The optimization of intrathecal drug delivery procedures requires a deeper understanding of flow and transport in the spinal canal. Numerical modeling of drug dispersion is challenging due to the disparity in time scales: dispersion occurs over 1 hour, while cerebrospinal fluid pulsations driven by cardiac motion occur on a 1-second scale. Patient-specific predictions in clinical settings demand simplified descriptions that focus on drug-dispersion times, bypassing the rapid concentration oscillations caused by cyclic motion. A previously derived reduced-order model involving convective transport driven by mean Lagrangian drift is tested here through comparisons with MRI-informed direct numerical simulations (DNS) of drug dispersion in a cervical-canal model featuring nerve rootlets and denticulate ligaments. The comparisons demonstrate that the reduced model is able to describe precisely drug transport, enabling drug-dispersion predictions at a fraction of the computational cost involved in the DNS. Approximate descriptions assuming convective transport to be governed by the mean Eulerian velocity are found to significantly underpredict drug dispersion, highlighting the critical role of mean Lagrangian motion. Our results also confirm the substantial influence of microanatomical features on drug dispersion, consistent with earlier analyses. A key additional finding from the DNS is that molecular diffusion has a negligible impact on drug dispersion, with the mean drift of fluid particles primarily dictating the evolution of the drug distribution—an insight valuable for future modeling efforts.

Introduction Lesions in the cerebellomedullary angle, anterolateral aspect of lower brainstem, and anterior foramen magnum can be accessed through far lateral approach and extreme lateral infrajugular transcondylar exposure. Detailed anatomical knowledge of this region is of paramount importance to avoid untoward complications.Objectives Comprehensive anatomy of this microsurgical corridor is sparse. Our aim was to define the anatomy of this region with relevance to the surgical approach, which would enable the surgeon to navigate this region with ease during surgery.Materials and Methods Cadaveric dissection was performed with focus on the various anatomical structures, which are of relevance to the operating surgeon. The same was correlated with the computerized scan and magnetic resonance imaging brain findings and intraoperative findings. The observations are presented.Discussion Through the far lateral approach, the vagoaccessory triangle (VAT) and three subtriangles within it are exposed. Lateral boundary of the VAT is formed by the spinal accessory nerve, which follows a superolateral trajectory toward the jugular foramen. Medial boundary is formed by the medulla oblongata. Superior boundary is formed by the vagus nerve, which courses horizontally toward the jugular foramen. Rootlets of the hypoglossal nerve divide the VAT into infra-hypoglossal, supra-hypoglossal, and hypoglossal–hypoglossal subtriangles. The floor is formed by the inferior clivus, anterior foramen magnum, occipital condyle, and jugular tubercle. The roof is formed by the dura covering the lower part of the posterior fossa, biventral lobule, and tonsil of the cerebellum. The VAT contains three cisterns compartmentalized by three membranes, three nerves, and a fourth segment of vertebral artery (V4) with its three branches, in three subtriangles. Cisterns are the premedullary, lateral cerebellomedullary, and posterior cerebellomedullary. Membranes are the medial pontomedullary membrane, lateral pontomedullary membrane, and denticulate ligament. Nerves are the rootlets of hypoglossal, cranial accessory, and first cervical nerve. Posterior inferior cerebellar artery, anterior spinal artery, and posterior spinal artery are the three branches of V4.Conclusion Detailed knowledge of each anatomical structure and its relationship would enable the surgeon to operate safely within the corridors naturally present in this region.

The importance of optimizing intrathecal drug delivery is highlighted by its potential to improve patient health outcomes. Findings from previous computational studies, based on an individual or a small group, may not be applicable to the wider population due to substantial geometric variability. Our study aims to circumvent this problem by evaluating an individual’s cycle-averaged Lagrangian velocity field based on the geometry of their spinal subarachnoid space. It has been shown by Lawrence et al. (J Fluid Mech 861:679–720, 2019) that dominant physical mechanisms, such as steady streaming and Stokes drift, are key to facilitating mass transport within the spinal canal. In this study, we computationally modeled pulsatile cerebrospinal fluid flow fields and Lagrangian velocity field within the spinal subarachnoid space. Our findings highlight the essential role of minor structures, such as nerve roots, denticulate ligaments, and the wavy arachnoid membrane, in modulating flow and transport dynamics within the spinal subarachnoid space. We found that these structures can enhance fluid transport. We also emphasized the need for particle tracking in computational studies of mass transport within the spinal subarachnoid space. Our research illuminates the relationship between the geometry of the spinal canal and transport dynamics, characterized by a large upward cycle-averaged Lagrangian velocity zone in the wider region of the geometry, as opposed to a downward zone in the narrower region and areas close to the wall. This highlights the potential for optimizing intrathecal injection protocols by harnessing natural flow dynamics within the spinal canal.

