Plunging Ranulas and Prevalence of the "Tail Sign" in 126 Consecutive Cases

Plunging (or diving) ranulas are extravasation pseudocysts arising from the sublingual gland that present as soft submandibular swelling. The "tail sign" has been widely reported as pathognomonic for their diagnosis. It is described as a smooth tapering comet-shaped unilocular fluid mass with its "tail" in the collapsed sublingual space (SLS) and its "head" in the posterior submandibular space. This sign is based on the premise that extravasated saliva from the sublingual gland in the SLS escapes and plunges, over the posterior edge of the mylohyoid muscle into the submandibular space. Therefore, some fluid must be present in the posterior SLS in almost all patients with plunging ranulas. This study aimed to determine the frequency of fluid seen with ultrasound (US) in the posterior SLS to corroborate the tail sign.

A total of 126 consecutive cases of surgically proven plunging ranulas were investigated with US over 13 years. The findings were reviewed retrospectively for the prevalence of fluid in the posterior SLS.

Thirteen patients (10.3%) showed SLS fluid on US images. Most showed fluid extension through a mylohyoid dehiscence. Only 2 patients (1.6%) showed fluid within the posterior SLS, and 1 patient alone in this entire study showed all of the components of the classically described tail sign.

This largest ever radiologic study showed low prevalence of the tail sign in 2 of 126 patients. A mylohyoid dehiscence was the more common route for extravasation. Absence of the tail sign does not exclude the diagnosis of a plunging ranula.