Spinal cord stimulator 

Make sure you know the history of all previous spine surgeries-- especially previous lamis. Look at the imaging. 

MAC anesthesia

Prone with back as flat as possible where you plan to enter. 

- C-arm in AP view, go live and move it around until you see the interlaminar spaces clearly 

- Go in two levels below where you plan to enter -- Put the coude needle on the skin and use xray to localize.  

i.e. if you want to enter T12-L1 interlaminar space, put needle in near pedicle of L2 (red), dock on lamina of L1 (blue), and enter the T12-L1 interlaminar spac (green) 

- needle goes in bevel UP

Ways to determine you are in the epidural space

- using your hands to get the haptic feedback of popping through ligamentum flavum, stop after you feel that. Downside: requires skill and experience. 

- syringe full of air that you periodically push against until you reach loss of resistance. Downside: air does not conduct, if you inject too much into the epidural space you won't be able to trial the electrodes during the case. 

- syringe full of water that you periodically push against until water starts to enter. Downside: if clear fluid comes out of needle, you won't know if its water that you injected epidurally or CSF

- Aim for direct midline placement

- Plug the electrode into the white box then extension leads. Wake up the patient intraop. The reps trial different settings and figure out if the pain area is covered. 

- Pull the coude needle out, tape the leads onto the skin and 

Pediatric neuroblastoma

- 3rd most common pediatric tumor after leukemia and primary brain

- originates from "neuroblasts" - essentially precursor neural crest cells, which make multipotential progenitor cells that give rise to the peripheral nervous system including dorsal root ganglia, the enteric nervous system, sympathetic chain, pigment cells, Schwann cells, adrenal medullary cells, cells of the craniofacial skeleton (including odontoblasts) -- within the brain, neural crest cells form nerve sheaths of cranial nerves 5/7/9/10, the optic vesicle (i.e. may eye structures like iris/cornea, as well as skeletal muscle that attach the eye to the skull), otic capsule/inner ear
- you can derive a neuroblastoma anywhere you have any of the above cells; most common is adrenal medulla in the abdomen, and along paraspinal sympathetic ganglia.
- depending on the degree of differentiation of the tumor stem cell, the resultant tumor will be  neuroblastoma, ganglioneuroblastoma, or ganglioneuroma in order of least to most differentiated. as you would expect, prognosis is better the more differentiated the origin cell line.
- paragangliomas i.e are tumors derived from chromaffin cells, which are differentiated neural crest

- 50-70% are metastatic by the time they are found - liver, lymph nodes, bone. This is because neural crest cells are undergo an epithelial to mesenchymal transition early on in their development,  and thus acquire enhanced migratory abilities and decreased requirements for intercellular contact. this allows the cells to leave the neural tube and go about the body.

- CNS mets are not very common, but when they happen, its nearly always to bone - calvaria and skull base. Especially at junction of lateral orbital wall and greater wing of sphenoid. They can also metastasize to dura and will typically expand along exterior aspect of dura between dura and bone. They have a characteristic "sunburst" appearance --- ddx also includes ewing's

- as treatment for neuroblastoma improves, the rate of CNS involvement is increasing - this is likely because kids are living longer with the disease, and the chemo that they get that achieves tumor control may not have good BBB penetration, which means the CNS may be a sanctuary site for the tumor. 

- very rarely will metastasize to brain parenchyma, into ventricles, or leptomeningeally - parenchymal mets often will bleed or be calcified, qualities which are rare among pediatric brain tumors 

- Imaging - they show a sunburst/hairlike projections of bone into tumor -- this is from rapid, aggressive growth of tumor causing a periosteal reaction. Other tumors that do the hair thing - ewing's sarcoma (used to be believed that they had a neuroblast origin cell - actually its a fusion gene expressed in mesenchymal stem cells), other sarcoma, lymphoma/solid leukemia

Helpful papers: 

https://www.ncbi.nlm.nih.gov/pubmed/19353343 - Calvarial lesions: a radiological approach to diagnosis.

https://www.ncbi.nlm.nih.gov/pubmed/20410407 - Imaging of metastatic CNS neuroblastoma.