In this article, we document the widespread presence of bony ridges in the neural canals of non-avian dinosaurs, including a wide diversity of sauropods, two theropods, a thyreophoran, and a hadrosaur. These structures are present only in the caudal vertebrae. They are anteroposteriorly elongate, found on the lateral walls of the canal, and vary in size and position both taxonomically and serially. Similar bony projections into the neural canal have been identified in extant teleosts, dipnoans, and urodelans, in which they are recognized as bony spinal cord supports. In most non-mammals, the dura mater that surrounds the spinal cord is fused to the periosteum of the neural canal, and the denticulate ligaments that support the spinal cord can pass through the dura and periosteum to anchor directly to bone. The function of these structures in dinosaurs remains uncertain, but in sauropods they might have stabilized the spinal cord during bilateral movement of the tail and use of the tail as a weapon. Of broader significance, this study emphasizes that important new discoveries at the gross anatomical level can continue to be made in part by closely examining previously overlooked features of known specimens.

The cranial cervical vertebral column carries a unique range of mobility with the addition of dorsal and ventral flexion and rotation. The denticulate ligaments provides support and protection of the spinal cord, but little is known of the adaption of this apparatus at the cranial cervical portion of the spinal cord. We present in this publication a new pair of ligaments in dogs that supports the spinal cord inside the vertebral canal at the level of the C1-C2 spinal segments.

Figure 1. Spinal cord of dog with emerging roots, and dura mater, divided in three parts (part of plate -Figure VII).⁴ Part I=cervical, Part II=thoracic, Part 3=lumbar, sacral, and tail bones. α=transit of root through the dura mater, β= union of the dura [dura mater] (C) with the thin meninx [pia mater] [denticulate ligament], I=extradural nodes developed from the convergence of several nerve fibers [spinal ganglia]

The common imaging features surgeons use to distinguish spinal meningiomas from spinal nerve sheath tumors on magnetic resonance (MR) scans include the presence of the “dural tail sign” on contrast-enhanced MR images, hypointensity of the lesion on T2 sequences, presence of calcifications, lack of extraspinal dumbbell extension, and the lack of cystic changes in the lesion. We highlight the rarely described finding–the “Gingko-Leaf” sign that is caused by the stretched denticulate ligament as it extends laterally, through the tumor, from the compressed spinal cord.

ABSTRACTPurpose:To describe the anatomical aspects of the cervical rootlets and to quantify the number of rootlets that compose C1 to T1.Methods:Twenty male rats were used in this study. The dorsal rootlets from C1 to T1 were analyzed. To study the ventral rootlets, the posterior root avulsion was performed using a microhook, allowing exposure of the ventral roots through manipulation of the denticulate ligament and arachnoid mater. The parameters analyzed were the number of ventral and dorsal rootlets by side and level.Results:The formation of the respective spinal nerve was observed in the spinal roots the union of the ventral and dorsal roots. In four animals the C1 spinal root had no dorsal and/or ventral contribution. There is no normal pattern of numerical normality of the dorsal and ventral rootlets. The average number of fascicles per root was 4.08, with a slight superiority on the left side. There was a slight superiority of the dorsal rootlets compared to the ventral rootlets.Conclusions:This investigation was the first to study cervical rootlets in rats. In 20% of the sample studied, the dorsal root of C1 was absent mainly on the left side. There is a nonlinear numerical increase from C1 to T1 in the rootlets. There is a numerical predominance of cervical fascicles on the left side, confronting several studies related to the functional predominance of right laterality, requiring new studies that correlate these variables.

