Greater Petrosal Nerve Research Articles

Neural Pathway of Taste & Its Pathological Conditions

Nerves like chorda tympani, greater petrosal nerve (facial nerve branch) glossopharyngeal and vagus take part in the taste sensation and innervate the tongue, palate and epiglottis. The neural pathway of taste is presented in detail in physiological and pathological conditions.

Variants of the Anterior Subtemporal Approach to the Gasserian Ganglion and Related Structures: An Anatomical Study With Relevant Implications for Keyhole Surgery

The advantages and limitations of different craniotomy positions and approach trajectories to the gasserian ganglion (GG) and related structures using an anterior subtemporal approach have not been studied systematically. Knowledge of these features is of importance when planning keyhole anterior subtemporal (kAST) approaches to the GG to optimize access and minimize risks. Eight formalin-fixed heads were used bilaterally to assess temporal lobe retraction (TLR), trigeminal exposure, and relevant anatomical aspects of extra- and transdural classic anterior subtemporal (CLAST) approaches compared with slightly dorsally and ventrally allocated corridors. TLR to the GG and foramen ovale was found to be lower via the CLAST approach (P < 0.001). Using the ventral variant, TLR to access the foramen rotundum was minimized (P < 0.001). The overall TLR was maximal using the dorsal variant (P < 0.001) owing to interposition of the arcuate eminence. An extradural CLAST approach required wide exposure of the greater petrosal nerve (GPN) and middle meningeal artery (MMA) sacrifice. Both maneuvers were spared using a transdural approach. Using CLAST, medial dissection >39 mm can enter the Parkinson triangle, jeopardizing the intracavernous internal carotid artery. The ventral variant enabled access to the anterior portion of the GG and foramen ovale without the need for MMA sacrifice or GPN dissection. The CLAST approach provides high versatility to approach the trigeminal plexus, minimizing TLR. However, an extradural approach jeopardizes the GPN and requires MMA sacrifice. The risk of cavernous sinus violation exists when progressing medially beyond 4 cm. The ventral variant has some advantages to access the ventral structures and avoid MMA and GPN manipulation. In contrast, the usefulness of the dorsal variant is rather limited owing to the greater TLR required.

The modified method of locating related bony structures in intradural anterior transpetrosal approach

Objective To explore the improved method of precisely locating related bony structures in intradural anterior transpetrosal approach. Methods On the 10 dry skulls, the highest point of arcuate eminence (A), the petrous apex (P), the most lateral point of groove for the greater petrosal nerve (B), foramen spinosum (C), foramen ovale (D), trigeminal impression (E) and t foramen lacerum (F)were marked. Using point A as reference point and the line AP as the baseline, the distances of AB, AC, AD, AE and AF and the angles of ∠BAP, ∠CAP, ∠DAP, ∠EAP and ∠FAP were measured. Samples were analyzed by mean and standard deviation, and the data on both sides were compared by t test. Results 1．AB: (11.61±2.31) mm (left), 10.44±2.31 mm (right), t=1.084; AC: (23.14±3.07) mm (left), (21.08±2.67) mm (right), t=1.596; AD: (24.95±2.82) mm (left), (24.38±3.44) mm (right), t=0.408; AE: (18.98±3.11) mm (left), (19.21±3.09) mm (right), t=-0.164; AF: (29.68±2.62) mm (left), (29.25±2.77) mm (right), t=0.725. 2. ∠BAP: (49.15±12.10)° (left), (52.78±14.27)° (right), t=-0.624; ∠CAP: (43.98±6.95)° (left), (48.73±8.02)° (right), t=-1.418; ∠DAP: (38.68±4.81)° (left), (41.48±3.14)° (right), t=-1.543; ∠EAP: (21.93±5.29)° (left), (25.94±6.43)° (right), t=-1.523; ∠FAP: (15.96±2.78)° (left), (17.20±3.44)° (right), t=-0.882. There were no significant differences between the left and right sides (P>0.05). Conclusion Using point A and P as referent indexes, the bony structures which represent the corresponding nerves and blood vessels can be precisely located for grinding Kawase triangle via intradural anterior transpetrosal approach. Key words: Intradural anterior transpetrosal approach; Arcuate eminence; Petrous apex; Location

