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The Anatomical Features of Denticulate Ligament in Human Fetuses

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The Anatomical Features of Denticulate Ligament in Human Fetuses Surgical and Radiologic Anatomy https://doi.org/10.1007/s00276-020-02456-0 ORIGINAL ARTICLE The anatomical features of denticulate ligament in human fetuses Özlem Elvan1 · Gülden Kayan2 · Mustafa Aktekin2 Received: 19 December 2019 / Accepted: 6 March 2020 © Springer-Verlag France SAS, part of Springer Nature 2020 Abstract Purpose To determine the morphological features of the denticulate ligament in fetal period. Methods Twelve formalin-fxed fetuses (six females and six males) with a mean gestational age of 27.0 ± 2.04 weeks (range between 25 and 32 weeks) were dissected to reveal morphological properties of the denticulate ligaments. Results 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 frst denticulate ligament process was always a large and prominent fbrous 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 den- ticulate 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 liga- ment 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. Conclusion Detailed morphological data about fetal denticulate ligament presented in this study provide signifcant informa- tion 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. Keywords Denticulate ligament · Dura mater · Fetus · Morphology · Spinal cord Introduction of processes, the apices of which are fxed at intervals to the arachnoid lined dural sac. Usually, 20–22 processes are The denticulate (ligamentum denticulatum, dentate liga- observed on each side [1, 7, 17, 22, 24]. The frst process of ment) ligament (DL) is a fat, fbrous sheet of pia running DL is as a thick band and attaches dura mater over the upper on both sides of the spinal cord extending out to anchor into rim of foramen magnum and behind the hypoglossal nerve. arachnoid and dura. It is located between the ventral and The DL stabilizes the spinal cord within the vertebral dorsal spinal roots, thus divides the vertebral canal into ante- canal [20, 23, 24]. In its defciency, spinal cord may become rior and posterior compartments. It extends from the upper instable and vulnerable to trauma and herniation [5]. How- rim of foramen magnum till the level of conus medullaris. ever, during certain surgical interventions, resection of DL Its medial border is continuous with the subpial connec- processes allows the surgeon to mobilize the spinal cord as tive tissue of the cord while its lateral border has a series well as to decrease the tension on the cord [6, 9, 21, 24]. On the other hand, to determine the midline for a safe entry, DL is an essential landmark [5]. Again in anterior, anterolateral * Özlem Elvan or posterior approaches to spinal cord, DL sectioning per- [email protected] mits manupulations on spinal cord [2, 10, 13, 14, 16]. 1 School of Health, Mersin University, Çiftlikköy Campus, Although DL has been studied in detail on adult cadav- Yenişehir, 33343 Mersin, Turkey ers so far, to our knowledge there is no such study in the 2 Department of Anatomy, School of Medicine, Mersin antenatal period. In this study, we aimed to determine the University, Mersin, Turkey Vol.:(0123456789)1 3 Surgical and Radiologic Anatomy morphological features of DL in fetal period to obtain data Fig. 1 Ventral view of the spi- which may be signifcant for related surgeries of spinal cord nal cord lower thoracic segment presenting double DL processes in early childhood. (asterisk) in T9–T10 level on the right side. DL process was absent in T8–T9 level on the Materials and methods same side. Arrows showing the distances between the attach- ment sites of DL process to Twelve formalin-fxed fetuses (six females and six males) the superior and inferior spinal without visible deformities of the vertebral column and spi- nerve roots at its dural sac nal cord with a mean gestational age of 27.00 ± 2.04 weeks (range between 25 and 32 weeks), present in the collection of Anatomy Department, School of Medicine, Mersin Uni- versity were evaluated (Table 1). Clinical Research Ethics Committee of Mersin University approved the study. Fetuses were placed in a prone position, a midline skin incision was performed, and paraspinous muscles were retracted laterally. After laminectomy, facets and pedicles were removed. A