Embryology Flashcards
Where is neuronal tissues derived from?
Ectoderm
Notochord is formed from the ___ layer.
Mesoderm
What does the notochord do?
Induces the overlying neuroectoderm to differentiate into the neural plate
When does the neuroectoderm differentiate into the neural plate?
18 days gestation
What does the notochord become?
Intervertebral discs
When does the the neural plate invaginates to form the neural tube?
3rd-5th weeks of gestation
Neurulation in two phases
Primary neurulation (dorsal induction)
Secondary neurulation (caudal induction)
Defects of primary or secondary neurulation lead to what issues?
Cortical and spinal cord malformations
What does the neural tube develop into?
Brain
Brainstem
Spinal cord
Preganglionic sympathetic neurons
What factors can cause neural tube defects (especially spina bifida)?
Folate/B12 deficiency
Valproic acid
Carbamazepine
Abnormal genetics
What becomes motor neurons of the cranial nerve and anterior horn gray matter?
Basal plate (ventral) of the neural tube
Week 10
What becomes posterior horn gray matter and sensory neurons?
Alar plate (dorsal) of neural tube
Week 10
What leads to the growth of the PNS?
Neural crest cells
What do neural crest cells become?
Schwann cells
Neuroglial cells
Parasympathetic and postganglionic sympathetic fibers
Melanocytes
Pia and arachnoid
Thyroid
Teeth
Three primary vesicles of the developing brain
Week 4
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
What does the prosencephalon develop into?
Telencephalon
Diencephalon
What does the rhombencephalon develop into?
Metencephalon
Myelencephalon
Five secondary vesicles
Week 5
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
Telencephalon develops into the ___.
Cerebral hemispheres
Basal ganglia
Hippocampus
Amygdala
Diencephalon develops into the ___.
Thalamus
Hypothalamus
Retina
Mesencephalon develops into the ___.
Midbrain
Metencephalon develops into the ___.
Pons
Cerebellum
Myencephalon develops into the ___.
Medulla
What are the 6 layers of the neocortex?
Molecular layer (most superficial)
External granular layer
External pyramidal layer
Internal granular layer
Internal pyramidal layer
Multiform layer (deepest layer)
When does in-utero myelination start?
14 weeks
When does the majority of in-utero myelination occur?
3rd trimester
When do subcortical U fibers myelinate?
8 months
Do not finish until the second decade of life
When is peripheral myelination completed?
3-5 years
Which myelinates first?
Motor or sensory roots?
Motor
What is a dermal sinus tract?
Tract of squamous epithelium that travels from the skin to the dura of the spinal cord
Where are dermal sinus tracts most often found?
Midline and in the lumbar/lumbosacral region
What tumors are associated with dermoid sinuses?
Dermoid or epidermoid tumors
What causes dermal sinuses?
Failure of differentiation between cutaneous ectoderm and neuroectoderm in the 4th week of development
What is the presentation of a congenital dermal sinus?
Recurrent meningitis (bacterial portal)
Tethered cord
Cord compression
What is the treatment for a dermal sinus?
Complete excision
What is craniorachischisis?
Complete failure of neural tube formation leading to both anencephaly and extensive spina bifida
A failure of anterior neural tube closure
Anencephaly
Defect of cranial mesoderm development which leads to a skull defect with protrusion of both meninges and brain
Encephalocele
What disease in an encephalocele associated with?
Meckel-Gruber syndrome.
A pathological opening of the vertebral column in which meninges protrudes through the skeletal defect without neurologic tissue outside the spinal cord
Meningocele
Incomplete closure of the caudal neural tube
Meninges and spinal cord are both herniated through the defect in a covered membrane
Myelomeningocele
Myelomeningocele without spinal contents covered by a membrane is called:
Myeloschisis
Incomplete closure of the vertebrae with an overlying tuft of hair or dimple
Generally asymptomatic
Spina bifida occulta
Defects of spinal cord development
Imaging show longitudinal duplication/splitting and tethering of the spinal cord
Diastematomyelia
Chiari I
Downward displacement of the cerebellar tonsils at least 5 mm beyond the foramen magnum
Chiari II
Displacement of the cerebellar tonsils as well as the brainstem
Patients with Chiari II can also have a ____ and at risk for ____.