Facial nerve morphogenesis: three‐dimensional and multiplanar study

The purpose of this study was to describe the facial nerve embryology, using three‐dimensional reconstructions from human embryos histological sections, and to compare our results with literature. Human embryos stage 13 to 21 from Carnegie collection and Paris‐Descartes University's Delmas‐Rouvière collection stained with hematoxylin &amp; eosin or Masson's trichrome were used. A local made computer software developed by IADI lab (INSERM U947, Nancy) allowed automatic slices selection, automatic rigid registration, and dust filtering. Once registration had been completed, DICOM files were used with ORS Visual software (v1.5, Montreal), which allowed multiple display and post‐processing possibilities (3D VR; orthogonal/curved multiplanar reformation). Due to large size files, image processing was performed on PC with Windows 7 (64 bit) and 20 GB RAM. Three‐dimensional and multiplanar study of the facial nerve morphogenesis was possible with appropriate thresholding. The size, shape and positional changes of the facial nerve, geniculate ganglion, greater petrosal nerve and chorda tympanic relative to the external and middle ear were studied. Human embryonic facial nerve morphogenesis works are very rare because of the smallness of this anatomical structure. Our study using historic human embryos histological sections has shown the facial nerve growth. The precise knowledge of this morphogenesis will help to better understand congenital malformations.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Fetal facial nerve course in the ear region revisited

The aim of this study was to re-examine the structures that determine course of the facial nerve (FN) in the fetal ear region. We used sagittal or horizontal sections of 28 human fetuses at 7-8, 12-16, and 25-37weeks. The FN and the chorda tympani nerve ran almost parallel until 7 weeks. The greater petrosal nerve (GPN) ran vertical to the distal FN course due to the trigeminal nerve ganglion being medial to the geniculate ganglion at 7weeks. Afterwards, due to the radical growth of the former ganglion, the GPN became an anterior continuation of the FN. The lesser petrosal nerve ran straight, parallel to the FN at 7weeks, but later, it started to wind along the otic capsule, possibly due to the upward invasion of the tympanic cavity epithelium. Notably, the chorda tympanic nerve origin from the FN, and the crossing between the vagus nerve branch and the FN, was located outside of the temporal bone even at 37weeks. The second knee of the FN was not evident, in contrast to the acute anterior turn below the chorda tympanic nerve origin. In all examined fetuses, the apex of the cochlea did not face the middle cranial fossa, but the tympanic cavity. Topographical relation among the FN and related nerves in the ear region seemed not to be established in the fetal age but after birth depending on growth of the cranial fossa.

Hypogeusia and High Signals in the Nuclei of the Solitary Tract on MRI due to Varicella-Zoster Virus Infection: A Case Report

A 63-year-old man noticed hypogeusia after presenting hiccups for several days. He was serologically diagnosed with varicella-zoster virus (VZV) infection, but had no skin lesions typical of herpes (zoster sine herpete). Hypogeusia was confirmed by electrogustometry and the filter-paper disk method, which showed damage in the areas innervated by the cord of tympanum, glossopharyngeal nerve, and greater petrosal nerve. High signals in the nuclei of the solitary tract of the medulla oblongata and the enhancement of the bilateral intracranial segments of the cranial nerve IX and X complex were observed by magnetic resonance imaging (MRI). The signal changes in the nuclei of the solitary tract on MRI were seen for more than 2 months, and hypogeusia lasted for more than 7 months. Hypogeusia caused by VZV infection has rarely been reported; however, similar cases could have gone undiagnosed or underdiagnosed in patients with idiopathic hypogeusia. (Received August 18, 2016; Accepted September 29, 2016; Published February 1, 2017).

Using Tympanometry to Evaluate Middle Ear Function in Children and Adolescents with Signs of Peripheral Facial Nerve Palsy

Facial nerve is the seventh paired cranial nerve. The main trunk of CN VII consists of motor fibers and the intermediate nerve which is a part of CN VII has parasympathetic and sensory fibers. One of the branches of CN VII is the chorda tympani which may play a significant role in responses related to normal Eustachian tube function. Other branches of CN VII, such as the greater petrosal nerve and tympanic branch, have motor fibers that open the Eustachian tube, which connects the tympanic cavity with the nasopharynx. It is located at the base of the cranium and consists of bone and cartilage. To evaluate the Eustachian tube and middle ear function, impedance audiometry (IA) is used. It is specifically used in hearing organ evaluation in children. The impedance audiometry consists of tympanometry, registration of reflex from the stapedius muscle and evaluation of Eustachian tube function. Tympanometry is an examination, evaluating response of the tympanic membrane and related structures of the middle ear on artificially induced pressure changes in the external auditory meatus. The main aim of the article is to evaluate middle ear function in children and adolescents with peripheral facial nerve palsy using results obtained in tympanometry and comparing the values for pressure, amplitude, and tympanometric curve gradient between the side with CV VII palsy (affected side) and the opposite side (healthy side).