longitudinal midline incision was made over the posterior dura mater to expose the spinal cord and dorsal rootlets. It is observed that some DL processes were whereas numbers and percentages were used to express cat- extending between two consecutive dorsal rootlets. How- egorical parameters. ever, some other DL processes were located at the same level with the dorsal rootlets. Therefore, we detected DL processes after retracting the dorsal rootlets medially to Results evaluate them properly. Microdissections were applied under surgical microscope (Zeiss Opmi-Pico, Germany) and digital The DL was observed between the frst cervical and frst caliper (0.01 mm precision) was used for measurements. lumbar spinal cord segments. It was more prominent in Dissection and measurements were conducted under the cervical and upper thoracic levels than in the lower levels. same environmental conditions by the same researcher (ÖE After retracting the dorsal rootlets medially, it was possible as an anatomist). to observe DL more clearly. Its lateral border had free mar- Presence, process type (triangular/band-like) and number gin except where it forms a series of processes, the apices of of DL processes at each spinal level were recorded. The which were fxed at intervals to the arachnoid lined dural sac. distance between the attachment site of DL process to the There were 5 double DL processes within the same inter- superior spinal nerve root within the dural sac was recorded. val, while in 14 other intervals no DL process was observed Then, the distance between the attachment site of DL pro- which we recorded them as absent (Fig. 1, Table 2). cess and inferior spinal nerve root was measured (Fig. 1). The DL processes were attaching externally to dura mater Shapiro–Wilk Test was used for normality checks. Mini- in diferent forms; the typical form which has been defned in mum, maximum, mean values and standard deviation were all classical textbooks as ‘triangular-shaped extensions with used as descriptive statistics in continuous parameters, an apex attaching the dura mater’ was the most common in the present study as well. We also observed that the apex of Table 1 Demographic data of fetuses Table 2 Number of denticulate ligament processes Gestational age Foot length (mm) Gender (weeks) Number of fetus DL processes in pairs Unilateral DL processes Female Male at various levels (sides) 25 43.91 1 2 1 17 3 26 45.58 2 1 1 18 4 27 48.73 2 – 1 19 2 28 51.56 1 1 5 20 – 29 53.64 – 1 3 21 – 32 58.88 – 1 1 22 1 mm milimeter DL denticulate ligament 1 3 Surgical and Radiologic Anatomy Fig. 2 The DL processes were attaching to dura mater in two forms; triangular and band-like. Both triangular (arrows) and band-like DL processes (dotted arrow) were shown (a). Band-like DL processes were observed to be directed both downward (arrows) and upward Fig. 3 Dorsal view of the upper spinal cord segments. The frst DL (dotted arrow) and they were more frequently observed in lower tho- process was like a large and prominent fbrous band (asterisk) and racic levels (b) 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 (HC). Ventral rootlets of frst cervical nerve and vertebral artery (VA) were anterior to frst DL pro- triangle was not always reaching the dura mater, instead a cess while the spinal accessory nerve (arrow) was located posteriorly. thin, band-like process was arising from the apex and attach- A atlas, FM section of occipital bone at foramen magnum, JF jugular ing to dura mater. Moreover, this thin, band-like process was foramen directed downward to reach the dura mater in some fetuses, while it was in upward direction in some others (Fig. 2). In roots were measured bilaterally at each level (Table 3). cervical region between C1 and T1 spinal nerve roots, the Distance to upper nerve root was found to be 1.62 mm in DL processes were directly attaching dura mater forming cervical levels, while it was 2.05 mm in upper thoracic the triangular-shaped form in 60% of fetuses while in other and 2.32 mm in lower thoracic. At L1 level it was found 40% it was forming thin, band-like DL processes. However, 1.68 mm. Distances to lower nerve roots were similar to thin, band-like DL processes were more frequent in thoracic those of upper nerve roots in cervical and upper thoracic region (58%) than triangular-shaped ones (42%).
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