Visual system

Optic Tract 

LGN

- The vast majority (~80%) of retinal ganglion neurons terminate in the LGN, which is a dorsal thalamic structure.
- BUT 80% of the excitatory input to the LGN comes not from retina but V1 and other cortical structures -- truly, it is the case that the eyes do not see what the mind does not know
- LGN also receives input from brainstem nuclei involved in attentiveness, which may be another way that attention modifies not only how well we see but what we see



Histologically, the LGN is a 6-layered structure

- Neurons from ipsilateral eye terminate on layers, 2, 3, and 5

- Neurons from contralateral eye terminate on layers, 1, 4, 6

- Layers 1 and 2 contain larger nuclei than those of layers 3-6 and are called magnocellular and parvocellular, and they contain input form the magnocellular (bigger receptive field, fast processing, low-contrast stimuli -- important for motion) and parvocellular (smaller receptive field, important for color, detail, and shape) retinal ganglion neurons, respectively. 

- the non-staining layers in between are koniocellular (greek for dust) - unknown function 

 LGN on MRI

now why does this GBM patient have homonymous hemianopsia? it looks like the T2 signal is invading into the distal optic tract, possibly LGN, and all of the bundles of right optic radiation. Remember: when its GBM, the T2 is not edema, its tumor.

Other places where retinal nuclei project:

- superior colliculus - important for coordinating eye movements - fixation (staring at one point, adjustments only to compensate for head motion), smooth pursuit (following one object smoothly over time), saccades (rapid movement in one direction) and vergence (eyes moving independently to maintain binocular/focused motion). Outputs go, as one would expect, to the nuclei of CN 3, 4, and 6. In higher primates, most of input to superior colliculus is not retina but visual cortex and frontal eye fields. 

- suprachiasmatic nucleus in hypothalamus - important for circadian rhythms and day/night cycles 

- pretectum - pupillary light reflex 

LGN to Visual cortex 

- There are two or three tracts depending on who you asked, and they can be named upper/lower, anterior/middle/posterior, ventral/dorsal etc. But the point is there is a bundle of fibers that carry upper visual quadrant information (meyer's loop) through temporal lobe and that terminates in the lower bank of the calcarine sulcus (lingual gyrus) and a bundle of fibers that carry lower visual quadrant information through the parietal lobe that terminates in the upper bank of the calcarine sulcus (the cuneus)
- The anatomy of meyer's loop is highly variable -- in some people, it will project all the way to the temporal pole. The traditional teaching that anterior/inferior temporal lobe is safe to resect is not always 100% true.

V1 lines the calcarine sulcus and extends into occipital pole

From V1, there is the dorsal stream "where" stream into parietal lobe (identifying motion, and relative positions in space of objets) and the ventral stream "what" stream into temporal lobe (object and person recognition). More on that next time 

sources

http://journal.frontiersin.org/article/10.3389/fnana.2010.00015/full

http://thebrain.mcgill.ca/flash/i/i_02/i_02_cr/i_02_cr_vis/i_02_cr_vis.html

http://iovs.arvojournals.org/article.aspx?articleid=2480802

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3236807/pdf/nihms319970.pdf

Septal nuclei, third ventricular lateral wall anatomy

Speech

Brodmann area 44 (pars opercularis) and 45 (pars triangularis)

Other important brodmann's areas:
- 6 - premotor/sma
- 3, 1, 2 - S1
- 8 - frontal eye fields
- 17, 18 - V1
- 41, 42 - A1
- totally irrelevant in clinical practice but somehow you will continue to get pimped on and tested on them

From Chang et al 2017 in JNS:

MNI map of incidence of effects of stimulation

compiled map of probability of speech arrest -- note how it goes up to MFG and STG and even into T2/MTG. 

Wernicke's area is classically defined as the posterior STG as such:

anomia with stim

Blue = A1: aka heschl's gyrus 

Heschl's gyrus - A1

The fusiform aka (lateral and medial) occipitotemporal gyrus: 

Fusiform gyrus (red), ITG (green), parahippocampal (blue), lingual (yellow), inf occipital (yellow), collateral sulcus (green line), collateral sulcus (green line), mid-fusiform sulcus (purple)


- between paraphippcampal gyrus, ITG, and lingual.
- important for facial recognition (involved in prosopagnosia, facial halluncinations like charles-bonnet), written-word recognition (dyslexia), color processing along with angular gyrus (synesthesia)
- part of ventral stream, necessary for differentiating categories of objects


image source, image source