The cochlea in skull base surgery: an anatomy study.

OBJECTIVE The object of this study was to examine the relationships of the cochlea as a guide for avoiding both cochlear damage with loss of hearing in middle fossa approaches and injury to adjacent structures in approaches directed through the cochlea. METHODS Twenty adult cadaveric middle fossae were examined using magnifications of ×3 to ×40. RESULTS The cochlea sits below the floor of the middle fossa in the area between and below the labyrinthine segment of the facial nerve and greater petrosal nerve (GPN) and adjacent to the lateral genu of the petrous carotid. Approximately one-third of the cochlea extends below the medial edge of the labyrinthine segment of the facial nerve, geniculate ganglion, and proximal part of the GPN. The medial part of the basal and middle turns are the parts at greatest risk in drilling the floor of the middle fossa to expose the nerves in middle fossa approaches to the internal acoustic meatus and in anterior petrosectomy approaches. Resection of the cochlea is used selectively in extending approaches through the mastoid toward the lateral edge of the clivus and front of the brainstem. CONCLUSIONS An understanding of the location and relationships of the cochlea will reduce the likelihood of cochlear damage with hearing loss in approaches directed through the middle fossa and reduce the incidence of injury to adjacent structures in approaches directed through the cochlea.

Cochlear implantation through the middle fossa: an anatomic study for a novel technique

Conclusion: The technique proposed is simple, reliable, and provides sufficient exposure of the basal portion of the cochlea while avoiding disabling complications. It enables visualization of the cochlear basal turn and the osseous spiral lamina, facilitating the insertion of the cochlear implant array through the scala tympani. Objectives: To describe a novel approach for exposing the cochlear basal turn for cochlear implantation through the middle cranial fossa. Methods: Fifty temporal bones were dissected and a cochleostomy was performed via a middle fossa approach on the most superficial part of the cochlear basal turn, using the superior petrosal sinus, the skeletonized petrous apex, the lateral surface of the meatal plane trailed on the petrous apex from its most proximal portion, and the great superficial petrosal nerve as landmarks. The distance between the landmarks and the distance between the cochleostomy and the round window were measured. Results: In all temporal bones, only the top portion of the cochlear basal turn was uncovered. The cochleostomy allowed both the scala tympani and the vestibule to be exposed. A computed tomography scan of the temporal bones was performed to document the electrode insertion from the cochlear basal turn until its apex. The mean ± SD minor and major distances between the cochleostomy and the meatal plane were estimated to be 2.48 ± 0.88 mm and 3.11 ± 0.86 mm, respectively. The mean distance from the cochleostomy to the round window was 8.38 ± 1.96 mm, and that to the superior petrosal sinus was 9.19 ± 1.59 mm. The mean minor and major distances between the cochleostomy and the long axis of the meatal plane from its most proximal portion were estimated to be 6.63 ± 1.38 mm and 8.29 ± 1.43 mm, respectively.

Clinical anatomy of greater petrosal nerve and its surgical importance

Background: Surgical approach towards greater petrosal nerve has to be done with caution as many surgeons are unfamiliar with the anatomy of the facial nerve. The anatomical landmarks selected must be reliable and above all easy to identify for identification of the greater petrosal nerve so as to avoid injury to the structures in the middle cranial fossa. Observation and Results: The present study is carried out on 100 temporal bones by examining the following measurements of the right and the left sides a) length of the hiatus for grater petrosal superficial nerve b) distance from superior petrosal sinus c) distance from lateral margin of middle cranial fossa d) arcuate eminence and e) distance from exit to the foramen ovale. Discussion: The anatomical landmarks selected must be reliable and above all easy to identify. Bony structures are more suitable than soft tissue or cartilaginous landmarks because of their rigid and reliable location. These anatomical landmarks will definitely help the surgeon while performing vidian nerve neurectomy and also the anatomical relationship of the facial nerve in temporal bone. The middle fossa approach involves a temporal craniotomy in cases of perineural spread of adenoid cystic carcinomas hence these anatomical landmarks will serve as useful guide for the surgeons and radiologists.

