Which among the following is remnant of notochord?
Correct Answer: Nucleus pulposus
Description: Ans. B. Nucleus pulposus.The intervertebral disks consist of an outer core of fibrocartilage, the annulus fibrosus, and an inner part-the nucleus pulposus that develop from the notochord. Herniation of the nucleus pulposus is usually posterolateral where it can compress spinal nerve at the intervertebral foramen.# Notochord induces overlying ectoderm to differentiate into neuroectoderm and form the neural plate.# Neural plate gives rise to the neural tube and neural crest cells. Notochord becomes nucleus pulposus of the intervertebral disc in adults.# Alar plate (dorsal): sensory and Basal plate (ventral): motor = Same orientation as spinal cord.Embryological Derivatives:a)Surface ectodermAdenohypophysis, lens of eye, epithelial linings, epidermis.b)NeuroectodermNeurohypophysis, CNS neurons, oligodendrocytes, astrocytes,pineal gland.c)Neural crest0Autonomic Nervous System, Dorsal root ganglia (DR6), melanocytes, chromaffin cells of adrenal medulla, enterochromaffin cells, pia matter, celiac ganglion, Schwann cells odontoblasts, parafollicular 'C cells of thyroid.d)MesodermDura connective tissue, muscle bone, cardiovascular structures, lymphaties, blood, urogenital structures, macroglia and serous lining of body cavities, spleen, adrenal cortex.e)EndodermGut tube epithelium and derivatives (e.g., lungs, liver, pancreas, thymus, thyroid, parathyroid).f)NotochordInduces ectoderm to form neuroetoderm (neural plate). Its postnatal derivative is nucleus pulposus of the intervertebral disc.Additional Educational points:Chordoma# rare and accounts for 4% of malignant (locally invasive) bone tumors.# Origin from the primitive notochord.# Males more frequently than females.# Seen between 30 and 80 years of age.# Site:- 50% sacrococcygeal in origin,- 37% arise in the sphenoccipital area (clivus), and- remainder from vertebral bodies of the cervical or lumbar spine.- The cranial lesions are seen in a younger age group and carry a poor prognosis.# C/f: Because of the slow tumor growth, pain may not occur early, but constipation can be an early symptom that results from pressure on the rectum.# On X-ray: centrally located lytic lesion with minimal sclerotic response at the periphery and may show slight matrix calcification, as in a chondrosarcoma.# If the sacrum is involved, the lesion is seen usually in the lower three sacral segments and presents as an extracortical lobulated mass both in front and behind the sacrum.# It is best to image this tumor with CT or MRI,# Microscopically, nests or cords of cells, sprinkled in a sea of mucinous tissue, give an appearance similar to low-grade chondrosarcoma. In most cases, large vacuolated cells appear like a signet ring and are referred to as physaliferous cells.# Rx: Surgical excision.
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