Sonography is widely available, can be performed at the bedside, involves a short acquisition time, does not use ionizing radiation, is relatively inexpensive, and may show evidence of other causes of abdominal pain. It is particularly useful in evaluating young women, in whom the radiation dose to the reproductive organs should be minimized and for whom it is important to exclude ovarian and uterine conditions that might mimic appendicitis. There have been multiple studies evaluating the value of sonography in the evaluation of appendicitis, showing varying sensitivity, specificity, and accuracy. However, a recent study by Pacharn et al found that sonography for acute appendicitis had a negative predictive value of 95%, making it an excellent screening tool in the evaluation of acute appendicitis. Goldin et al suggested that standardizing the technique and criteria will decrease variability in the diagnostic accuracy of sonography across institutions.
The standard sonographic evaluation of the abdomen based on the American Institute of Ultrasound in Medicine practice guideline includes imaging of the appendix. A complete abdominal sonographic examination does not need to be performed in the evaluation of acute appendicitis.
However, because the appendix is not always located in the right lower quadrant and an abscess could be present, imaging should include not only the right lower quadrant but also the pelvis and left lower quadrant. A survey of the abdomen for free fluid or bowel thickening elsewhere is also helpful, especially in cases of suspected perforation.
At the start of the examination, it is helpful to ask the patient to point to the site of maximal tenderness and begin scanning in this location. Using a high-resolution linear transducer, the abdomen should be compressed while scanning, which moves bowel gas out of the field of view. This compression sonography is performed with an empty bladder. The most reliable way to identify the appendix is to find the ascending colon, follow the colon proximally to the cecum, and then find the appendix extending off the cecum.
If the appendix cannot be seen in the supine position, it may be helpful to place the patient in the left lateral decubitus position to cause a retrocecal appendix to be better seen.
Scanning with a full bladder may also be helpful because it can better delineate a deep pelvic appendix that might be obscured by overlying bowel.
The complete appendix should be visualized, including the tip. The maximal outer wall diameter should be measured, and the wall thickness should be measured along the course of the appendix. The normal maximal outer wall diameter of the appendix is less than 6 mm, and the mural thickness is less than 2 mm (Figure 1A). Compression of the appendix should be performed, with documentation of the appearance of the appendix during compression. A normal appendix compresses (Figure 1B). Secondary signs such as free fluid, a fecalith, and hyperechoic surrounding fat should be documented. Doppler imaging is helpful to evaluate for hyperemia; however, a necrotic appendix will have decreased or no blood flow. Video clips should be obtained to show normal peristalsis unless the physician is present during the scan. If an abscess is suspected, a lower- frequency curved array transducer may be used for a larger field of view and deeper penetration.
It is not always necessary to identify a normal appendix to consider the findings negative. If there are no secondary signs as mentioned above, and clinical suspicion is moderately low for appendicitis, many institutions stop the evaluation and consider the sonographic findings negative for appendicitis.
In the setting of acute appendicitis, the appendix is noncompressible, and the maximal outer wall diameter is greater than 6 mm (Figure 2). An appendicolith may be present, helping the diagnosis (Figure 3); however, an appendicolith can be present without acute appendicitis, and the presence of an appendicolith does not confirm acute appendicitis.
There may also be secondary signs of inflammation, such as hyperechoic surrounding fat, free fluid, or an abscess (Figure 4). The wall may be hyperemic (Figure 5). Enlarged nodes can also be seen in the right lower quadrant, but this finding is nonspecific and can also be seen in patients without appendicitis. The surrounding bowel may be dilated with loss of normal peristalsis due to ileus.
Right lower quadrant sonography, when performed using rigorous technique and criteria for diagnosis, is an excellent screening tool for acute appendicitis. This examination is quick and painless and does not involve the use of ionizing radiation. Although the sensitivity, specificity, and accuracy of sonography vary greatly in studies evaluating the imaging diagnosis of acute appendicitis, it should be the first imaging modality when there is clinical concern for acute appendicitis. Only if the examination is equivocal or if the appendix cannot be identified should other imaging modalities such as CT be considered.
J Ultrasound Med 2012; 31:1153–1157 | 0278-4297 |www.aium.org
Valve of Gerlach/appendiceal orifice Joseph von Gerlach Joseph von Gerlach (1820-1896)J Ultrasound Med 2012; 31:1153–1157 | 0278-4297 |www.aium.org
Appendiceal orifice (arrow) and water filled cecum.
Joseph von Gerlach (April 3, 1820 – December 17, 1896) was a German professor of anatomy at the University of Erlangen. He was a native of Mainz, Rhineland-Palatinate. Gerlach was a pioneer of histological staining and anatomical micrography. In 1858 Gerlach introduced carmine mixed with gelatin as an histological stain.[1] Along with Camillo Golgi, he was a major proponent of the theory that the brain's nervous system consisted of processes of contiguous cells fused to create a massive meshed network. Gerlach summed up his theory by stating: the finest divisions of the protoplasmic processes ultimately take part in the formation of the fine nerve fibre network which I consider to be an essential constituent of the gray matter of the spinal cord. The divisions are none other than the beginnings of this nerve fibre net. The cells of the gray matter are therefore doubly connected by means the nerve process which becomes the axis fibre and through the finest branches of the protoplasmic processes which become a part of the fine nerve fibre net of the gray matter. The reticular theory predominated until the 1890s when Ramon y Cajal brought forth his neuron doctrine of synaptic junctions, which in essence replaced the reticular theory. Gerlach was one of the first physicians to use photomicrography for medical research. In 1863 he published a handbook titled Die Photographie als Hilfsmittel mikroskopischer Forschung (Engl. "Photography as a tool in microscopic science") in which he discusses the practical and technological aspects of microscopic photography. The eponymous "Gerlach's valve" (valvula processus vermiformis) is named after him. This anatomical structure is a fold of membrane sometimes found at the opening of the vermiform appendix.[2] In his article Ueber das Hautathmen[3] (Engl. "On skin respiration") he was the first to show that human skin uses oxygen from ambient air.
