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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}} {{Alison}}
|QuestionAuthor= {{YD}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Embryology
|MainCategory=Embryology
Line 21: Line 21:
|MainCategory=Embryology
|MainCategory=Embryology
|SubCategory=Neurology
|SubCategory=Neurology
|Prompt=A 23-year-old male is referred to a neurologist for evaluation of a progressively worsening vertigo and hearing loss that started almost 4 months ago. A brain MRI showed bilateral cerebello-pontine angle masses. Which of the following is the most likely embryological origin of the cells from which this patient’s masses arose?
|Prompt=A 23-year-old man is referred to a neurologist for the evaluation of a progressively worsening vertigo and hearing loss in both ears for the past 4 months. The patient has no past medical history. The patient has no significant past medical history. He denies allergies, smoking, alcohol intake, or use of illicit drugs. A brain MRI is performed and shows bilateral cerebellopontine angle tumors. Which of the following is the most likely embryological origin of the cells from which this patient’s masses arose?
|Explanation=The patient presents with bilateral masses, compressing [[CN VIII]], which results in hearing loss and [[vertigo]]. The bilateral nature of the masses, the age of the patient, and the involvement of the [[CN VIII]] are all characteristic of [[neurofibromatosis type II]]. Hence, the masses are more likely bilateral vestibular [[schwannoma]].  The embryological origin of schwannomas is the [[neural crest]].
|Explanation=Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disorder characterized by its predisposition to the development of tumors, namely multiple schwannomas, meningiomas, and ependymomas. In contrast to neurofibromatosis type 1 (NF1), NF2 is not classically associated with the development of neurofibromas. The hallmark of NF2 is the development of bilateral vestibular schwannomas. Patients typically present with hearing loss, tinnitus, and/or vertigo. The presence of bilateral cerebellopontine angle tumors, the age of the patient, and and the clinical involvement of the [[CN VIII]] are all characteristic of NF2. The embryological origin of schwann cells, which abnormally proliferate into bilateral schwannomas in NF2, is the [[neural crest]]. Schwann cells are highly plastic, neural crest-derived cells that ensheath the peripheral nerves. Neural crest cells migrate between the ectroderm and the neural tube during development and gives rise to the PNS (including celiac and dorsal root ganglia, cranial nerves, schwann cells), autonomic nervous system, pia and arachnoid mater, melanocytes, chromaffin cells of the adrenal medulla, parafollicular C cells of the thyroid gland, bones of the skull and facial cartilage, odontoblasts, ciliary body of the eye, and the aorticopulmonary septum of the developing heart.
|AnswerA=Mesoderm
|AnswerA=Mesoderm
|AnswerAExp=The [[mesoderm]] gives rise to:
|AnswerAExp=The [[mesoderm]] gives rise to muscle, bone, connective tissue, spleen, kidneys, adrenal cortex, cardiovascular and lymphatic structures, wall of gut tube, serious linings of body cavities, vagina, ovaries, testes, and dermis.
 
-  [[Mesenchyme]] (connective tissue)
 
-  [[Mesothelium]]
 
-  Non-epithelial blood cells and coelomocytes
 
-  [[Muscles]]
 
-  Septa
 
-  Mesenteries
 
-  Part of the [[gonads]] (the rest being the gametes)
|AnswerB=Endoderm
|AnswerB=Endoderm
|AnswerBExp=The [[endoderm]] gives rise to:
|AnswerBExp=The [[endoderm]] gives rise to the entire alimentary canal except for the mouth, pharynx, the terminal part of the rectum (which are lined by involutions of the ectoderm), and the lining cells of all the glands which open into the digestive tube, including those of the liver, gallbladder, and pancreas. In addition, the endoderm gives rise to the respiratory tract (the trachea, bronchi, and alveoli of the lungs), endocrine system (lining of the follicles of the [[thyroid]] gland, parathyroid, and [[thymus]]), the auditory system (epithelium of the auditory tube, eustachian tube, and tympanic cavity), and the urinary system (urinary bladder and part of the [[urethra]]).
 
-  GI: the entire alimentary canal except for part of the mouth, [[pharynx]], the terminal part of the rectum (which are lined by involutions of the ectoderm), and the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas.
 
