Excision of Greater Superficial Petrosal Nerve Schwannoma Via a Pure Endoscopic Endonasal Approach

Greater superficial petrosal nerve (GSPN) schwannomas are an exceedingly rare nerve sheath tumor. The current literature search was conducted using Medline and Embase database by key search terms. Only 31 cases have been reported in the literature so far. Facial palsy, hearing loss, and xerophthalmia accounted for 48.4% (15), 41.9% (13), and 29% (9) of all cases, respectively. The middle cranial fossa approach was used in all previous reports. A retrospective review of 2 GSPN schwannomas patients treated by endoscopic endonasal approach (EEA) in our center was collected. Clinical records, including clinical features, pre- and postoperative images, surgery, and follow-up information, were reviewed. In all cases, clinical features including facial numbness and headache were found, with tinnitus in case 1, hearing loss, xerophthalmia in case 2. Imaging studies showed a solid mass that originated in the anterior of the petrous bone. Two patients were treated by EEA. Furthermore, no recurrence was found during the follow-up period (15-29 months) in both of the 2 cases after the operation. Complete resection of GSPN schwannomas can be achieved via the pure EEA. Endoscopic endonasal approach for radical removal of tumors is safe and feasible.

Comprehensive microsurgical anatomy of the middle cranial fossa: Part II-neurovascular anatomy

In order to master the surgical approaches to the middle cranial fossa, the surgeon needs to understand the relevant bony anatomy. However, she/he also needs to have a clear and sound understanding of the neural and vascular anatomy because, oftentimes, the osseous anatomy (except for the optic apparatus) should be removed to expose and protect the neurovascular anatomy. This is the second of a two-part article discussing the neurovascular anatomy of the middle cranial fossa. A brief discussion of the surgical approaches follows.

Regenerative Failure Following Rat Neonatal Chorda Tympani Transection is Associated with Geniculate Ganglion Cell Loss and Terminal Field Plasticity in the Nucleus of the Solitary Tract

Neural insult during development results in recovery outcomes that vary dependent upon the system under investigation. Nerve regeneration does not occur if the rat gustatory chorda tympani nerve is sectioned (CTX) during neonatal (≤P10) development. It is unclear how chorda tympani soma and terminal fields are affected after neonatal CTX. The current study determined the impact of neonatal CTX on chorda tympani neurons and brainstem gustatory terminal fields. To assess terminal field volume in the nucleus of the solitary tract (NTS), rats received CTX at P5 or P10 followed by chorda tympani label, or glossopharyngeal (GL) and greater superficial petrosal (GSP) label as adults. In another group of animals, terminal field volumes and numbers of chorda tympani neurons in the geniculate ganglion (GG) were determined by labeling the chorda tympani with DiI at the time of CTX in neonatal (P5) and adult (P50) rats. There was a greater loss of chorda tympani neurons following P5 CTX compared to adult denervation. Chorda tympani terminal field volume was dramatically reduced 50 days after P5 or P10 CTX. Lack of nerve regeneration after neonatal CTX is not caused by ganglion cell death alone, as approximately 30% of chorda tympani neurons survived into adulthood. Although the total field volume of intact gustatory nerves was not altered, the GSP volume and GSP-GL overlap increased in the dorsal NTS after CTX at P5, but not P10, demonstrating age-dependent plasticity. Our findings indicate that the developing gustatory system is highly plastic and simultaneously vulnerable to injury.

Microsurgical localization of the cochlea in the extended middle fossa approach

Objective In the extended middle fossa approach, a portion of the petrous bone known as Kawase's rhomboid can be drilled to expose the posterior fossa through a middle fossa corridor. During this bony resection, the cochlea is placed at risk. The objective of this study was to objectively detail the position of the cochlea in relation to reliable surgical landmarks. Methods Eleven cadaveric specimens were dissected-including six cadaveric heads and five dry temporal bones by means of an anterior petrosectomy with skeletonization of the cochlea. Three anatomic measurements describing the location of the cochlea in relation to the extrapolated intersection of the greater superficial petrosal nerve (GSPN) and facial nerve were recorded. These measurements were then correlated with thin-cut temporal bone computed tomography scans from 25 patients with morphologically normal inner ears. Results In the cadaveric specimens, the anterior border of the membranous basal turn of the cochlea was located an average of 7.56 mm (6.4 to 8.9 mm) anterior to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the GSPN. The medial border of the membranous cochlea (medial margin of basal turn) was located an average of 8.2 mm (6.9 to 8.9 mm) medial to the extrapolated junction of the GSPN and facial nerve, as measured along the course of the facial nerve. The average maximum distance from the extrapolated junction of the GSPN and facial nerve to the membranous cochlea was 9.3 mm (8.2 to 10.3 mm). These anatomic measurements correlated well with radiologic measurements of the same parameters. Conclusion When drilling Kawase's rhomboid, it is useful to locate the extrapolated junction of the GSPN and the facial nerve. Drilling of the anteromedial petrous bone outside of a radius of 12.5 mm from the extrapolated junction of GSPN and facial nerve appears to be associated with a low degree of risk to the cochlear apparatus.

