Anatomical analysis of the distribution patterns of occipital cutaneous nerves and the clinical implications for pain management

Sihler's staining of the anterior belly of digastric muscle for botulinum toxin injection

PURPOSE

The anterior belly of the digastric muscle (ABDM) is the target of botulinum toxin injection; however, anatomical considerations related to the injection point are absent. This study used Sihler's staining to analyze the intramuscular nerve distribution of ABDM to identify the most effective botulinum toxin injection points.

METHODS

We used 12 specimens from 6 embalmed cadavers in this study. The specimens were manually dissected to preserve the mylohyoid nerve and subjected to Sihler's staining. From the gnathion to and hyoid bone, the ABDM was divided into three equal parts, distinguishing the anterior, middle, and posterior thirds.

RESULTS

Only a branch of the mylohyoid nerve entered the ABDM, and its entry point was located in the middle-third region in all cases. The nerve endings were concentrated in the middle third (100%), followed by the anterior third (58.3%) and were not observed in the posterior third.

CONCLUSION

The landmarks used in this study (gnathion and hyoid bone) are easily palpable on the skin surface, allowing clinicians to target the most effective injection site (middle third of ABDM). These results provide scientific and anatomic evidence for injection points, and will aid in the management of ABDM injection procedures in clinical practice.

Challenges of Imaging the Greater Occipital Nerve Using Magnetic Resonance Imaging

ABSTRACT

Migraine headaches are a significant global health concern, frequently managed with varying levels of success. Compression of the greater occipital nerve (GON) is hypothesized to contribute to pathology in some migraine patients, making extracranial nerve decompression surgery a potential intervention for refractory cases. However, accurate methods to image the GON along its tortuous course still need to be explored. Our group has developed magnetic resonance imaging sequences to track the GON. Yet, many challenges were met, which included navigating the GON's complex anatomy, understanding anatomical variants, and designing advanced magnetic resonance imaging sequences and coils to image the posterior scalp. Addressing these hurdles is vital to capture and understand GON pathology and guide potential interventions.

An anatomical analysis of the occipital nerve complex: an essential tool for the application of occipital nerve blocks

BACKGROUND

Occipital nerve blocks are essential in diagnosing and treating headache disorders such as migraine, cervicogenic headache, occipital neuralgia, and cluster headache. In this study, we aimed to investigate the potential compression points of the greater occipital nerve (GON), third occipital nerve (TON), and lesser occipital nerve (LON) which are targeted to block in occipital nerve blocks and to develop a method to detect these points easily.

METHODS

To identify potential compression points of the GON, TON, and LON, we dissected 43, 41, and 26 cadavers, respectively. A rigid, transparent tool divided into 1 × 1 cm sections was placed on the external occipital protuberance to measure the determined points. The cadaveric head was viewed from above, vertically, and the coordinates corresponding to each point were noted separately.

RESULTS

Six, four, and one potential entrapment points were detected for the GON, TON, and LON, respectively. The distances of the point where the GON arose from the lower border of the obliquus capitis inferior muscle and the emerging point of the TON from the C2-C3 vertebrae to the posterior midline were statistically significant in terms of the sides (p = 0.040). Similarly, there was a statistical significance between genders for the distance of the point where the LON arose from the posterior edge of the sternocleidomastoid muscle to the posterior midline (p = 0.002).

CONCLUSIONS

We believe that with the method developed, the GON, TON, and LON compression points can be easily localized and blocked in diagnosing and treating patients experiencing headaches such as migraines, cervicogenic headaches, occipital neuralgia, and cluster headache.

3D anatomy of the supraorbital and greater occipital nerve trajectories

PURPOSE

This research aims to enhance understanding of the anatomy of the supraorbital nerve (SON) and greater occipital nerve (GON), focusing on their exit points, distal trajectories, and variability, utilizing a novel 3D representation.

METHODS

Ten cadaveric specimens underwent meticulous dissection, and 3D landmarks were registered. Models were generated from CT scans, and a custom 3D method was employed to visualize nerve trajectories. Measurements, including lengths and distances, were obtained for the SON and GON.

RESULTS

The SON exhibited varied exit points, with the lateral branches being the longest. The GON showed distinct branching patterns, which are described relative to various anatomical reference points and planes. No systematic left-right differences were observed for either nerve. 3D analysis revealed significant interindividual variability in nerve trajectories. The closest approximation between the SON and GON occurred between lateral branches.

CONCLUSION

The study introduces a novel 3D methodology for analyzing the SON and GON, highlighting considerable anatomical variation. Understanding this variability is crucial for clinical applications and tools targeting the skull innervation. The findings serve as a valuable reference for future research, emphasizing the necessity for personalized approaches in innervation-related interventions.

