Microanatomic analysis of the trigeminal nerve and potential nerve graft donor sites

The Ansa Hypoglossi: Quantifying Axonal Density of a Donor Nerve for Facial Reinnervation

Background: There are a number of nerve grafting options for facial reanimation and the ansa hypoglossi (AH) may be considered in select situations. Objective: To compare axonal density, area, and diameter of AH with other nerves more usually used for facial reanimation. Methods: AH specimens from patients undergoing neck dissections were submitted in formalin. Proximal to distal cross sections, nerve diameters, and the number of axons per nerve, proximally and distally, were measured and counted. Results: Eighteen nerve specimens were analyzed. The average manual axon count for the distal and proximal nerve sections was 1378 ± 333 and 1506 ± 306, respectively. The average QuPath counts for the proximal and distal nerve sections were 1381 ± 325 and 1470 ± 334, respectively. The mean nerve area of the proximal and distal nerve sections was 0.206 ± 0.01 and 0.22 ± 0.064 mm2, respectively. The mean nerve diameter for the proximal and distal nerve sections were 0.498 ± 0.121 and 0.526 ± 0.75 mm, respectively. Conclusion: The histological characteristics of the AH support clinical examination of outcomes as a promising option in facial reanimation.

Neuropathy Score Reporting and Data System (NS-RADS): MRI Reporting Guideline of Peripheral Neuropathy Explained and Reviewed

A standardized guideline and scoring system should be used for the MR imaging diagnosis of peripheral neuropathy. The MR imaging-based Neuropathy Score Reporting and Data System (NS-RADS) is a newly devised classification system (in press in AJR) that can be used to communicate both type and severity of peripheral neuropathy in the light of clinical history and examination findings. The spectrum of neuropathic conditions and peripheral nerve disorders covered in this system includes nerve injury, entrapment, neoplasm, diffuse neuropathy, and post-interventional states. This classification system also describes the temporal MR imaging appearances of regional muscle denervation changes. This review article is based on the multicenter validation study pre-published in American journal of Roentgenology and discusses technical considerations of optimal MR imaging for peripheral nerve evaluation and discusses the NS-RADS classification and its severity scales with illustration of conditions that fall under each classification. The readers can gain knowledge of the NS-RADS classification system and learn to apply it in their practices for improved inter-disciplinary communications and timely patient management.

A comprehensive review of the great auricular nerve graft

The great auricular nerve (GAN) is a superficial branch of the cervical plexus that innervates parts of the mandible, auricle, and earlobe. Over the past 30 years, the GAN has become the nerve graft donor of choice for many surgeons for reconstructing injured facial nerves. In this review, we discuss the anatomy and function of the GAN, while focusing on surgical landmarks and the characteristics that make it a suitable nerve graft donor. In addition, we present and summarize published case reports on use of the GAN for grafting. We hope that this review will provide surgeons with an up-to-date and concise reference.

Sensory Restoration of the Facial Region

Normal sensitivity of the face is very important for preserving its integrity and function as an efferent source of information for the brain. The trigeminal nerve, which is the largest cranial nerve, conducts most of facial sensory function through its 3 branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The trigeminal nerve may be damaged by a variety of etiologies including inflammatory disorders, brain tumor resection, trauma, iatrogenic injury, or congenital anomalies. Temporary or permanent damage can lead to numbness, lip-biting injury, corneal anesthesia, and, in the worst scenario, even blindness. Different age groups, mechanisms of the injury, and the time between injury and repair can affect the final result of the nerve repair. Unlike the well-understood facial nerve palsy, so far there is no universal approach to restore the facial sensory function. This article serves to thoroughly review the basic anatomy of trigeminal nerve, diagnosis of sensory nerve dysfunction, and attempts to establish a protocol for treatment and rehabilitation of affected patients.