Myelomeningocele
Hydrocephalous
Chiari malformation associated with syringomyelia:
I and II
Symptoms of a syringomyelia:
Loss of pain in a “cape-like” distribution
Arm weakness
Cause of symptoms with a syringomyelia:
Damage of the crossing spinothalamic fibers
Damaged anterior horn cells
Cortical malformations: Disorders of cell proliferation/apoptosis
Focal cortical dysplasia with balloon cells
Megalencephalic
Microcephaly
Cortical malformations:
Disorders of cell migration
Lissencephaly
Pachygyria
Heterotopia
A complete absence of cortical sulci results in a smooth, cerebral cortex
Lissencephaly
Most common genetic defect causing lissencephaly
LIS-1 or XLIS genes
Thickened gyri with lose of normal interdigitation of gray matter
Pachygyria
Ectopic position of neurons, common epilepsy focus
Heterotopia
What gene is associated with periventricular Nodular Heterotopia?
X-linked dominant FLNA (filamin A) mutations
Cortical malformations:
Disorders of cortical organization
Polymicrogyria
Schizencephaly
What disease often occurs with polymicrogyria?
Zellweger’s syndrome
Caused by disruption of the cortical mantle leading to a cleft in the cortex that extends from the lateral ventricle
Schizencephaly
Failure of the prosencephalon to develop midline structures
Holoprosencephaly
Possible structural findings in holoprosencephaly
Midline facial anomalies (cyclopia)
Absence of the olfactory system
Agenesis of the corpus callosum
Fused thalamus
Atypical ventricular structure
Most common genetic cause of holoprosencephaly
Trisomy 13
What is the structural presentation of septo-optic dysplasia (DeMorsier syndrome)?
Secondary symptoms to optic nerve hypoplasia
Absence of olfactory bulbs and tracts
Pituitary gland dysfunction
Absence of the septum pellucidum
Genetic disorder that presents with cerebellar dysfunction, hyperpnea, and intellectual delay
Agenesis/underdevelopment of the vermis
Joubert syndrome
“Molar tooth” sign
Joubert syndrome
Agenesis of the cerebellar vermis, cystic dilation of the fourth ventricle, and elevation of the tentorium
Dandy-Walker malformation
Arachnoid cyst is due to what abnormal formation?
Abnormal formation of leptomeninges
In what instance can an arachnoid cysts appear “box shaped”?
If it’s located in the sylvian fissure
What is a porencephalic cyst due to?
Early intrauterine vascular injury or infection
What is the difference between a porencephalic cyst and schizencephaly, structurally?
Porencephalic cyst is smooth-walled and not lined by cortex
Large central cyst with a lack of cortical tissue in anterior circulation-supplied areas
Hydranencephaly
What structures tend to be preserved in hydranencephaly?
Cerebellum
Midbrain
Basal ganglia
What causes hydranencephaly?
Severe hypoxic/ischemic insult early in development
Unilateral enlargement of cortex parenchyma with thickened or duplicated grey matter
Hemimegaloencephaly
Clinical findings in hemimegalencephaly
Epilepsy, intellectual disability, and hemiparesis
What is the treatment for medically refractory epilepsy in setting of hemimegalencephaly?
Hemispherectomy
What aqueduct is most commonly blocked in congenital aqueductal stenosis?
Aqueduct of Sylvius
What are the symptoms of aqueductal stenosis?
Headache, nausea, visual disturbances, altered mental status
Enlargement of head size in first year of life
What is the treatment for aqueductal stenosis?
Ventriculo-peritoneal shunt or ventriculostomy