- Respiratory: the trachea, bronchi, and alveoli of the lungs
 
-  Endocrine: the lining of the follicles of the [[thyroid]] gland and [[thymus]]
 
-  Auditory system: epithelium of the auditory tube and tympanic cavity
 
-  Urinary system: urinary bladder and part of the [[urethra]]
|AnswerC=Surface ectoderm
|AnswerC=Surface ectoderm
|AnswerCExp=The surface [[ectoderm]] gives rise to:
|AnswerCExp=The surface [[ectoderm]] gives rise to the [[epidermis]] of the skin (whereas the dermis is derived from mesoderm), glands, hair, sweat glands, nails, epithelium of the mouth and nasal cavity, salivary glands, and glands of mouth and nasal cavity, mammary glands, tooth enamel (although dentin and dental pulp are derived from ectoderm), and epithelium of the [[anterior pituitary]]. The anal canal below the pectinate line also arises from the surface ectoderm. Finally, the surface ectroderm also gives rise to opthalmic structures, such as the [[lens]], [[cornea]], [[lacrimal gland]], tarsal glands, and the conjunctiva, and sensory organs of the ear and the the olfactory epithelium.
 
-  Skin (only [[epidermis]]; dermis is derived from mesoderm), glands, hair, and nails
 
-  Epithelium of the mouth and nasal cavity, salivary glands, and glands of mouth and nasal cavity
 
-  Tooth enamel (although dentin and dental pulp are derived from ectoderm)
 
-  Epithelium of the [[anterior pituitary]]
 
[[Lens]], [[cornea]], [[lacrimal gland]], tarsal glands, and the conjunctiva of the eye
 
-  Apical ectodermal ridge-inducing development of the limb buds of an embryo
 
-  Sensory receptors in epidermis
|AnswerD=Neuroectoderm
|AnswerD=Neuroectoderm
|AnswerDExp=The [[neuroectoderm]] gives rise to:
|AnswerDExp=The [[neuroectoderm]] gives rise to the [[CNS]] (brain and spinal cord), neurohypophysis, oligodendrocytes, astrocytes, ependymal cells, and pineal gland. Additionally, ophthalmic structures, such as the retina and the optic nerve, are also derived from the neuroectoderm.
 
[[Brain]] (rhombencephalon, mesencephalon, and prosencephalon)
 
-  [[Spinal cord]] and motor neurons
 
-  [[Retina]]
 
-  [[Posterior pituitary]]
|AnswerE=Neural crest
|AnswerE=Neural crest
|AnswerEExp=The [[neural crest]] gives rise to:
|AnswerEExp=The [[neural crest]] gives rise to the PNS (including celiac and dorsal root ganglia, cranial nerves, schwann cells), autonomic nervous system, pia and arachnoid mater, melanocytes, chromaffin cells of the adrenal medulla, parafollicular C cells of the thyroid gland, bones of the skull and facial cartilage, odontoblasts, ciliary body of the eye, and the aorticopulmonary septum of the developing heart.
-  Pigment cells in the [[skin]]
|EducationalObjectives=The neural crest is the embryological origin of schwann cells. Patients with NF2 may complain of vertigo, hearing loss, and tinnitus, which often suggest the presence of bilateral schwannomas, a characteristic feature of the disease.
 
|References=Evans GR. Neurofibromatosis type 2 (NF2): a clinical and molecular review. Orphanet Journal of Rare Diseases. 2009;4:16.<br>
-  Ganglia of the [[autonomic nervous system]]
First Aid 2014 page 444
 
-  Dorsal root ganglia
 
-  Facial [[cartilage]]
 
-  Spiral septum of the developing [[heart]]
 
-  Ciliary body of the eye
 
-  Adrenal medulla
|EducationalObjectives=The neural crest is the embryological origin of schwannomas.
|References=First Aid 2014 page 444
|RightAnswer=E
|RightAnswer=E
|WBRKeyword=Embryology, Neural crest, Schwannoma, Brain tumor, Cancer, Neurofibromatosis, NF2, Mesoderm, Development
|WBRKeyword=Embryology, Neural crest, Schwannoma, Brain tumor, Cancer, Neurofibromatosis, NF2, Mesoderm, Development
|Approved=Yes
|Approved=Yes
}}
}}