Objective. To analyze the outcomes of posterior approach in the surgery of intradural extramedullary meningiomas located ventrally and dorsally in relation to the spinal cord denticulate ligaments.Material and Methods. The study included 29 patients with spinal intradural meningiomas operated on using posterior approach. Patients were divided depending on the tumor location relative to the denticulate ligaments into ventral (n = 13) and dorsal (n = 16) groups. The surgery duration, the degree of tumor resection, clinical outcomes, the presence and nature of complications, and the frequency of recurrence were assessed.Results. The average follow-up period was 29 (6 to 61) months. Total tumor removal was performed in 93.1 % of cases: 11 cases (84.6 %) in ventral group and 16 cases (100.0 %) in dorsal group. The average duration of surgery was 136 minutes for dorsal meningiomas and 181 minutes for ventral meningiomas (p < 0.05). Complications in the form of CSF leakage were registered in two patients (6.9 %). In 11 (84.6 %) patients with ventral meningiomas and 15 (93.7 %) patients with dorsal meningiomas, an improvement or preservation of neurological functions at the pre-surgery level was observed. Recurrences were observed in two patients (6.9 %).Conclusion. Patients with spinal meningiomas have a favorable neurological outcome and a low recurrence rate. Surgery is more complicated in patients with ventral meningiomas. In most cases, unilateral posterior approach is applicable for both ventral and dorsal meningiomas.

Cauda equina biopsy as a tool in the diagnosis of malignant tumors

Dural arteriovenous fistulae at the craniocervical junction are rare. When present together with spinal and cranial venous reflux they can have an aggressive natural history with hemorrhage or progressive myelopathy from venous congestion. In this operative video we demonstrate key steps in the surgical ligation of a dural arteriovenous fistula supplied by meningeal branches of the V4 segment of the vertebral artery. Informed consent was obtained. The patient was positioned prone with chin tucked. Utilizing a midline suboccipital craniotomy and removal of the arch of C1, the vertebral artery was identified at its V4 segment at it transitions from extra to intradural. The video illustrates how a midline approach can be used to access this lesion and a far lateral approach is not required to access the vertebral artery and its dural branches at the craniocervical junction. Division of the denticulate ligaments and mobilization of the spinal accessory nerve allows visualization of the proximal portion of the draining vein. Important anatomy in this region is demonstrated. The critical use of indocyanine green (ICG) dye is demonstrated as the first 2 clip applications were not proximal enough to obliterate the proximal draining vein and persistent early venous reflux was still seen on ICG. The importance of access to and obliteration of the proximal draining vein is shown. An intraoperative ICG and postoperative angiogram demonstrates complete occlusion of the dural arteriovenous fistula. In this case the patient had minor sensory deficits postoperatively which were resolved by 6 wk postoperatively.

To determine the morphological features of the denticulate ligament in fetal period. Twelve formalin-fixed fetuses (six females and six males) with a mean gestational age of 27.0 ± 2.04weeks (range between 25 and 32weeks) were dissected to reveal morphological properties of the denticulate ligaments. Denticulate ligament was observed as a continuous ligament extending throughout the length of spinal cord in all fetuses. It separated the vertebral canal into two as anterior and posterior parts and was anchored to the dura mater on either side of the spinal cord with mostly triangular processes as well as thin band-like extensions. The first denticulate ligament process was always a large and prominent fibrous band and was arising from the spinal cord surface, extending in an oblique direction upward to the anterolateral rim of foramen magnum, below and posterior to the hypoglossal canal. The last denticulate ligament process was observed either in the T11-12 (2 sides, 8%), T12-L1 (15 sides, 62%) or L1-2 (7 sides, 30%) and all were band-like processes. At certain spinal cord levels, denticulate ligament had no processes to attach duramater while in some other fetuses double denticulate ligament processes were detected within the same interval. The distance between the denticulate ligament process and the superior spinal nerve root and the distance between the denticulate ligament process and the inferior spinal nerve root were measured at each spinal level. This distance was found to be increased from upper to lower levels of the spine. Detailed morphological data about fetal denticulate ligament presented in this study provide significant information which may be essential during several surgical interventions performed in early postnatal period and childhood focusing on the spinal cord, spinal nerve roots and meningeal structures.