Clinical functional anatomy of the pterygopalatine ganglion, cephalgia and related dysautonomias: A review

The purpose of this article is to explain the anatomy of the pterygopalatine ganglion (PPG), its location in the pterygopalatine fossa (PPF) in the skull, and the relationship it has to the Vidian nerve terminal branches and the fifth cranial nerve. An overview of the neuro-anatomical/clinical correlations, a spectrum of pathologies affecting the seventh cranial nerve and some therapies both medical and surgical are noted. The focus is the pterygopalatine region with discussion of the proximal courses of the seventh and fifth cranial nerves and their pathological processes. The ganglion is used as an example of neuro-anatomical model for explaining cluster headaches (CH). Radiological correlation is included to clarify the location of the PPF and its clinical importance.

Each sensory nerve arising from the geniculate ganglion expresses a unique fingerprint of neurotrophin and neurotrophin receptor genes

Neurons in the geniculate ganglion, like those in other sensory ganglia, are dependent on neurotrophins for survival. Most geniculate ganglion neurons innervate taste buds in two regions of the tongue and two regions of the palate; the rest are cutaneous nerves to the skin of the ear. We investigated the expression of four neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and NT-4, and five neurotrophin receptors, trkA, trkB, trkC, p75, and truncated trkB (Trn-B) in single sensory neurons of the adult rat geniculate ganglion associated with the five innervation fields. For fungiform papillae, a glass pipette containing biotinylated dextran was placed over the target papilla and the tracer was iontophoresed into the target papilla. For the other target fields, Fluoro-Gold was microinjected. After 3 days, geniculate ganglia were harvested, sectioned, and treated histochemically (for biotinylated dextran) or immunohistochemically (for Fluoro-Gold) to reveal the neurons containing the tracer. Single labeled neurons were harvested from the slides and subjected to RNA amplification and RT-PCR to reveal the neurotrophin or neurotrophin receptor genes that were expressed. Neurons projecting from the geniculate ganglion to each of the five target fields had a unique expression profile of neurotrophin and neurotrophic receptor genes. Several individual neurons expressed more than one neurotrophin receptor or more than one neurotrophin gene. Although BDNF is significantly expressed in taste buds, its primary high affinity receptor, trkB, was not prominently expressed in the neurons. The results are consistent with the interpretation that at least some, perhaps most, of the trophic influence on the sensory neurons is derived from the neuronal somata, and the trophic effect is paracrine or autocrine, rather than target derived. The BDNF in the taste bud may also act in a paracrine or autocrine manner on the trkB expressed in taste buds, as shown by others.

Behavioral discrimination between quinine and KCl is dependent on input from the seventh cranial nerve: implications for the functional roles of the gustatory nerves in rats

The rat glossopharyngeal nerve (GL), which innervates posterior tongue taste buds, contains several physiologically defined taste fiber types; at least one type is primarily responsive to certain alkaloids (such as quinine), and another is primarily responsive to acids and salts. In contrast, the chorda tympani (CT), which innervates anterior tongue taste buds, does not appear to contain fibers that differentially respond to quinine relative to salts and acids. It was therefore predicted that GL transection should disrupt behavioral discriminations between quinine and either acids or salts. Water-restricted rats were trained to press one of two levers if a sampled taste stimulus was quinine (0.1-1.0 mM) and the second lever if the sampled stimulus was KCl (0.1-1.0 M). Sham surgery, GL transection, and sublingual and submaxillary salivary gland extirpation were found to have no effect relative to presurgical performance. Both CT transection and combined GL and CT transection caused a substantial and approximately equal decrement in discrimination performance. Removal of the gustatory branches of the seventh cranial nerve [CT and greater superficial petrosal (GSP)] nearly eliminated the discrimination of the taste stimuli, and combined transection of the CT, GL, and GSP unequivocally reduced performance to chance levels. Although these findings were not presaged by the known electrophysiology, they nonetheless compare favorably with other studies reporting little effect of GL transection on behavioral responses to quinine. These results, in the context of other discrimination studies reported in the literature, suggest that, in rats, the neural coding of taste quality depends primarily on the input of the facial nerve.