Subtemporal Epidural and Interdural Approach for the Greater Petrosal Nerve Schwannomas

Schwannomas arising from the greater petrosal nerve (GPN) are exceedingly rare: only 10 such cases have been reported in the English literature. We report on 4 cases of GPN schwannomas and discuss the surgical approach for their removal. 4 patients with GPN schwannomas underwent surgery at Keio University Hospital We present the pre- and postoperative clinical findings and describe the structures around the GPN schwannomas as observed during the surgery. Histological sections were performed around the GPN using Masson's trichrome stain to elucidate the membrane structures. Three patients presented with xerophthalmia, and one with facial palsy, hearing disturbance, and generalized convulsions. Contrast-enhanced magnetic resonance (MR) images revealed tumors in the temporal lobe. Bone-window computed tomography (CT) showed erosion of the anterior petrous apex. During the operation, the temporal lobe was retracted epidurally. The tumors were visible inside the interdural space and covered with the epineurium. In three cases, the tumors were completely removed, and in one case the tumor was subtotally removed with intraoperative facial monitoring. In the histological sections, we confirmed that the GPN ran within the interdural space.

Dissection and Exposure of the Whole Course of Deep Nerves in Human Head Specimens after Decalcification

The whole course of the chorda tympani nerve, nerve of pterygoid canal, and facial nerves and their relationships with surrounding structures are complex. After reviewing the literature, it was found that details of the whole course of these deep nerves are rarely reported and specimens displaying these nerves are rarely seen in the dissecting room, anatomical museum, or atlases. Dissections were performed on 16 decalcified human head specimens, exposing the chorda tympani and the nerve connection between the geniculate and pterygopalatine ganglia. Measurements of nerve lengths, branching distances, and ganglia size were taken. The chorda tympani is a very fine nerve (0.44 mm in diameter within the tympanic cavity) and approximately 54 mm in length. The mean length of the facial nerve from opening of internal acoustic meatus to stylomastoid foramen was 52.5 mm. The mean length of the greater petrosal nerve was 26.1 mm and nerve of the pterygoid canal was 15.1 mm.

A rare case of greater petrosal nerve schwannoma

Background:Facial nerve schwannomas include only 0.8% of all intrapetrous mass lesions, and schwannomas originating exclusively from the greater petrosal nerve (GPN) are extremely rare. To date, only 13 reports have been described. In this case, the tumor was thought to originate from the GPN on the basis of clinical, radiological, and operative findings.Case Description:A 23-year-old girl presented an acute left facial palsy, a disturbance in tear secretion of the ipsilateral eye, and a left-sided conductive hypoacusia. Computed tomography (CT) scan and magnetic resonance imaging (MRI) showed an extradural mass in the left middle fossa. A subtemporal approach was performed and the lesion, originating from the proximal portion of the GPN, was excised. The post-operative course was satisfactory, except for a xerophtalmia, which was treated with artificial teardrops.Conclusion:GPN schwannomas can originate anywhere alongside the course of the nerve, from its proximal segment near the facial hiatus to its distal segment near the foramen lacerum. For these reasons, it requires differential diagnosis with trigeminal nerve schwannomas or with injuries arising from the geniculate ganglion, because it can be easily confused with those lesions. However, in less severe cases, an early diagnosis can be able to preserve the function of the facial nerve by reducing iatrogenic injuries caused by surgical maneuvers.

Arachnoid granulations of the middle cranial fossa

We would like to applaud Chen et al. [2] on a superb study evaluating other locations of arachnoid granulations within the middle cranial fossa. These data help explain and further elucidate possible cerebrospinal Xuid absorption that occurs outside of the large arachnoid granulations found within the superior sagittal sinus and lacunae lateralis (Weed [4] Wrst described CSF reabsorption via the arachnoid granulations along the superior sagittal sinus in 1923). This is exempliWed in patients who have partial occlusion of the superior sagittal sinus but do not develop hydrocephalus. It is noteworthy that standard sources and textbooks usually do not mention such non-superior sagittal sinus/lateral lacunae locations. Other less known sites have been found along cranial nerves as they exit the cranium (e.g. jugular foramen), in the internal auditory meatus near the greater petrosal nerve’s emergence from the geniculate ganglion, and from the sheath of the trigeminal nerve as its parts traverse the cavernous sinus [1]. Additionally, these structures or at least arachnoid villi are identiWed along the spinal axis particularly at the nerve root sleeves [3]. We look forward to additional studies by these authors.

