Bony Sheathed Chorda Tympani

Endoscopic Anatomy of the Chorda Tympani: Systematic Dissection, Novel Anatomic Classification, and Surgical Implications

HYPOTHESIS

A transcanal endoscopic approach enables visualization of the variable course of the chorda tympani inside the middle ear.

BACKGROUND

The chorda tympani is the longest intrapetrous branch of the facial nerve. Despite having been investigated in several studies, a description of its tympanic tract from an endoscopic point of view is lacking in the literature.

METHODS

We performed transcanal endoscopic dissections of 44 human cadaveric head and ear specimens. The entry point of the chorda tympani into the middle ear was classified into four categories according to its location, and as covered or dehiscent according to its appearance. The chordal eminence (CE) was defined as absent, shallow, intermediate, prominent, or fused, based on its shape and extension. The relationship of the chorda tympani to adjacent bony and ligamental structures was assessed.

RESULTS

The tympanic tract of the chorda tympani was divided into three portions. The periannular segment was dehiscent in 54.5% of specimens, with type II being the most frequent entry point configuration (52.3%). In the interossicular segment, the nerve consistently passed lateral to the incus and medial to the malleus. The course of the intrapetrous segment was independent from the conformation of the tensor fold and supratubal recess.

CONCLUSION

The transcanal endoscopic approach allows a detailed description of tympanic segment of the chorda tympani. Novel anatomic classifications of the chorda tympani and CE are proposed herein to highlight their possible surgical implications during otologic procedures.

Congenital Familial Fixation of the Malleus

We present a familial association of radiographically and surgically demonstrated mallear fixation with concurrent stapedial abnormality and dehiscence of the facial nerve in a father and son, including history, physical findings, surgical findings, radiologic analyses, and a literature review. A 12-year-old boy presented with long-term left-sided conductive hearing loss, and was found to have mallear fixation and a dehiscent facial nerve on a computed tomographic (CT) scan of the temporal bone. Release of the malleus was performed at surgery, revealing hypermobility of the remaining ossicular chain. A repeat CT scan of the temporal bone showed successful release of the mallear head. The patient's father later presented with bilateral hearing loss, and a CT scan of the temporal bones showed bilateral osseous fixation of the mallear head to the tegmen and bilateral facial nerve dehiscences. He underwent right middle ear exploration, but release of the malleus was not performed because of the risk to the dehiscent facial nerve. The stapes crurae were found to be filiform at surgery. This is the first reported familial association of mallear fixation. Mallear fixation with facial nerve dehiscence and an abnormal stapes occurring in a parent and his child is interesting embryologically, and suggests that these anomalies may be genetically linked.

Clinical anatomy of the chorda tympani: a systematic review

OBJECTIVE

The chorda tympani is at risk of iatrogenic injury throughout its course. This paper reviews the clinical anatomy of the nerve in adults.

DESIGN

Systematic literature review.

METHOD

Relevant English-language articles were identified using five electronic databases and one search engine. Data from approximately 70 scientific papers were supplemented with information from selected reference texts.

RESULTS

The anatomy of the chorda tympani differs from standard descriptions, particularly regarding its exit from the middle ear and area of lingual innervation. Whilst it is known to convey taste sensation from the anterior two-thirds of the tongue and parasympathetic innervation to the submandibular and sublingual salivary glands, the chorda tympani probably has additional sensory and secretomotor functions.

CONCLUSION

A detailed understanding of the anatomy of the chorda tympani may help to reduce the risk of iatrogenic injury during head, neck and middle-ear surgery, and to explain the variable consequences of such injury.