Neuroanatomy TOTD #8🧵
1/8 MRI shows the hippocampal formation; the hippocampus(HC) is a ridge of archicortex gray matter at floor of lat ventricle, in the med temp lobe #FOAMed #FOAMrad #radres #neurorad #neuroscience #medtwitter #radiology #neurology #neurosurgery #neuroanatomy Image
2/8..The HC: complex structure of limbic system; encodes memories from short->long term (also involved in pattern recognition,memory encoding & association, working memory,spatial nav, emotional behavior,awareness of conscious knowledge). Am I missing anything neuroscientists?
3/8...Anatomically: the HC is made of the cornu ammonis (CA) and dentate gyrus (DG); hippocampal formation also includes the subiculum and entorhinal cortex (EC). Can also be divided into head/body/tail. Supplied primarily by the PCA, and variably by anterior choroidal artery. Image
4/8...The entorhinal cortex acts as the hub connecting multiple areas of cortex to the hippocampus (both inputs and outputs); it’s histologically distinct (6 layers), and located along the anteromedial margin of the parahippocampal gyrus. Image
5/8...EC inputs go both to the dentate gyrus and CA1 cells of the CA. EC gets output from the subiculum (which is the main output hub of the hippocampus). The CA and DG curve into each other, and are separated by the hippocampal sulcus. Image
6/8...The CA is divided into CA1,CA2,CA3,CA4 cells. Circuits through HC are involved in encoding semantic (polysynaptic) & episodic & spatial (direct intra-hippocampal) memory. The HC is thought to alter the strength of networks via long term potentiation—a separate discussion!) ImageImageImage
7/8..Note the hippocampus is somewhat fragile and easily damaged by toxic, oxidative, or glucocorticoid stress. This is a case of medial temporal sclerosis, commonly assoc/w intractable temporal lobe seizures. MRI shows HC atrophy, increased T2 signal, and loss of architecture. Image
8/8...Another relatively common pathology affecting the MTL/hippocampus--HSV encephalitis--caused by reactivation of latent HSV within the trigeminal ganglion. HSV has a particular affinity for the limbic system. T2 signal abnormality and cortical expansion of the temporal lobe. Image
9/8

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More from @aaronrutman

30 Oct
Neuroanatomy TOTD #10🧵 
1/5 Small gray matter structure at the junction of the thalamus and midbrain is the subthalamic nucleus (STN).

#meded #FOAMed #FOAMrad #medtwitter #medstudents #radiology #neurorad #radres #neurology #neurosurgery #neuroanatomy #neuroanatomyTOTD Image
2/5...The STN is functionally a node within the basal ganglia (BG) INDIRECT LOOP. STN contains excitatory glutaminergic neuronsâžžoutput to the GABA neurons of GPi, which in turn have inhibitory effect on thalamic outputs to the motor cortex. Image
3/5...Loss of nigrostriatal input in Parkinsons Dzâžžincreased inhibitory output from GPiâžždecreased thalamic stimulation of the motor cortex (through both direct and indirect loop circuits). Makes sense that DBS treatments were initially directed at disrupting activity in GPi. Image
Read 5 tweets
23 Oct
Neuroanatomy TOTD #9🧵
1/6 The trigeminal n. courses anteriorly➡️prepontine cistern➡️into Meckel’s cave (green), which lies at the medial floor of middle cranial fossa at the petrous apex.
#meded #FOAMed #FOAMrad #neurorad #neurology #neurosurgery #neuroanatomy #neuroanatomyTOTD Image
2/6...Meckel’s cave (MC) is open to the subarachnoid space at its posterior margin (and is therefore filled with CSF). The trigeminal (Gasserion) ganglion lives in MC. Superiomedial to MC (and sharing a dural border), is the cavernous sinus. #radres #neurorad Image
3/6...Coursing anteriorly, the V1 and V2 branches of CNV exit MC to travel within the lateral wall of the cavernous sinus. V3 courses inferiorly to exit the middle cranial fossa through foramen ovale, without involving the cavernous sinus. Image
Read 6 tweets
6 Oct
Neuroanatomy TOTD #7🧵

1/7 The cavernous sinuses (CS) are outlined on either side of the sella. The ICA & cranial nerves 3,4,6,V1,V2 travel through the CS.

#meded #FOAMed #FOAMrad #radres #neurorad #medtwitter #radiology #neurology #neurosurgery #neuroanatomy #neuroanatomyTOTD Image
2/7...CN 3,6,V1 travel between two dural layers in the lateral wall of the CS. V2 often travels in the the inferolateral wall of the CS (sometimes inferior to the CS). Cranial nerve 6 floats freely in the CS (why CS pathology often selectively affects CN6). Image
3/7...Note that: postganglionic sympathetic inputs to the orbit (originating from the sup cervical ganglion) ascend with the ICA, branch off the ICA in the CS, and then join branches of CN3 (to sup tarsal muscle) and V1 (pupillary dilation).
Read 8 tweets
29 Sep
Neuroanatomy TOTD #6
a) Ant choroidal artery infarct, involving the post limb of the internal capsule
b) Sup hypophyseal artery aneurysm—medially directed from the supraclinoid ICA
#meded #FOAMed #FOAMrad #radres #neurorad #radiology #neurosurgery #neuroanatomy #neuroanatomyTOTD ImageImage
ICA segments: C1 (cervical) becomes C2 (petrous) in the carotid canal of the petrous bone. Becomes C3 (lacerum) as it exits the carotid canal above the foramen lacerum. Becomes C4 (cavernous segment above the petrolingual ligament through the cavernous sinus. Image
...C5 (clinoid) above proximal to the distal dural ring. C6 (ophthalmic) is truly intracranial. C7 (communicating) distal to the Pcomm. Alternative segmentation schemes include C1-C4 (cervical, petrous, cavernous, supraclinoid/terminal) Image
Read 5 tweets
24 Sep
Neuroanatomy TOTD #5

The indicated bundle is the anterior commissure (AC), located at the ant border of the 3rd ventricle, at the sup margin of the lamina terminalis.

#meded #FOAMed #FOAMrad #radres #neurorad #medtwitter #radiology #neurosurgery #neuroanatomy #neuroanatomyTOTD Image
The AC runs across the midline in front of the anterior columns of the fornix, behind the basal forebrain and beneath the anterior limb internal capsule and basal ganglia, surrounded by the bed nucleus of the stria terminalis.
The AC connects areas of the bilateral temporal poles and orbitofrontal cortex. Function is not entirely understood but it is thought to be important in the olfactory pathway and pain sensation, among other things.
Read 6 tweets
21 Sep
Neuroanatomy TOTD #4
1/5 Answer: The orange structure is the cavernous sinus (CS), a paired dura-lined venous cavity on either side of the sella. The sinuses are split into numerous “caves” by fibrous septae (hence the name). #neuroanatomy #neurorad #medtwitter #neuroanatomyTOTD Image
2/5 Note that the paired sinuses are often variably connected by “intercavernous sinuses”. While the CS is often taught for its relationship to the ICA and cranial nerves, I find that medical students and residents rarely understand the flow of blood through the sinus.
3/5 The CS receives blood from sup. and inf. ophthalmic veins draining the orbit--This is how a facial/orbital infection spreads intracranially to CS (classic #usmle ?). The sphenoparietal sinus as well as the superficial middle and inferieor cerebral veins also feed into the CS. Image
Read 5 tweets

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