Latest revision as of 23:27, 27 October 2020

 
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Alison Leibowitz)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Embryology
Sub Category SubCategory::Neurology
Prompt [[Prompt::A 23-year-old man is referred to a neurologist for the evaluation of a progressively worsening vertigo and hearing loss in both ears for the past 4 months. The patient has no past medical history. The patient has no significant past medical history. He denies allergies, smoking, alcohol intake, or use of illicit drugs. A brain MRI is performed and shows bilateral cerebellopontine angle tumors. Which of the following is the most likely embryological origin of the cells from which this patient’s masses arose?]]
Answer A AnswerA::Mesoderm
Answer A Explanation [[AnswerAExp::The mesoderm gives rise to muscle, bone, connective tissue, spleen, kidneys, adrenal cortex, cardiovascular and lymphatic structures, wall of gut tube, serious linings of body cavities, vagina, ovaries, testes, and dermis.]]
Answer B AnswerB::Endoderm
Answer B Explanation [[AnswerBExp::The endoderm gives rise to the entire alimentary canal except for the mouth, pharynx, the terminal part of the rectum (which are lined by involutions of the ectoderm), and the lining cells of all the glands which open into the digestive tube, including those of the liver, gallbladder, and pancreas. In addition, the endoderm gives rise to the respiratory tract (the trachea, bronchi, and alveoli of the lungs), endocrine system (lining of the follicles of the thyroid gland, parathyroid, and thymus), the auditory system (epithelium of the auditory tube, eustachian tube, and tympanic cavity), and the urinary system (urinary bladder and part of the urethra).]]
Answer C AnswerC::Surface ectoderm
Answer C Explanation [[AnswerCExp::The surface ectoderm gives rise to the epidermis of the skin (whereas the dermis is derived from mesoderm), glands, hair, sweat glands, nails, epithelium of the mouth and nasal cavity, salivary glands, and glands of mouth and nasal cavity, mammary glands, tooth enamel (although dentin and dental pulp are derived from ectoderm), and epithelium of the anterior pituitary. The anal canal below the pectinate line also arises from the surface ectoderm. Finally, the surface ectroderm also gives rise to opthalmic structures, such as the lens, cornea, lacrimal gland, tarsal glands, and the conjunctiva, and sensory organs of the ear and the the olfactory epithelium.]]
Answer D AnswerD::Neuroectoderm
Answer D Explanation [[AnswerDExp::The neuroectoderm gives rise to the CNS (brain and spinal cord), neurohypophysis, oligodendrocytes, astrocytes, ependymal cells, and pineal gland. Additionally, ophthalmic structures, such as the retina and the optic nerve, are also derived from the neuroectoderm.]]
Answer E AnswerE::Neural crest
Answer E Explanation [[AnswerEExp::The neural crest gives rise to the PNS (including celiac and dorsal root ganglia, cranial nerves, schwann cells), autonomic nervous system, pia and arachnoid mater, melanocytes, chromaffin cells of the adrenal medulla, parafollicular C cells of the thyroid gland, bones of the skull and facial cartilage, odontoblasts, ciliary body of the eye, and the aorticopulmonary septum of the developing heart.]]
Right Answer RightAnswer::E
Explanation [[Explanation::Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disorder characterized by its predisposition to the development of tumors, namely multiple schwannomas, meningiomas, and ependymomas. In contrast to neurofibromatosis type 1 (NF1), NF2 is not classically associated with the development of neurofibromas. The hallmark of NF2 is the development of bilateral vestibular schwannomas. Patients typically present with hearing loss, tinnitus, and/or vertigo. The presence of bilateral cerebellopontine angle tumors, the age of the patient, and and the clinical involvement of the CN VIII are all characteristic of NF2. The embryological origin of schwann cells, which abnormally proliferate into bilateral schwannomas in NF2, is the neural crest. Schwann cells are highly plastic, neural crest-derived cells that ensheath the peripheral nerves. Neural crest cells migrate between the ectroderm and the neural tube during development and gives rise to the PNS (including celiac and dorsal root ganglia, cranial nerves, schwann cells), autonomic nervous system, pia and arachnoid mater, melanocytes, chromaffin cells of the adrenal medulla, parafollicular C cells of the thyroid gland, bones of the skull and facial cartilage, odontoblasts, ciliary body of the eye, and the aorticopulmonary septum of the developing heart.

Educational Objective: The neural crest is the embryological origin of schwann cells. Patients with NF2 may complain of vertigo, hearing loss, and tinnitus, which often suggest the presence of bilateral schwannomas, a characteristic feature of the disease.
References: Evans GR. Neurofibromatosis type 2 (NF2): a clinical and molecular review. Orphanet Journal of Rare Diseases. 2009;4:16.
First Aid 2014 page 444]]

Approved Approved::Yes
Keyword WBRKeyword::Embryology, WBRKeyword::Neural crest, WBRKeyword::Schwannoma, WBRKeyword::Brain tumor, WBRKeyword::Cancer, WBRKeyword::Neurofibromatosis, WBRKeyword::NF2, WBRKeyword::Mesoderm, WBRKeyword::Development
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