Surgical anatomy of the ovine sural nerve for facial nerve regeneration and reconstruction research

The lack of a clinically relevant animal models for research in facial nerve reconstruction is challenging. In this study, we investigated the surgical anatomy of the ovine sural nerve as a potential candidate for facial nerve reconstruction, and performed its histological quantitative analysis in comparison to the buccal branch (BB) of the facial nerve using cadaver and anesthetized sheep. The ovine sural nerve descended to the lower leg along the short saphenous vein. The length of the sural nerve was 14.3 ± 0.5 cm. The distance from the posterior edge of the lateral malleolus to the sural nerve was 7.8 ± 1.8 mm. The mean number of myelinated fibers in the sural nerve was significantly lower than that of the BB (2,311 ± 381vs. 5,022 ± 433, respectively. p = 0.003). The number of fascicles in the sural nerve was also significantly lower than in the BB (10.5 ± 1.7 vs. 21.3 ± 2.7, respectively. p = 0.007). The sural nerve was grafted to the BB with end-to-end neurorrhaphy under surgical microscopy in cadaver sheep. The surgical anatomy and the number of fascicles of the ovine sural nerve were similar of those reported in humans. The results suggest that the sural nerve can be successfully used for facial nerve reconstruction research in a clinically relevant ovine model.

Anterior Greater Auricular Point: Novel Anatomic Landmark to Facilitate Harvesting of the Greater Auricular Nerve

BACKGROUND

The greater auricular nerve (GAN) may be used as a nerve graft during neurosurgical procedures to repair damaged nerves. There is extensive literature on localization of the GAN at the posterior triangle of the neck, but objective information on localization of the GAN at the anterior triangle of the neck close to cranial neurosurgical fields is lacking. The aim of this study was to introduce simple and reliable landmarks to localize the GAN at the anterior triangle of the neck to facilitate its harvest during neurosurgical procedures.

METHODS

The GAN was exposed bilaterally in 11 cadaveric specimens at the point of crossing the anterior border of the sternocleidomastoid muscle (anterior greater auricular point [AGA]). Distances from the AGA point to the angle of the mandible and the tip of the mastoid process were measured. Additionally, the location of the crossing point between the GAN and an imaginary line passing through the mastoid tip and the angle of the mandible (M-A line) was found relative to these bony landmarks.

RESULTS

Mean (±SD) distances from the AGA point to the mastoid tip and the angle of the mandible were 29.1 ± 3.4 mm and 27.5 ± 4.5 mm, respectively. The GAN was always found to cross the M-A line in its middle third (mean 48.2% ± 6.9% from the mastoid tip).

CONCLUSIONS

The AGA point and the M-A line are reliable landmarks for locating the GAN at the anterior triangle of the neck and for helping neurosurgeons expose and harvest the GAN efficiently.

Association between pain severity and clinicohistopathologic findings in the mandibular canal and inferior alveolar nerve of patients with advanced mandibular osteoradionecrosis

OBJECTIVE

Pain is one of the most problematic symptoms in patients with osteoradionecrosis of the jaws. This study investigated the associations between pain severity and morphologic alterations of the mandibular canal and inferior alveolar nerve, in respective computerized tomography images and resected specimens of mandibular osteoradionecrosis.

STUDY DESIGN

We assessed 14 lesions in 13 patients who underwent segmental mandibulectomy for surgical debridement and simultaneous reconstruction with free fibula flap (1 patient exhibited bilateral lesions). The extent of the mandibular canal bone defect on preoperative coronal computerized tomography images and the number of inferior alveolar nerve fascicles in resected specimens were evaluated. Comparisons were made between the slight pain and extreme pain groups. In most of the patients in the extreme pain group, either mandibular canal bone defects were absent or entire circumferential defects were present; inferior alveolar nerve fascicles were either distinguishable or completely absent in the resected specimens.

RESULTS

Although there was no statistically significant association between extreme pain and computerized tomography or histopathologic findings, the histopathologically indistinguishable inferior alveolar nerve fascicles was significantly associated with slight pain.

CONCLUSIONS

The degree of degeneration of mandibular canal and inferior alveolar nerve may be associated with pain severity in patients with mandibular osteoradionecrosis.