Morphological features of the greater occipital nerve and its possible importance for interventional procedures

Being one of the most prevalent neurological symptoms, headaches are burdensome and costly. Blocks and decompression surgeries of the greater occipital nerve (GON) have been frequently used for migraine, cervicogenic headache, and occipital neuralgia which are classified under headache by International Headache Society. Knowledge of complex anatomy of GON is crucial for its decompression surgery and block. This study was performed to elucidate anatomical features of this nerve in detail. Forty-one cadavers were dissected bilaterally. According to its morphological features, GON was classified into four main types that included 18 subtypes. Moreover, potential compression points of the nerve were defined. The number of branches of the GON up to semispinalis capitis muscle and the number of its branches that were sent to this muscle were recorded. The most common variant was that the GON pierced the aponeurosis of the trapezius muscle, curved around the lower edge of the obliquus capitis inferior muscle, and was loosely attached to the obliquus capitis inferior muscle (Type 2; 61 sides, 74.4%). In the subtypes, the most common form was Type 2-A (44 sides, 53.6%), in which the GON pierced the aponeurosis of each of the trapezius muscle and fibers of semispinalis muscle at one point and there was a single crossing of the GON and occipital artery. Six potential compression points of the GON were detected. The first point was where the nerve crossed the lower border of the obliquus capitis inferior muscle. The second and third points were at its piercing of the semispinalis capitis muscle and the muscle fibers/aponeurosis of the trapezius, respectively. Fourth, fifth, and sixth compression points of GON were located where the GON and occipital artery crossed each other for the first, second, and third times, respectively. On 69 sides, 1-4 branches of the GON up to the semispinalis capitis muscle were observed (median = 1), while 1-4 branches of GON were sent to the semispinalis capitis muscle on 67 sides (median = 1). The novel anatomical findings described in this study may play a significant role in increasing the success rate of invasive interventions related with the GON.

Literature Review: Pericranial Nerve Blocks for Chronic Migraines

Purpose of Review

Headaches, especially migraines, are one of the most pervasive neurological disorders affecting up to 15.9% of the population. Current methods of migraine treatment include lifestyle changes, pharmacologic, and minimally invasive techniques such as peripheral nerve stimulation (PNS) and pericranial nerve blocks (PNB).

Recent Findings

PNBs are used to treat and prevent migraines and involves injection of local anesthetics with or without corticosteroids. PNBs include the greater occipital, supraorbital, supratrochlear, lesser occipital, auriculotemporal, sphenopalantine ganglion, and cervical root nerve blocks. Of the PNBs, the most extensively studied is the greater occipital nerve block (GONB) which has been shown to be an efficacious treatment for migraines, trigeminal neuralgia, hemi-crania continua, and post-lumbar puncture, post-concussive, cluster, and cervicogenic headaches but not medication overuse and chronic tension type headaches.

Summary

In this review, we aim to summarize the recent literature on PNBs and their efficacy in the treatment of migraines including a brief discussion of peripheral nerve stimulation.

Minimally Invasive Nerve- and Muscle-Sparing Surgical Decompression for Occipital Neuralgia

BACKGROUND

Occipital neuralgia is a well-defined type of headache, and its treatment algorithm is still debated across medical specialties. From the analysis of the literature, it appears that surgical decompression of the occipital nerves is the most effective invasive approach to improve the quality of life of patients with occipital neuralgia refractory to medications. The authors describe here a minimally invasive nerve- and muscle-sparing technique to decompress the occipital nerves.

METHODS

The results in terms of reduction of migraine days per month, use of medications, pain evaluation, and decrease in Migraine Headache Index were analyzed by means of a retrospective chart review of 87 patients who underwent nerve- and muscle-sparing surgical decompression of the greater and lesser monolateral or bilateral occipital nerves in their institution and were followed up for at least 12 months. The surgical technique is described in detail.

RESULTS

Surgical decompression significantly reduced occipital neuralgia burden (at least 50% improvement) in 91% of patients, with 45% reporting a complete remission of occipital pain. Days with pain per month decreased by 80%, chronic background pain intensity decreased by 81%, and pain intensity during crisis decreased by 76%. Accordingly, drug use dropped by approximately 70%. Only minor complications were reported in four patients.

CONCLUSIONS

The described technique could contribute to and further support surgical decompression as the first option among the invasive approaches to treat occipital neuralgia. Results corroborate previous findings, adding a less-invasive, nerve- and muscle-sparing approach.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Fusion of the Greater and Suboccipital Nerves: A Case Report With Application to Patients With Occipital Neuralgia

Atypical presentations of occipital neuralgia might have an anatomical cause. Therefore, a better understanding of variant anatomy in this region can help physicians who treat such patients. During the dissection of the suboccipital region in an 83-year-old at-death male cadaver, an unusual finding was noted between the suboccipital and greater occipital nerves. No branches from this segment of the suboccipital nerve were identified. Therefore, initially, the suboccipital muscles were thought to be innervated not by the suboccipital nerve but rather by branches of the medial (greater occipital nerve) and lateral branches of the C2 dorsal ramus. However, with microdissection, these fibers were found to ascend with the medial branch of the C2 ramus (greater occipital nerve) and to distribute fibers to the rectus capitis minor and major and then continue with the greater occipital nerve to the skin over the occiput. No fibers from the suboccipital nerve traveled to the C2 spinal nerve or its lateral branch. The lateral part of the dorsal ramus of C2 innervated the obliquus capitis superior and obliquus capitis inferior. Additionally, a long slender branch from the lateral branch of the C2 dorsal ramus traveled medially to innervate the skin over the C2 spinous process. This case demonstrates that some fibers in the greater occipital nerve (C2), both cutaneous and motor, can be derived from the suboccipital nerve (C1). This information can help in diagnosing some patients with atypical presentations and can help better target all involved occipital nerves.

