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Hippocampal Subfield Group

Apr 14, 2021 • 10 tweets • 6 min read • Read on X

Happy #SubfieldWednesday! Today we will be sharing a 🧵 on anatomical variability in the medial temporal lobe (MTL). MTL subregions vary in size and shape across individuals & these variations can make landmark identification and segmentation difficult

#SubfieldWednesday (1/n)

Today we will focus on the *most* consistent structure in the MTL: the hippocampal body. Most of our followers will be familiar with this canonical hippocampal body shape shown below in the coronal plane.

#SubfieldWednesday (2/n)

The shape is characterized by a consistent “C-shape” when viewed in the coronal plane. The C is formed by the cornu ammonus (CA) subfield on the lateral part of the hippocampal body.

#SubfieldWednesday (3/n)

But do all individuals have hippocampal body slices that look like this?

#SubfieldWednesday (4/n)

A variation that is observed in healthy individuals is a more "narrow" or round-shape of the hippocampal body in the coronal plane. This variant is referred to as “malrotation” or “incomplete hippocampal inversion.”

frontiersin.org/articles/10.33…

#SubfieldWednesday (5/n)

Malrotation occurs more often in the left hemisphere than in the right, and it is usually accompanied by a very deep and vertically-oriented collateral sulcus (see below for examples).

#SubfieldWednesday (6/n)

@RosenbaumLab

@RosenbaumLab, @rosanna_olsen, Fuqiang Gao and colleagues reported a case of hippocampal amnesia with malrotation in both hemispheres in 2014: dx.doi.org/10.1016/j.neur…

#SubfieldWednesday (7/n)

In summary, the length of the hippocampal body in the vertical (sup/inf) and horizontal (med/lat) dimensions can vary across subjects (and across slices within a subject). Thus, subfield boundary definitions need to take these variations into account.

#SubfieldWednesday (8/n)

The Hippocampal Subfield Group has considered these variations when developing our harmonized protocol, so that the subfield boundaries are both valid and reliable across these anatomical variations.

#SubfieldWednesday (9/n)

Next week we will talk about anatomical variability in the hippocampal head—which is more prevalent than variations in the hippocampal body. See Ding & Van Hoesen, The Journal of Comparative Neurology, 2015 for a sneak preview!

#SubfieldWednesday (end)

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More from @hipposubfields

Hippocampal Subfield Group

@hipposubfields

Jun 16, 2021

@DrAnaDaugherty

Guest post by @DrAnaDaugherty on hippocampal (Hc) vascularization.

Brought to you by “anastomosis” (noun): a cross-connection between adjacent blood vessels; plural “anastomoses”.

As in, “Wow! 54 years of mapping anastomoses”

#SubfieldWednesday 🧵 1/

The unique features of its arteries make Hc vulnerable to anoxia. Superficial arteries travel long tangential routes, and intrahippocampal arteries have few anastomoses and travel with the rolling CA and dentate gyrus tissue. 2/

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Posterior cerebral (PCA) & anterior choroidal (AChA) arteries supply Hc. Variations are noted: PCA supply is typical and dominant, AChA supply is not seen in 30-40% of hemispheres.

🚨Anastomosis Alert (arrows) 3/

tinyurl.com/2hjaw6vj

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Read 10 tweets

Hippocampal Subfield Group

@hipposubfields

May 12, 2021

Last week we talked about hippocampal variability in the hippocampal head.

The hippocampal tail is another area of the hippocampus that can vary anatomically across individuals

#SubfieldWednesday (1/n)

But first, what do we mean by the hippocampal tail? Definitions vary, but one way to define the tail is the part of the hippocampus located posterior to the corpora quadrigemina (i.e. superior and inferior colliculi).

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@thomcat992

The hippocampal dentations that can be visualized in the hippocampal body on the sagittal plane (pointed out earlier by @thomcat992). But they can also often be seen in the coronal plane in the hippocampal tail (as shown by @lemwisse and colleagues).

#SubfieldWednesday (3/n)

Read 9 tweets

Hippocampal Subfield Group

@hipposubfields

May 5, 2021

Today we continue our thread series discussing anatomical variability in the medial temporal lobe (MTL). Today’s topic is anatomical variability in the hippocampal head with a focus on the hippocampal digitations. 🍤🤓📢

#SubfieldWednesday (1/n)

But first, what do we mean by the hippocampal head? We are talking about the anterior part of the hippocampus that contains or is adjacent to the uncus.

#SubfieldWednesday (2/n)

Now what about those “hippocampal digitations” ?

Ding & Van Hoesen (2015) describe external and internal digitations. The external digitations are the “bumps” that extend dorsally and the interior digitations are the “bumps” that extend ventrally.

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Read 7 tweets

Hippocampal Subfield Group

@hipposubfields

Feb 10, 2021

@MarkCembrowski

We are pleased to announce that today we have a guest #SubfieldWednesdsay 🧵 from @MarkCembrowski !

Check it out below!

(1/n)

When you look at a textbook diagram hippocampus, one sees a series of subfields - DG, CA3, and CA1. All of these regions have specialized properties relative to one another. But it raises the question: within each region, are the cell types uniform?

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CA1 pyramidal cells of the rodent brain, one of the most studied neuron types in the brain, provide a good starting point to answer this question from both structural and functional perspectives.

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Hippocampal Subfield Group

@hipposubfields

Dec 17, 2020

Is anyone planning to do some reading about hippocampal neuroanatomy over the holidays?

If you answered, "yes", this week's #SubfieldWednesday is for you! We will give you a list of "must read" atlas references about our favorite brain structure. 🍤❣️

#SubfieldWednesday (1/n)

In our 2015 paper (Yushkevich et al., NeuroImage, 2015), we provided a list of common atlases used for hippocampal subfield definition across labs.

#SubfieldWednesday (2/n)

One of the most commonly used atlases cited was:

Duvernoy, H. M. (2005). The human hippocampus: functional anatomy, vascularization and serial sections with MRI. Springer Science & Business Media.

#SubfieldWednesday (3/n)

Read 10 tweets