsequent peritonitis. This requires immediate antibiotic and supportive therapy. Persistent swinging fevers may indicate intra-abdominal abscess, with could be confirmed on abdominal CT with contrast. New RUQ pain may suggest portal thrombophlebitis.

For assistance with imaging strategies email radiologist@thecommonvein.net