The Functions of the Nervus Intermedius

Letters to the Editor Letters to the Editor

Published ahead of print on June 30, 2011
doi: 10.3174/ajnr.A2624

American Journal of Neuroradiology 32:E144, August 2011
© 2011 American Society of Neuroradiology

A. Alfieria, J. Fleischhammera and J. Prella
aMartin Luther University 
Halle-Wittenberg, Germany

We read with extreme interest the article written by Burmeister et al entitled “Identification of the Nervus Intermedius Using 3T MR Imaging.”1 It is surprising that this minute nerve has gained such a wide clinical, functional, and now radiologic interest since the original description in 1778 by Wrisberg.2

However, there is a point of concern in the article. The authors stated in the introduction that one of the functions of the nervus intermedius (NI) is the “sensory and parasympathetic innervation of the parotid gland.” This sentence is somewhat troubling, and we cannot agree with it.

To our knowledge, the NI innervates the lacrimal, submandibular, and sublingual glands. The afferent component of the NI carries sensorial perception from the skin of the external auditory meatus and from the nasopharynx and nose; and taste from the anterior two- thirds of the tongue, floor of the mouth, and the palate.3 Moreover, contemporary intraoperative electrophysiologic observations have shown an unforeseen electromyographic activity of perioral muscles after NI stimulus,4,5 which can help in the operative recognition of the nerve and may involve the presence of a small amount of motor fibers.

On the other hand, it is generally accepted that the parasympathetic innervation of the parotid gland originates in the inferior salivary nucleus, leaving the brain stem through the tympanic nerve, a branch of the ninth cranial nerve. From then on, the fibers convey into the lesser petrosal nerve entering the oticganglion. The parotid gland is, thereafter, reached through the auriculotemporal nerve, a subdivision of the mandibular subdivision of the trigeminal nerve.6

In conclusion, we could not find any suggestion that the NI innervates the parotid gland directly.

References

  1. Burmeister HP, Baltzer PA, Dietzel M, et al. Identification of the nervus intermedius using 3T MR imaging. AJNR Am J Neuroradiol 2011;32:460–64. Epub 2011 Feb 3[Abstract/Free Full Text]
  2. Alfieri A, Strauss C, Prell J, et al. History of the nervus intermedius of Wrisberg. Ann Anat 2010;192:139–44[CrossRef][Medline]
  3. Gacek R, Lyon MJ. Evidence of a gustatory-vestibular pathway for protein transport. Otol Neurotol 2010;31:313–18[CrossRef][Medline]
  4. Scheller C, Rachinger J, Prell J, et al. Schwannoma of the intermediate nerve. J Neurosurg 2008;109:144–48[CrossRef][Medline]
  5. Ashram YA, Jackler RK, Pitts LH, et al. Intraoperative electrophysiologic identification of the nervus intermedius.Otol Neurotol 2005;26:274–79[CrossRef][Medline]
  6. May M, Shaitkin B. The Facial Nerve. New York: Thieme Medical Publisher; 2000

Reply

Published ahead of print on June 30, 2011
doi: 10.3174/ajnr.A2641

American Journal of Neuroradiology 32:E145, August 2011
© 2011 American Society of Neuroradiology

H. P. Burmeistera
aInstitute of Diagnostic and Interventional Radiology 
University Hospital 
Friedrich Schiller University Jena 
Jena, Germany

We thank Alfieri, Prell, and Fleischhammer for their very careful reading of our work1 and their thoughtful comments.

Before replying to the matter of concern stated by Alfieri and colleagues, we first would like to emphasize that neither is there a causal relationship between our study of identification of the nervus intermedius (NI) by using 3T MR imaging and the question of how the parotid gland is innervated nor are the results of our study negatively influenced or called into question by this concern.

We agree with Alfieri and colleagues that there is no proof so far that the NI in humans directly innervates the parotid gland.

However, to provide an indemnification for this erroneous mention of the parotid gland, we suggest thinking about whether there might be implications for an indirect or even direct innervation because we also agree with Alfieri et al that “not all features are well known and the common definition as a purely sensory and parasympathetic root of the facial nerve may not cover all aspects of the nervus intermedius.”2

Alfieri and colleagues stated that it has been generally accepted that the parasympathetic innervation of the parotid gland originates in the inferior salivary nucleus—as in most mammals. We agree with this general acceptance, though we think that the lack of clarity should be corrected before the glossopharyngeal nerve is claimed to be exclusively responsible for parotid gland innervation in humans.

To the best of our knowledge, the precise location of the inferior salivatory nucleus (separated from the superior salivatory nucleus) in adult humans has not yet been identified.3 Therefore, regarding the efferent innervation, future research should evaluate to what extent the inferior (nervus glossopharyngeus) and superior salivary neurons (NI) intermingle, interact, or even form a common or inhomogeneous salivary area as was found in the rat.4

Furthermore, a secretory role for the facial nerve was described in other mammals such as the rat.5 In addition, Porto et al6reported on failures of Jacobson’s nerve resection to eliminate parotid secretion in clinical cases. That finding suggests thatan alternative secretory route to the parotid gland exists. They state that only the facial nerve carries accessory efferent fibers to the gland in the cat.6

In our clinical experience, resection of the glossopharyngeal nerve in humans also does not invariably lead to a completetermination of saliva production in the parotid gland.

Finally, we like to refer to the interconnections of the facial, intermediate, and glossopharyngeal nerves (Figs 2–24, eg, the lesser petrosal nerve) described by May and Schaitkin.7 These interconnections are not conclusively evaluated in humans.

References

  1. Burmeister HP, Baltzer PA, Dietzel M, et al. Identification of the nervus intermedius using 3T MR imaging. AJNR Am J Neuroradiol 2011;32:460–64. Epub 2011 Feb 3[Abstract/Free Full Text]
  2. Alfieri A, Strauss C, Prell J, et al. History of the nervus intermedius of Wrisberg. Ann Anat 2010;192:139–44[CrossRef][Medline]
  3. Gai WP, Blessing WW. Human brainstem preganglionic parasympathetic neurons localized by markers for nitric oxide synthesis. Brain 1996;119(pt 4):1145–52[Abstract/Free Full Text]
  4. Rezek Ö, Boldogkoi Z, Tombácz D, et al. Location of parotid preganglionic neurons in the inferior salivatory nucleus and their relation to the superior salivatory nucleus of rat. Neurosci Lett 2008;440:265–69[CrossRef][Medline]
  5. Khosravani N, Sandberg M, Ekström J. The otic ganglion in rats and its parotid connection: cholinergic pathways, reflex secretion and a secretory role for the facial nerve. Exp Physiol 2006;91:239–47. Epub 2005 Nov 4[Abstract/Free Full Text]
  6. Porto AF, Proud GO, Norris CW, et al. Secretory innervation of the parotid gland. Otolaryngol Head Neck Surg1981;89:16–19[Medline]
  7. May M. Anatomy for the Clinician. In: May M, Schaitkin BM, eds. The Facial Nerve. 2nd ed. New York: Thieme; 2000:19–56
The Functions of the Nervus Intermedius