Anatomic and histological study of great auricular nerve and its clinical implication

BACKGROUND

The great auricular nerve (GAN) is often sacrificed during parotidectomy, rhytidectomy, and platysma flap operation. Transection of the nerve results in a wooden numbness of preauricular region, pain, and neuroma. The aim of this study was to describe the branching patterns and distribution area of the GAN.

METHODS

Twenty-five embalmed, adult hemifacial Korean cadavers (16 males, nine females; mean age 62.5 years) were used in this study. The branching of the GAN was determined through careful dissection. The histological structure of the GAN was also examined by harvesting and sectioning specimens, and then viewing them with the aid of a light microscope.

RESULTS

The branching pattern of the anterior, posterior, deep, and superficial branches of the GAN could be classified into five types: type I (20%), where the deep branches arose from the anterior branch; type II (24%), where all branches originated at the same point; type III (28%), where the deep branch arose from the posterior branch; type IV (8%), where the superficial branches arose from the posterior branch; and type V (20%), where the anterior and posterior branches ran independently. A connection between the GAN and the facial nerve trunk was observed in all specimens, and a connection with the auriculotemporal nerve was observed in a few specimens. The total fascicular area of both regions decreased from proximal (1.42 mm2) to distal (0.60 mm2). There were 2.5 and 5 fascicles in the proximal and distal regions, respectively.

CONCLUSION

The results reported herein will help toward preservation of the GAN during surgery in the region of the parotid gland. Furthermore, the histologic findings suggest that the GAN would be a good donor site for nerve grafting.

Interventions for iatrogenic inferior alveolar and lingual nerve injury

BACKGROUND

Iatrogenic injury of the inferior alveolar or lingual nerve or both is a known complication of oral and maxillofacial surgery procedures. Injury to these two branches of the mandibular division of the trigeminal nerve may result in altered sensation associated with the ipsilateral lower lip or tongue or both and may include anaesthesia, paraesthesia, dysaesthesia, hyperalgesia, allodynia, hypoaesthesia and hyperaesthesia. Injury to the lingual nerve may also affect taste perception on the affected side of the tongue. The vast majority (approximately 90%) of these injuries are temporary in nature and resolve within eight weeks. However, if the injury persists beyond six months it is deemed to be permanent. Surgical, medical and psychological techniques have been used as a treatment for such injuries, though at present there is no consensus on the preferred intervention, or the timing of the intervention.

OBJECTIVES

To evaluate the effects of different interventions and timings of interventions to treat iatrogenic injury of the inferior alveolar or lingual nerves.

SEARCH METHODS

We searched the following electronic databases: the Cochrane Oral Health Group's Trial Register (to 9 October 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 9), MEDLINE via OVID (1946 to 9 October 2013) and EMBASE via OVID (1980 to 9 October 2013). No language restrictions were placed on the language or date of publication when searching the electronic databases.

SELECTION CRITERIA

Randomised controlled trials (RCTs) involving interventions to treat patients with neurosensory defect of the inferior alveolar or lingual nerve or both as a sequela of iatrogenic injury.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by The Cochrane Collaboration. We performed data extraction and assessment of the risk of bias independently and in duplicate. We contacted authors to clarify the inclusion criteria of the studies.

MAIN RESULTS

Two studies assessed as at high risk of bias, reporting data from 26 analysed participants were included in this review. The age range of participants was from 17 to 55 years. Both trials investigated the effectiveness of low-level laser treatment compared to placebo laser therapy on inferior alveolar sensory deficit as a result of iatrogenic injury.Patient-reported altered sensation was partially reported in one study and fully reported in another. Following treatment with laser therapy, there was some evidence of an improvement in the subjective assessment of neurosensory deficit in the lip and chin areas compared to placebo, though the estimates were imprecise: a difference in mean change in neurosensory deficit of the chin of 8.40 cm (95% confidence interval (CI) 3.67 to 13.13) and a difference in mean change in neurosensory deficit of the lip of 21.79 cm (95% CI 5.29 to 38.29). The overall quality of the evidence for this outcome was very low; the outcome data were fully reported in one small study of 13 patients, with differential drop-out in the control group, and patients suffered only partial loss of sensation. No studies reported on the effects of the intervention on the remaining primary outcomes of pain, difficulty eating or speaking or taste. No studies reported on quality of life or adverse events.The overall quality of the evidence was very low as a result of limitations in the conduct and reporting of the studies, indirectness of the evidence and the imprecision of the results.

