Exoscope-assisted submandibular salivary stones surgery

5.1

Historical background

Salivary stones were extracted as far as before Renascence, as well as abscesses and ranulas. With corpse dissection from the mid-17th century, the increasing anatomic and functional knowledge allowed to broaden surgical techniques. In 1656, Thomas Wharton was the first to describe the submandibular duct, in his paper “Adenographia,” in which he described also the anatomy and function of salivary glands. In the same years, Marcello Malpighi used pioneer microscopes to better understand salivary glands anatomy, with a structured point of view.

Concerning surgical tools and magnification, the microscope was used rarely and mostly for research and anatomical dissection purpose. From the late 19th century, surgical loupes were the main tool used by some surgeons to increase the magnification in this type of surgery.

Although surgical techniques have evolved over time, until 30 years ago, the main approach of Wharton's duct and oral pelvis surgery remained open transoral surgery. From the 1990s, there was an increasing attention to ductal lithiasis, with the development of minimally invasive and nonsurgical techniques of diagnosing and treating salivary gland duct stones, that evolved rapidly, in parallel to conventional surgery. Various combinations of diagnostic and treatment modalities were tried, such as endoscopes and dedicated endoscopic instruments, laser lithotriptors, and intra- or extracorporeal lithotripsy, with a proof of efficacy in most cases of ductal stones.

In 1991, Katz published his early experience with a 0.8-mm mini-endoscope, revealing the endoscopic anatomy of the Wharton's duct. Later, in 1993, Katz and Koningsberger ^, reported independently their successful experience with endoscopic treatment of lithiasis.

Since then, enhanced optical resolution and miniaturization of instruments have resulted in the modern techniques of sialendoscopy. This modality provided a new tool to the surgeon, in addition to the removal of the entire salivary gland and to the marsupialization of the duct and removal of the stone.

In 2015, Razavi et al. described the robot-assisted sialolithotomy with sialendoscopy (RASS) for the management of large palpable hilar submandibular gland stones, as a safe and successful procedure, without damage to the lingual nerve.

The usefulness of 3D technology in improving surgical performance and accuracy was demonstrated in a recent 2019 study by Capaccio et al. describing the removal of submandibular stones with video-assisted transoral technique using 3D-HD sialendoscopy. Recently, exoscope-assisted transoral removal of distal stone of the Wharton's duct was illustrated by our group.

5.2

Introduction

Sialolithiasis is one of the most common nonneoplastic diseases of the salivary glands, with a 1.2% prevalence in the general population. Submandibular glands account for about 79% of all salivary calculi; among these, 34% are localized in Wharton's duct, 57% in the hilum, and 9% inside the gland. When the calculus blocks the salivary flow, symptoms may arise; swelling and pain of the submandibular gland, especially during mealtimes, or foreign body sensation in the floor of the mouth are the commonest reported. Beyond history taking and gland and mouth floor palpation, the main diagnostic tools are ultrasound scan or CT scan without contrast enhancement or diagnostic sialendoscopy. The first treatment indication can include the stimulation of the saliva production and the massage of the gland, to help getting smaller calculi to pass through the papilla. If calculi do not get removed spontaneously, the management is usually the surgical removal of the stone. Different approaches are available such as transoral removal of the calculi, sialoendoscopy, combined approach, or submandibular gland excision.

5.3

Principles

The well-known sialendoscope are semiflexible miniature endoscopes 0°, with integrated irrigatione and working channels, that guarantee adequate maneuverability through the delicate salivary ductal system and enable the minimally invasive removal of obstructions in the salivary ducts.

Although the sialendoscope has brought a paradigm shift in the management of parotid duct stones, especially on small stones, allowing direct removal of stone without risk on the facial nerve, Wharton's duct stones can be considered more challenging for many reasons.

The position of Wharton's duct punctum is quite variable, and it is not always easy to identify without any magnification. Surgical loupes are useful as they provide a good magnification for this anatomical site and they do not interfere with the surgical working space, but they affect just the view of the first surgeon.

Position and dimension of the stone are other factors that have to be taken into account. The majority of submandibular stones are hilar/anterior and result in difficulty to manage with sialendoscope alone, often requiring an intraoral incision for their removal. Sialoliths more than 3.5–4 mm are difficult to manage with a sialendoscope; they can either be broken down with extracorporeal shockwave lithotripsy or with laser fiber passed through the scope (intracorporeal lithotripsy), alternatively these larger stones can benefit from a combined approach (sialendoscope guided external approach). For these manifold reasons, submandibular stone surgery can have a huge benefit from 3D exoscope; this innovative high definition rigid rod lens telescope can be suspended above the surgical field coming from the head of the patients and it produces high-quality full-HD three-dimensional images that can be visualized on a large-format HD 4K resolution flat screen by the surgeon and the other operating room personnel wearing 3D glasses. These features allow a shared high-detailed magnification that well assists the transoral removal of calculi.

The video tower system is the same as the sialendoscope, allowing fast and easy interchangeability between the two tools in combined procedures.