Continuous measurements and computation of absolute metrics of cervical subarachnoid space (CSS) and spinal cord (SC) geometries proposed are based on in vivo magnetic resonance imaging and 3D reconstruction. The aim of the study is to offer a new methodology to continuously characterize and to quantify the detailed morphology of the CSS and the cervical SC in 3D for healthy subjects in both neutral supine and flexion. To the best of our knowledge, no study provides a morphological quantification by absolute indices based on the 3D reconstruction of SC and CSS thanks to in vivo magnetic resonance imaging. Moreover, no study provides a continuous description of the geometries. Absolute indices of SC (cross-sectional area, compression ratio, position in the canal, length) and of CSS (cross-sectional area, occupational ratio, lengths) were computed by measures from 3D semi-automatic reconstructions of high resolution in vivo magnetic resonance images (3D T2-SPACE sequence) on healthy subjects (N = 11) for two postures: supine neutral and flexion neck positions. The variability induced by the semi-automatic reconstruction and by the landmarks positioning were investigated by preliminary sensitivity analyses. Inter and intra-variability were also quantified on a randomly chosen part of our population (N = 5). The length and cross-sectional area of SC are significantly different (P < 0.05) in flexion compared with neutral neck position. Spinal cord stays centered in the canal for both postures. However, the cross-sectional area of CSS is submitted to low variation after C3 vertebra for both postures. Occupational ratio (OR) and compression ratio (CR) after C3 are significantly lower in flexion. This study presented interpretations of morphological measures: (1) left-right stability (described by the Left-Right eccentricity index) ensured by the denticulate ligaments and the nerve roots attached to the dural sheaths, (2) a Poisson effect of the SC was partially notified through its axial (antero-posterior [AP] diameter, OR, CR) and its longitudinal geometrical descriptions (length of spinal cord [LSC]). Such morphological data can be useful for geometrical finite element modeling and could now be used to compare with injured or symptomatic subjects. 3.

For small and lateral lesions, in order to avoid postoperative sequelae related to dorso-median myelotomy, we propose to describe the use of a ventrolateral approach for intramedullary lesions. Performing this approach entails that the denticulate ligament is cut from its dural attachment and retracted. Rotation of the spinal cord must be achieved with great caution and under electrophysiological monitoring. After pia mater incision, hydrodissection is useful to gently dissect the cavernoma and promote a cleavage plane. In the case of lateral intramedullary lesions, using this approach maximized the absence of postoperative deficit.

SynopsisBirds are diverse and agile vertebrates capable of aerial, terrestrial, aquatic, and arboreal locomotion. Evidence suggests that birds possess a novel balance sensing organ in the lumbosacral spinal canal, a structure referred to as the “lumbosacral organ” (LSO), which may contribute to their locomotor agility and evolutionary success. The mechanosensing mechanism of this organ remains unclear. Here we quantify the 3D anatomy of the lumbosacral region of the common quail, focusing on establishing the geometric and biomechanical properties relevant to potential mechanosensing functions. We combine digital and classic dissection to create a 3D anatomical model of the quail LSO and estimate the capacity for displacement and deformation of the soft tissues. We observe a hammock-like network of denticulate ligaments supporting the lumbosacral spinal cord, with a close association between the accessory lobes and ligamentous intersections. The relatively dense glycogen body has the potential to apply loads sufficient to pre-stress denticulate ligaments, enabling external accelerations to excite tuned oscillations in the LSO soft tissue, leading to strain-based mechanosensing in the accessory lobe neurons. Considering these anatomical features together, the structure of the LSO is reminiscent of a mass-spring-based accelerometer.

The arachnoid membranes' anatomy is a controversial topic in the literature, and the rhomboid membrane at the craniovertebral junction is an element of this system that has been described poorly. Hence, the objective of our study was to examine this membrane's anatomy and histology. A total of 45 fresh formalin-fixed human cadaveric heads were examined, and anatomic dissections and histologic examinations using standard staining methods were performed. The membrane was found to be a constant structure. It has a rhomboid shape and is located on the medulla oblongata and upper cervical spine's ventral surface within the subarachnoid space. Its average craniocaudal length is 49 mm and the short axis is 26 mm. The cranial apex is attached to the vertebral arteries' junction, and the caudal apex reaches the level of C4. The lateral apices are attached to the dura mater at the level of the denticulate ligament's second insertion. The C1 spinal nerves perforate the membrane, while the C2 roots are located dorsal to it. The membrane is attached strongly to the underlying pia mater. Histologically, it has a typical arachnoid structure, in which its adhesions to the vertebral arteries as well as to the pia mater could be verified histologically. This is the first detailed examination of the rhomboid membrane. Our results suggest that the membrane serves a valve-like function between the spinal and cranial subarachnoid spaces. Based on our findings, further hydrodynamic studies should clarify the membrane's physiological role. Clin. Anat. 32:56-65, 2019. © 2019 Wiley Periodicals, Inc.