Magnetic resonance neurography of the head and neck: state of the art, anatomy, pathology and future perspectives

Magnetic resonance neurography allows for the selective visualization of peripheral nerves and is increasingly being investigated. Whereas in the past, the imaging of the extracranial cranial and occipital nerve branches was inadequate, more and more techniques are now available that do allow nerve imaging. This basic review provides an overview of the literature with current state of the art, anatomical landmarks and future perspectives. Furthermore, we illustrate the possibilities of the three-dimensional CRAnial Nerve Imaging (3D CRANI) MR-sequence by means of a few case studies.

Peripheral nerve blocks for headache disorders

Headache is a common neurological referral and a frequent cause for acute hospital admissions. Despite peripheral nerve blocks being widely used in headache and pain services to treat patients with headache disorders, there is no readily accessible resource with instructions for the delivery of peripheral nerve blocks. Here we provide a practical approach for administering peripheral nerve blocks and cover the current evidence base for such procedures in different headache disorders. We provide instructions and an audiovisual guide for administering greater and lesser occipital, supratrochlear, supraorbital and auriculotemporal nerves blocks, and give information on their adverse effects and potential complications. This information will provide a reference for headache practitioners when giving peripheral nerve blocks safely to people with headache.

Sihler's staining of the cutaneous nerves of the leg and its implications for sensory reconstruction

INTRODUCTION

This study aimed to reveal the entire cutaneous nerve distribution pattern of the leg and provide a morphological basis for sensory reconstruction during skin flap transplantation.

MATERIALS AND METHODS

Twelve adult cadavers were fixed with formalin, and the whole leg skin with subcutaneous fat was removed close to the muscle surface. The cutaneous nerves were visualized using modified Sihler's staining to reveal the distribution and innervation density of the cutaneous nerves.

RESULTS

The saphenous nerve innervated the anterior part, 82.2% of the upper-middle region of the lateral part of the anterolateral leg, and the upper 63.4% of the medial posterior leg. The superficial peroneal nerve innervated 90.1% of the lateral lower one-third of the anterolateral leg. The medial sural cutaneous nerve covered 26.4% of the posterior leg. The lateral sural cutaneous nerve covered 42.3% (approximately 28.6% overlap with the saphenous nerve) of the upper-middle region of the anterolateral and posterolateral leg. The number of branches differed between certain cutaneous nerves in the leg. Communications were observed between the arborizations of the four cutaneous nerves mentioned above. The highest density of primary and secondary nerve branches was observed in the upper one-third of the lateral posterior leg. The upper one-third of the posteromedial leg contained the highest density of intracutaneous nerve branches and highest number of total nerve branches.

CONCLUSIONS

These results may be used to map sensory regions when designing leg skin flaps for reconstruction surgery to obtain improved sensory recovery.

Anatomical analysis of antebrachial cutaneous nerve distribution pattern and its clinical implications for sensory reconstruction

This study aimed to reveal the distribution pattern of antebrachial cutaneous nerves and provide a morphological basis for sensory reconstruction during flap transplantation. Forearm specimens containing skin and subcutaneous fat were obtained from 24 upper extremities of 12 adult cadavers. Cutaneous nerves were visualized using modified Sihler's staining. Then the data was used to show the distribution pattern and innervation area of the forearm cutaneous nerve. The anterior branch of lateral antebrachial cutaneous nerve innervates 26% of the medial anterior forearm; the posterior branch innervates 38.21% of the lateral anterior forearm and 24.46% of the lateral posterior forearm. The anterior branch of medial antebrachial cutaneous nerve innervates the medial aspect of the forearm covering 27.67% of the anterior region; the posterior branch the lateral part of the forearm covering 7.67% and 34.75% of the anterior and posterior regions, respectively. The posterior antebrachial cutaneous nerve covers 41.04% of the posterior forearm. Coaptations were found between the branches of these cutaneous nerves. The relatively dense secondary nerve branches were found in the middle 1/3 of the lateral anterior forearm and the middle 1/3 of the medial posterior forearm. The relatively dense tertiary nerve branches were the middle 1/3 and lower 1/3 of the medial anterior forearm. The intradermal nerve branches were the relatively dense in the middle 1/3 of the medial anterior and lateral posterior forearm. The middle 1/3 of the medial and lateral forearm had the relatively dense total nerve branches. These results can be used sensory matching while designing forearm flaps for reconstruction surgeries to obtain improved recovery of sensory.