AUTHORS' CONCLUSIONS

There is clearly a need for randomised controlled clinical trials to investigate the effectiveness of surgical, medical and psychological interventions for iatrogenic inferior alveolar and lingual nerve injuries. Primary outcomes of this research should include: patient-focused morbidity measures including altered sensation and pain, pain, quantitative sensory testing and the effects of delayed treatment.

Autogenous grafts/allografts/conduits for bridging peripheral trigeminal nerve gaps

Nerve repairs and grafting techniques have been around for many years. Autogenous nerve grafts have worked reasonably well in the right circumstances but are associated with difficulties in achieving a proper donor-host match and with postsurgical sequelae at the donor site. Vein grafts seem to work almost as well as autogenous nerve grafts in digital nerve repairs that require a graft less than 3 cm in length. Currently, the most promising nerve graft materials are the polyglycolic acid tubes and processed decellularized allografts, which have shown good results without the morbidity of autogenous nerve grafts. However, more research studies using these materials for TN repairs are essential to validate the superiority of these procedures.

Morphometric analysis of the inferior alveolar nerve fails to demonstrate sexual dimorphism

PURPOSE

With regard to the incidence of inferior alveolar nerve (IAN) damage after an IAN block or following oral and maxillofacial surgical procedures, there are reports of sexual dimorphism, no sexual dimorphism, and little sexual dimorphism. However, details of the morphology and sexual dimorphism in the characteristics of the IAN have not been available in textbooks. We morphometrically analyzed the human IAN and clarified these issues.

MATERIALS AND METHODS

The materials were obtained from 22 cadavers (11 female and 11 male), aged 59 to 84 years (average age: 74.1 yr), and dentulous. The causes of death did not influence the nervous system, so the IANs were considered to be normal. Human IANs were resected at the mandibular foramen. We counted the myelinated axons and measured the transverse area, perimeter, and circularity ratio of the myelinated axons.

RESULTS

We estimated the average total number of myelinated axons in the female IAN to be 25,230, with an average transverse area of 34.1 microm(2), an average perimeter of 21.8 microm, and an average circularity ratio of 0.86, with the same measurements in the male IAN being 20,278, 31.7 microm(2), 20.7 microm, and 0.87, respectively. Our data showed no significant difference between the female and male specimens in any measured item (P < .05).

CONCLUSIONS

We assumed that the sex difference in the incidence of IAN damage was not affected by the morphometric findings. Our findings might partly explain why there is no significant sex difference in the incidence of IAN damage.

Facial nerve repair with expanded polytetrafluoroethylene and collagen conduits: an experimental study in the rabbit

PURPOSE

This study evaluated autogenous nerve grafts and expanded polytetrafluoroethylene (e-PTFE) and collagen tubes as conduits for the repair of continuity defects in the facial nerve of rabbits.

MATERIALS AND METHODS

The buccal division of 24 facial nerves was isolated, transected, and separated 10 mm. The gap between the 2 nerve ends was then repaired with an autologous nerve graft or an e-PTFE or collagen conduit. Fifteen days and 1, 2, and 4 months after the procedure, the animals were subjected to electrophysiologic tests, killed, and the nerves were removed for histologic examination.

RESULTS

At 15 days postsurgery, no regeneration was observed through the e-PTFE and collagen tubes or across the autologous nerve grafts at the midpoint of the specimens. However, regeneration across the chambers and autologous nerve grafts was seen in the following 4 months, although the number of axons regenerated was small.