The goal in this study was to describe the overall organization of the spinal arachnoid mater and spinal subarachnoid space (SSAS) as well as its relationship with surrounding structures, in order to highlight spinal cord arachnoid cisterns. Fifteen spinal cords were extracted from embalmed adult cadavers. The organization of the spinal cord arachnoid and SSAS was described via macroscopic observations, optical microscopic views, and scanning electron microscope (SEM) studies. Gelatin injections were also performed to study separated dorsal subarachnoid compartments. Compartmentalization of SSAS was studied on 3 levels of axial sections. On an axial section passing through the tips of the denticulate ligament anchored to the dura, 3 subarachnoid cisterns were observed: 2 dorsolateral and 1 ventral. On an axial section passing through dural exit/entrance of rootlets, 5 subarachnoid cisterns were observed: 2 dorsolateral, 2 lateral formed by dorsal and ventral rootlets, and 1 ventral. On an axial section passing between the two previous ones, only 1 subarachnoid cistern was observed around the spinal cord. This compartmentalization resulted in the anatomical description of 3 elements: the median dorsal septum, the arachnoid anchorage to the tip of the denticulate ligament, and the arachnoid anchorage to the dural exit/entrance of rootlets. The median dorsal septum already separated dorsal left and right subarachnoid spaces and was described from C1 level to 3 cm above the conus medullaris. This septum was anchored to the dorsal septal vein. No discontinuation was observed in the median dorsal arachnoid septum. At the entrance point of dorsal rootlets in the spinal cord, arachnoid trabeculations were described. Using the SEM, numerous arachnoid adhesions between the ventral surface of the dorsal rootlets and the pia mater over the spinal cord were observed. At the ventral part of the SSAS, no septum was found, but some arachnoid trabeculations between the arachnoid and the pia mater were present and more frequent than in the dorsal part. Laterally, arachnoid was firmly anchored to the denticulate ligaments' fixation at dural points, and dural exit/entrance of rootlets made a fibrous ring of arachnoidodural adhesions. At the level of the cauda equina, the arachnoid mater surrounded all rootlets together-as a sac and not individually. Arachnoid cisterns are organized on each side of a median dorsal septum and compartmentalized in relation with the attachments of denticulate ligament and exit/entrance of rootlets.

Caudal part of the human spinal cord from the dorsal side. Lig. dent. = denticulate ligament. Dissection of the Author.

OBJECTIVESpinal meningiomas (sMNGs) are relatively rare in comparison to intracranial MNGs. sMNGs localized anterior to the denticulate ligament (aMNGs) represent a surgically challenging subgroup. A high perioperative complication rate due to the need for complex surgical approaches has been described. In the present study, the authors report on their surgical experience that involves two institutions in which 207 patients underwent surgery for sMNGs. Special focus was placed on patients with aMNGs that were treated via a unilateral posterior approach (ULPA).METHODSBetween 2005 and 2017, 207 patients underwent resection of sMNGs at one of two institutions. The following characteristics were assessed: tumor size and localization, surgical approach, duration of surgery, grade of resection, peri- and postoperative complication rates, and neurological outcome. Data were compared between the subgroups of patients according to the lesion's relationship to the denticulate ligament and to surgical approach.RESULTSThe authors identified 48 patients with aMNGs, 86 patients with lateral MNGs, and 76 patients with posterior MNGs (pMNGs). Overall, 66.6% of aMNGs and 64% of pMNGs were reached via a ULPA. aMNGs that were approached via a ULPA showed reduced duration of surgery (131 vs 224 minutes, p < 0.0001) and had surgical complication rates and neurological outcomes comparable to those of lesions that were approached via a bilateral approach. No significant differences in complication rate, outcomes, and extent of resection were seen between aMNGs and pMNGs.CONCLUSIONSThe duration of surgery, extent of resection, and outcomes are comparable between aMNGs and pMNGs when removed via a ULPA. Thus, ULPA represents a safe route to achieve a gross-total resection, even in cases of aMNG.

The denticulate ligament – Tensile characterisation and finite element micro-scale model of the structure stabilising spinal cord