Greater petrosal nerve schwannomas—analysis of four cases and review of the literature

Schwannomas arising from the greater petrosal nerve (GPN) are exceedingly rare: only 10 such cases have been reported in the English literature. We report on four cases of GPN schwannomas and discuss the surgical approach for their removal. Four patients with GPN schwannomas underwent surgery at Keio University Hospital. We present the pre- and postoperative clinical findings and describe the structures around the GPN schwannomas as observed during the surgery. Histological sections were performed around the GPN using Masson's trichrome stain to elucidate the membrane structures. Three patients presented with xerophthalmia, and one with facial palsy, hearing disturbance, and generalized convulsions. Contrast-enhanced magnetic resonance images revealed tumors in the temporal lobe. Bone-window computed tomography showed erosion of the anterior petrous apex. During the operation, the temporal lobe was retracted epidurally. The tumors were visible inside the interdural space and covered with the epineurium. In three cases, the tumors were completely removed, and in one case, the tumor was subtotally removed with intraoperative facial monitoring. In the histological sections, we confirmed that the GPN ran within the interdural space. Approaching epi- and interdurally is suitable for the removal of GPN schwannomas because the GPN is located within the interdural space. The advantage of this approach is that the landmark points can be identified. Moreover, the possibility of injuring the temporal lobe is low because the temporal lobe is not exposed in this approach.

MICROSURGICAL AND ENDOSCOPIC ANATOMY OF THE VIDIAN CANAL

The vidian canal, the conduit through the sphenoid bone for the vidian nerve and artery, has become an important landmark in surgical approaches to the cranial base. The objective of this study was to examine the anatomic features of the vidian canal, nerve, and artery, as well as the clinical implications of our findings. Ten adult cadaveric specimens and 10 dried skulls provided 40 vidian canals for examination with x 3 to x 20 magnification and the endoscope. The paired vidian canals are located in the skull base along the line of fusion of the pterygoid process and body of the sphenoid bone. The canal opens anteriorly into the medial part of the pterygopalatine fossa and posteriorly at the upper part of the anterolateral edge of the foramen lacerum. The vidian nerve, when followed posteriorly, reaches the lateral surface of the anterior genu of the petrous carotid and the anteromedial part of the cavernous sinus where the nerve is continuous with the greater petrosal nerve. The bone surrounding the upper part of 12 of 20 vidian canals protruded into the floor of the sphenoid sinus and one canal had a bony dehiscence that exposed its contents under the sinus mucosa. Nine petrous carotid arteries (45%) gave rise to a vidian artery, all of which anastomosed with the vidian branch of the maxillary artery in the vidian canal or pterygopalatine fossa. The vidian canal can be exposed by opening the floor of the sphenoid sinus, the posterior wall of the maxillary, the posterior part of the lateral wall of the nasal cavity, and the medial part of the floor of the middle fossa. The vidian canal and nerve are important landmarks in accessing the anterior genu of the petrous carotid, anteromedial part of the cavernous sinus, and petrous apex.

An efficient approach to teaching the anatomy of the middle ear cavity to first year medical students using digital images of prosected cadavers

Dissection of the middle ear cavity is challenging and time consuming, often resulting in a frustrating learning experience for students. Consequently, courses in gross anatomy may omit dissection of the middle ear, or revert to dissections on decalcified temporal bones, or rely on time consuming, faculty‐prepared prosections. At our school, we have developed an efficient laboratory experience to teach middle ear anatomy using faculty‐prepared prosections and digital imaging. Prosections are done in 15–20 minutes using a quick dissection technique (Anat. Rec. 181:685, 1975) that involves fracturing through the petrous part of the temporal bone. Thus, multiple specimens can be prepared in a short time. This exposure reveals the malleus and incus, the geniculate ganglion and course of the facial nerve, the chorda tympani and greater petrosal nerves, the tensor tympani, the tympanic membrane, the opening of the auditory tube, and the mastoid area. High resolution photos, taken using a macro lens on a digital camera, are enhanced, colorized, and labeled using Photoshop. Color prints (8” × 11”) are placed adjacent to the prosections so students can study the specimens without faculty assistance. This approach is curriculum friendly since it does not require additional lab time as students can exam the middle ear prosections during other scheduled labs. Our approach has proved successful for teaching clinically relevant anatomy of the middle ear in an effective, efficiently manner with neither students nor faculty spending large amounts of time in the laboratory setting.