CONCLUSIONS

The results of the study indicate that e-PTFE and collagen tubing may be effective in the repair of continuity defects in peripheral nerves. However, further research will be necessary for generalization of this procedure.

Inferior alveolar nerve function after sagittal split osteotomy of the mandible: correlation with degree of intraoperative nerve encounter and other variables in 496 operations

Dysfunction of the inferior alveolar nerve indicated by various degrees of numbness of the lower lip and chin is one of the few drawbacks of sagittal split osteotomy (SSO) of the mandible. Although it has been recorded throughout the history of this technique its true aetiology is poorly understood. In this study of 496 SSOs, we have evaluated possible correlations between neurosensory dysfunction and several variables that have been implicated, such as the age of the patient, mandibular movement, type of split technique and osteosynthesis, degree of intraoperative nerve encounter, and surgical skill. Nerve dysfunction developed after 200/496 SSOs (40%). The patient's age had a significant influence on the recovery of the neurosensory function. Intraoperative nerve encounter such as nerve manipulation correlated with dysfunction to a much lesser degree than expected. Surgical skill seemed to influence the recovery of neurosensory function after SSO, which is often referred to as a technique-sensitive procedure. We suggest that the dissection of the soft tissue on the medial aspect of the mandibular ramus might be partly responsible for nerve dysfunction of the lower lip and chin after SSO of the mandible.

Histological analysis of the greater auricular nerve and its use as a graft

Many factors are involved in successful nerve grafting. Morphometric similarity between donor and recipient nerve is one of these factors. A histological study was undertaken to determine the suitability of the greater auricular nerve as a graft in head and neck surgery. Nerves were obtained from fresh human cadavers and evaluated for length, total cross-sectional area, total fascicular cross-sectional area and fascicular number, at three separate points along the nerve. Comparisons were made with similar studies of the sural and facial nerve. The study confirms the clinical view that the greater auricular nerve is ideal when short sections of graft are required in head and neck surgery.

Microanatomic analysis of the medial antebrachial nerve as a potential donor nerve in maxillofacial grafting

PURPOSE

To histologically compare the anterior branch of the medial antebrachial cutaneous nerve (MACN) with the sural nerve using biometric techniques.

PATIENTS AND METHODS

Twenty-centimeter segments of the right and left (MACN) and sural nerves from three cadavers were analyzed. The number of fascicles within the nerves were counted and the neural to connective tissue ratio was estimated.

RESULTS

Sural nerves consistently showed greater amounts of connective tissue between the fascicles than the MACN. Fascicle diameter varied less throughout the length of the MACN. Fascicle diameter varied less throughout the length of the MACN and it showed fewer and larger fascicles, more closely approximating the anatomy of the inferior alveolar nerve.

CONCLUSION

These preliminary data suggest that the MACN, on anatomic grounds, is theoretically more suited for grafting to the alveolar and lingual nerves than the sural nerve.

Axon populations in cat lingual and chorda tympani nerves

The lingual and chorda tympani nerves from five cats were examined so that normal axonal populations could be determined. After perfusion fixation, the chorda tympani and lingual nerves were removed and processed, and sections were taken from individual and combined nerves for both light and electron microscopy. The chorda tympani remained as a distinct group of smaller axons for at least 4 mm distal to its junction with the lingual nerve. The mean number +/- S.D. of myelinated axons in the chorda tympani central to the junction was 1322 (+/- 268) and in the lingual nerve central to the junction, 3227 (+/- 510). The counts were not significantly different distal to the junction, and there were no side-to-side differences. Mean myelinated axon circumferences were significantly smaller in the chorda tympani (12.86 +/- 0.87) than in the lingual nerve (22.79 +/- 1.99; p less than 0.01). The mean size of axons in the chorda tympani was slightly but consistently larger on the left (13.1 +/- 0.73) than on the right side (12.61 +/- 1.01; p less than 0.05). Distal to the junction, the average proportion of non-myelinated axons was 44% in both chorda tympani and lingual nerves.