Zenker's Diverticulum: The Diagnostic Power of Ultrasound

Dear Editor:

We write regarding the paper titled “Zenker diverticulum presenting as a thyroid nodule” published in a recent issue of Thyroid (1). We congratulate Shanker and Davidov (1) for sharing their experience and would like to make some additional comments.

Zenker's diverticulum (ZD) is due to a muscular dehiscence at the Killian's triangle between the oblique fibers of the inferior constrictor muscle and transverse fibers of the cricopharyngeus muscle (C5–C6 level). It is usually behind the upper left thyroid lobe. ZD most commonly appears between the sixth and ninth decades of life. It is two to three times more frequent in men than women and seldom occurs in Asian people. There is typically dysphagia, as the distended pouch compresses the esophagus, as well as noisy deglutition, regurgitation of undigested food, mild to moderate weight loss, halitosis, and dysphonia. ZD may also be responsible for more severe complications such as aspiration. As the sac enlarges, a ZD may lead to severe problems with nutrition and even complete esophageal obstruction.

Being close to the thyroid gland, ZD can mimic thyroid nodules and recurrent laryngeal lymph nodes in patients who have had surgery for thyroid cancer (2). In fact, postthyroidectomy weakness at the Killian triangle due to upper thyroid lobe removal can facilitate herniation of the diverticulum.

ZD has quasipathognomonic features on neck sonography, which preclude hazardous fine-needle aspiration biopsy or diagnostic cervicotomy (3). There may be transient changes in size and other aspects during rotation of the patient's neck. Performance of water swallowing and compression/decompression maneuvers during ultrasound (US) is helpful in suspecting the diagnosis, which can be confirmed by barium swallow.

Variants of ZD include large diverticuli filled with air producing tail comet artifacts, hyperechoic punctuations, or mixed components giving a thyroid tumor-like aspect to the hernia. Large diverticuli can expand bilaterally behind both thyroid lobes and present decreased probe-related compressibility (Supplementary Fig. S1A, B; Supplementary Data are available online at www.liebertonline.com/thy). Upon suspicion of ZD, the practitioner may thus use probe compression to make the patient regurgitate, listen for “gurgles” (Boyce's sign), and observe subsequent imaging modifications including a “blooming effect.” A color-blooming “artifact” may be seen as gray-scale pixels changing into colored pixels. This is caused by a sudden increase in the air flow signal strength within the “nodule” due to the US probe compression (Supplemental Fig. S1A). Of note, this artifact is never observed in thyroid carcinoma or in a branchial cleft fistula.

Interestingly, a ZD smaller than 10 mm can mimic microcarcinomas of the left posterior thyroid or suspicious hyperechoic recurrent lymph nodes after thyroidectomy (Supplementary Fig. S1C) (2). The possibility of ZD should thus be considered in cases of suspicious “thyroid nodule” or postoperative “node” adjacent to the esophagus even without US change after swallowing. In such cases, the recent development of elastography in the neck (4) may help to decrease the false-positive rate for the diagnosis of a malignant thyroid nodule. The three main types of US elasticity imaging include elastography, which tracks tissue motion during compression to obtain an estimate of strain, sonoelastography, which uses color Doppler to generate an image of tissue motion in response to external vibrations, and tracking of shear wave propagation through tissue to obtain the elastic modulus as shown in one of our patients (Supplementary Fig. S1D). Shear wave propagation actually gives a reproducible quantitative value of constraint in elasticity of both the thyroid (mean, 6.7 kPa) and esophagus (mean, 9.9 kPa) in kilopascals (low value = blue color = benign). Malignant thyroid nodules with microcalcifications have a higher constraint value than a ZD (higher value in kPa = red color). Another entity in the differential diagnosis, which is quite unusual, is a fourth branchial cleft fistula. These patients usually have a history of repetitive neck infections or left-sided thyroiditis and demonstrate a collection posterior to the upper left thyroid lobe with a hypervascular wall with no “blooming artifact” and with a low elasticity value of constraint.

Thus, a ZD can mimic a suspicious thyroid nodule or a malignant neck node in an operated thyroid cancer patient. ZD can be suspected on sonography using color Doppler, “dynamic maneuvers,” and the innovative shear wave elastography with confirmation by barium swallow, thus avoiding fine-needle aspiration biopsy. In general, only symptomatic ZD or enlarging diverticuli are operated on because of the risk of compression and associated malignancy.