Cochlear implantation via the middle fossa: surgical and electrode array considerations

Cochlear implantation via the middle cranial fossa may access the entire length of the cochlea without opening the middle ear. Concerns include safety and electrode array design. The objectives of this study were to determine the depth to the superior portion of the basal turn (SPBT) and distances from the facial and greater petrosal nerves, and to describe some ideas about electrode arrays. The study involved operative dissection of 41 bequeathed otitis-free adult crania (82 temporal bones). Mastoid size was assessed by x-ray. Commercially available MED-EL split arrays were inserted. The depth from the floor of the middle cranial fossa to SPBT of the cochlea ranged from 0.5 mm to 4.2 mm. Small mastoid size correlated with shallow depth. Distances from the centre of the SPBT to the labyrinthine portion of the facial nerve, to the geniculate ganglion, and to the greater petrosal nerve ranged from 1.0 mm to 3.0 mm, 2.0 mm to 3.2 mm, and 1.8 mm to 2.8 mm, respectively. More than 75% of electrodes inserted toward the round window extended into the vestibule. Insertions toward the cochlear apex had a median insertion depth of 12 mm (range 6 mm to 18 mm). The middle cranial fossa approach appears safe and allows electrode access to nearly the full length of the cochlea. Electrode arrays specific for this route of implantation are needed, together with a rigorous study comparing outcomes of this route of implantation with traditional implantation through the facial recess. Copyright © 2007 John Wiley & Sons, Ltd.

The earliest known member of the rorqual—gray whale clade (Mammalia, Cetacea)

ABSTRACT Eobalaenoptera harrisoni, gen. et sp. nov., is described from a partial skeleton collected from the middle Miocene Calvert Formation of Virginia. Characteristics of this taxon, particularly of the petrosal, indicate that the new whale is a member of the clade that includes the Balaenopteridae (rorquals) and Eschrichtidae (gray whales) to the exclusion of “cetotheres” and the Balaenidae (right whales). Some of the probable synapomorphies of this clade include an elongate pars cochlearis, a tubular internal auditory meatus, the greater petrosal nerve foramen on the tympanic side of the petrosal, the stylomastoid fossa extending onto the posterior process of the petrosal, no medial groove on the pars cochlearis, four digits on each forelimb, depressed supraorbital processes, and ascending processes of maxillae extending onto the vertex. The approximate 14-million-year age of the specimen makes it the oldest known member of the clade by some 3 to 5 million years, and extends the fossil record of this clade closer to the divergence time estimated by some recent molecular studies.

Localization of preganglionic neurons that innervate choroidal neurons of pterygopalatine ganglion.

The pterygopalatine ganglion (PPG) receives preganglionic input from the superior salivatory nucleus (SSN) of the facial motor complex and is the main source of parasympathetic input to the choroid in mammals. The present study was undertaken to determine in rats the location and neurotransmitters of SSN neurons innervating those PPG neurons that target the choroid and to determine the location and neurotransmitters of the PPG choroidal neurons themselves. Retrograde labeling from rat choroid using a fluorescent tracer, in combination with immunofluorescence labeling for nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP), and choline acetyltransferase (ChAT), was used to characterize the location and neurotransmitters of choroidal PPG neurons. To identify SSN neurons that innervate the choroidal PPG neurons, the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV-Ba) was injected into rat choroid, and immunolabeling for NOS or ChAT was used to characterize their neurochemistry. Fluorescent retrograde labeling showed that PPG neurons projecting to the choroid contained NOS, VIP, and ChAT and were widely distributed in PPG and its preganglionic root, the greater petrosal nerve. SSN neurons were ChAT(+), and a subset of them was found to contain NOS. PRV-Ba transneuronal retrograde labeling revealed that choroidal preganglionic neurons were localized to the rostral medioventral part of the ipsilateral SSN. The choroidal SSN neurons were ChAT(+) and appeared largely to correspond to the NOS(+) neurons of the SSN. These results show that preganglionic neurons in rats that are presumed to regulate choroidal blood flow through the PPG reside within the rostral medioventral SSN, and that NOS is a marker for these SSN neurons.