Vertebral Column Development - Anatomy 01 - 2025-01-22

VERTEBRAL COLUMN: DEVELOPMENT & CONGENITAL DISEASE Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s...

VERTEBRAL COLUMN: DEVELOPMENT & CONGENITAL DISEASE Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: To relate the stages of vertebral development to developmental errors and associated clinical manifestations Outline: Outcomes: Describe the development of the notochord and how the notochord contributes to the human vertebral column development Rise of the vertebrates Describe the process of vertebral development from its somite origin, its segmentation, and the 3 stages of morphological formation and growth (mesenchymatous, cartilaginous, and osseus) Stages of vertebral development and Identify the different congenital malformations of the vertebral column developmental errors presented in this lecture, and describe how they occur from a given stage of vertebral development and how they reflect age Identify and describe the different vertebral elements, what vertebral Vertebral elements features they contribute to, how they differ between vertebral regions, and how this relates to Hox gene expression in a general sense Growth of the vertebral column Chordates & vertebrates Chordates: Have a notochord at some stage Hollow dorsal nerve tube Pharynx Ventral heart Brain Tail beyond the anus Segmentation Vertebrates: Have a vertebral column Paired sense organs Thyroid and pituitary glands Vertebral column develops in responds to notochord signals von Baer’s Laws of embryology: “General features appear first” Notochord before vertebral column Most adult chordates look similar to a barnacle/plant Don’t possess anything like a vertebral column Vertebrates: Those who refused to grow up Juvenile chordates do have vertebrate characteristics A head Spinal cord (hollow dorsal nerve tube) Tail that extends beyond the anus Notochord acts as a stiffening rod for muscle attachment Segmented muscles act on either side Allows alternating side to side movements (different to a worm) Notochord and tail are lost when creature attaches to a rock and becomes an adult Vertebrates: Those who refused to grow up What do they look like, post-rock adhesion?  But what if they didn’t stick themselves to rocks? They keep their juvenile characteristics Neotony: Evolutionary process where juvenile characteristics are retained in the adult and passed on No metamorphosis Vertebral development is a 3 step process: 1) Mesenchymatous, 2) cartilaginous, 3) osseus Mesenchymatous stage (4-6 weeks) Transverse view Somites are PARAXIAL mesoderm! Sclerotome cells of somites migrate: 1. Perinotochordal sheath (not segmented) 2. Neural arch 3. Costal element Coronal view Body wall vessels from aorta form between somites (tissue is less dense there) At the level of the developing vertebral bodies Vertebral segmentation (or somite ‘re-segmentation’) is driven by gene expression & blood supply These terms just refer to each vertebrae being derived from 2 somites Location of a vertebral segment = Intervertebral disc location / where nerve roots exit from Mesenchymatous stage (4-6 weeks) Coronal view Sclerotome cells of somites migrate: 1. Perinotochordal sheath (not segmented) 2. Neural arch 3. Costal element Myotome Perinotochordal cells near these vessels have better nutrition, thus: Grow larger and will form hyaline cartilage which become  vertebral bodies (VBs) Myotome VBs form in line with the gap between adjacent somites (same as BVs…) Each vertebra is formed from parts of 2 adjacent somites = intersegmental Segment is where the movement happens, where the nerve roots emerge from Mesenchymatous stage (4-6 weeks) Myotomes of somites are segmental: Coronal view 1 intervertebral muscle is from 1 somite The mixed spinal nerve exits the vertebral canal at the level of the intervertebral disc = Myotome Notochord squeezed into the zone between developing VBs Happens in line with each somite Thus, each segment centres around an intervertebral disc  Transverse view Cartilaginous stage (6-9 weeks) Mesenchymatous model of vertebrae in place already  Paired primary centres of chondrification start to form as: 1. Centrum 2. Neural arches 3. Costal Mesenchyme gradually replaced by hyaline cartilage Light blue in the fetal slides Coronal view Region where intervertebral discs will develop: In line with each somite Segments and somites are aligned Fibrocartilage forms the annulus fibrosus (fibrous circle) Purple in the fetal slides Annulus fibrosus forms around the notochordal remnant: Nucleus pulposus Remnant because it is no longer a ‘rod’, but a segmented collection of cells along the developing vertebral column What happens if something goes wrong? Cartilage centres are paired, what happens if one fails to form? The other doesn’t stop Develop vertebral asymmetry: Hemivertebrae Can cause structural scoliosis Osseous stage (8-10 weeks GA - ~6-8 years) Transverse view Cartilaginous model of vertebra in place already  Primary centres of ossification appear: 1. Centrum (UNPAIRED) 2. Neural arches 3. Costal Coronal view Continues to grow beyond birth 16mm @8w ga embryo - ~50cm at birth Allows expansion of spinal cord and further VC growth Osseous stage (8-10 weeks GA - ~6-8 years) Transverse view 1. Centrum (UNPAIRED) 2. Neural arches 3. Costal Bone grows but cartilage growth plates continue to separate the ossification centres (these plates don’t ossify until ~6-8y.o.a) Coronal view 1. Inter-laminar cartilage 2. Neuro-central cartilage This makes the primary ossification stage the longest developmental stage Costal centres either fuse with the rest of the vertebra or become ribs and develop joints (thorax only) What happens if there are too few or too many notochordal cells? Answers on slides to follow  Block vertebra Ossification and the notochord: Block vertebra: Ossification can obliterate the disc if… Too few notochordal cells remain Relate to IVD formation Failure of segmentation (begins during mesenchymal and cartilaginous stages, but presents morphologically in osseous phase)  Butterfly vertebra Ossification and the notochord: Butterfly vertebra: Ossification of the centrum is retarded if… Too many notochordal cells remain Notochord seems to inhibit bone deposition Too much nucleus pulposus in IVD… Failure of formation Prof. Parizel Chest X-ray seminar  Vertebral elements Each ossification centre forms a vertebral element 1. Centrum element Central portion of vertebral bodies Does NOT make the whole vertebral body 2. Neural arch element Dorsal arch surrounds spinal cord Zygapophyseal joints, mammillary processes Contributes to lateral aspect of vertebral body 3. Costal element Form ribs in the thorax, but in different regions it forms different features of respective vertebra Note the gap between costal and neural elements Are all transverse processes from the same elements? No! You can see this happening in the transverse fetal slides Hox genes Hox genes control body segment features Embryonic rodent study A: Schematic of Hox gene expression in different regions B: Loss of Hox10 caused additional ribs to develop in the lumbar and sacral regions A Thoracic-isation of the lumbar vertebrae C: Gain in Hox10 gene created lumbar vertebrae in the thorax Lumbar-isation of the thoracic vertebrae Sternum not formed by sclerotome, but instead by the somatopleure (LP-M) thus still present Growth of the vertebral column At birth: Centrum and neural primary ossification centres still separated by cartilage growth plates 1. Interlaminar 2. Neurocentral By 6-8 years the above growth plates close, but the Vert. Body cartilage endplates are still ‘open’ At puberty secondary centres of ossification appear: 1. Spinous process 2. Transverse and mammillary processes 3. Ring epiphysis (osseus ring within periphery of endplate) Bone deposited towards Vert.Body side of end plates Processes continue to grow longer Growth of the vertebral column Vert.Bodies can continue to grow taller due to the ring epiphysis Not much, but there are 24 of them above the sacrum… Once closed (~20yoa), called ring APOphysis All epiphyses close at adulthood but surface remodelling can still continue (impacts surface area and shape, not height) Prepubescent late teens late teens  All are normal  University of Bologna: Note the epiphyseal (AKA growth) plates University of Bologna: Note the epiphyseal (AKA growth) plates