Answer for BIR CoW 22 Dec 2024
NORMAL PRESSURE HYDROCEPHALUS / SHUNT RESPONSIVE HYDROCEPHALUS
Findings
Prominent VR spaces in bilateral thalami and basal ganglia regions - Etat Crible Evan's Index 0.32 Anteroposterior Lateral Ventricular Index 0.53 Callosal angle 87 deg Upward bowing of Corpus Callosum Multiple lacunar infarcts in pons and bilateral thalami Chronic infarct in bilateral gangliocapsular region Multifocal gradient blooming in cerebellar hemispheres and thalamic region - microhemorrhages Small Vessel Ischemic Changes Grade II Partial empty sella PC CSF Flow Study: Peak Systolic Velocity 7.6 cm/s; Stroke Volume - 49 microlitres. Stroke Volume increased to shunt responsive range.
Discussion
To be diagnosed with NPH, patients must first have enlarged ventricles and at least a portion of the clinical triad. The gait disturbance is usually the first symptom to appear, followed by dementia and finally urinary incontinence. The best response to shunting occurs earlier in disease when gait is the primary symptom. Some patients who had only dementia were shunted, with obviously poor results, which led some to question the very existence of NPH. Today, up to 10% of patients with dementia may have NPH and therefore may be treatable by shunting. Of course, such patients will also have a gait disturbance. When an elderly patient presents with a gait disturbance suggestive of NPH, the first diagnostic test is usually MR imaging looking for ventricular dilation out of proportion to any sulcal enlargement (i.e., the of communicating hydrocephalus rather than atrophy). The amount of interstitial edema surrounding the lateral ventricles should be minimal to absent (which corresponds with the normal mean intraventricular pressure). There is frequently associated evidence of deep white matter ischemia, also known as small-vessel ischemia or leukoaraiosis. The third ventricle walls, which generally bow inward producing a waist, become parallel or even bowed out and may have a prominent CSF flow void extends down through aqueduct to the obex of the fourth ventricle. The CSF flow void is indicative of hyperdynamic CSF flow similar to the flow voids seen in arteries on MR imaging. The extent of the CSF flow void on conventional spin-echo images in the past was found to correlate with a response to ventriculoperitoneal shunting. Unfortunately, the more modern MR imaging techniques such as fast/turbo spin-echo. Patients who respond to shunting NPH have at least twice the ACSV of healthy elderly patients. This is because they have enlarged ventricles and minimal, if any, atrophy. As noted above, when the brain expands during systole in healthy elderly patients, it expands outward toward the SAS and inward toward the ventricles. In patients with NPH, the brain is already expanded out against the inner table of the calvarium, so all systolic expansion is directed inward against the enlarged ventricles. This drumhead of the enlarged ventricles leads to hyperdynamic CSF flow the aqueduct, which we measure as an elevated CSV. If these patients are not shunted, they will eventually develop atrophy and the amount of systolic expansion and the ACSV will be reduced. Thus, hyperdynamic CSF flow indicates atrophy has not yet taken place. With a fixed voltage drop that now conduct twice much current, a potential parallel pathway for CSF resorption would be the extracellular space of the brain. Thus, CSF would cross the ependyma into the ISP and be transported out the venous Virchow-Robin spaces via the aquaporin-4 water channels. These patients would continue with this dual pattern of CSF resorption, with some of the CSF gliding over the myelin lipid until their elderly years when they develop DWMI, which might be considered the second “hit” in this disease. The histopathologic hallmark of DWMI is myelin pallor. With less lipid, there is more water and a high signal on T2-weighted and FLAIR images. The outward-flowing CSF in the ISP of the brain is no longer gliding over the myelin lipid but is now attracted to the myelin protein. This attraction between the polar water molecules of the CSF and the charged side groups of the myelin protein increases the resistance to CSF outflow via the extracellular or inter space of the brain. The outflowing CSF is essentially dammed by the DWMI, and this process leads to hydrocephalus. According to Hakim’s hypothesis, the tangential shearing forces near the ventricles lead to gait disturbance, and the subsequent radial shearing forces compress the cortex against the inner table of the calvarium, leading to dementia. In support of the above hypothesis is the finding that there is more water in the extracellular space of the brain in patients with NPH than in image-matched controls. This finding is because the apparent diffusion coefficient from diffusion-weighted imaging is elevated compared with that in healthy individuals.
Reference:
CSF Flow in the Brain in the Context of Normal Pressure Hydrocephalus, W.G. Bradley, Jr AJNR Am J Neuroradiology 2015, 36 (5) 831-838
Findings
Prominent VR spaces in bilateral thalami and basal ganglia regions - Etat Crible Evan's Index 0.32 Anteroposterior Lateral Ventricular Index 0.53 Callosal angle 87 deg Upward bowing of Corpus Callosum Multiple lacunar infarcts in pons and bilateral thalami Chronic infarct in bilateral gangliocapsular region Multifocal gradient blooming in cerebellar hemispheres and thalamic region - microhemorrhages Small Vessel Ischemic Changes Grade II Partial empty sella PC CSF Flow Study: Peak Systolic Velocity 7.6 cm/s; Stroke Volume - 49 microlitres. Stroke Volume increased to shunt responsive range.
Discussion
To be diagnosed with NPH, patients must first have enlarged ventricles and at least a portion of the clinical triad. The gait disturbance is usually the first symptom to appear, followed by dementia and finally urinary incontinence. The best response to shunting occurs earlier in disease when gait is the primary symptom. Some patients who had only dementia were shunted, with obviously poor results, which led some to question the very existence of NPH. Today, up to 10% of patients with dementia may have NPH and therefore may be treatable by shunting. Of course, such patients will also have a gait disturbance. When an elderly patient presents with a gait disturbance suggestive of NPH, the first diagnostic test is usually MR imaging looking for ventricular dilation out of proportion to any sulcal enlargement (i.e., the of communicating hydrocephalus rather than atrophy). The amount of interstitial edema surrounding the lateral ventricles should be minimal to absent (which corresponds with the normal mean intraventricular pressure). There is frequently associated evidence of deep white matter ischemia, also known as small-vessel ischemia or leukoaraiosis. The third ventricle walls, which generally bow inward producing a waist, become parallel or even bowed out and may have a prominent CSF flow void extends down through aqueduct to the obex of the fourth ventricle. The CSF flow void is indicative of hyperdynamic CSF flow similar to the flow voids seen in arteries on MR imaging. The extent of the CSF flow void on conventional spin-echo images in the past was found to correlate with a response to ventriculoperitoneal shunting. Unfortunately, the more modern MR imaging techniques such as fast/turbo spin-echo. Patients who respond to shunting NPH have at least twice the ACSV of healthy elderly patients. This is because they have enlarged ventricles and minimal, if any, atrophy. As noted above, when the brain expands during systole in healthy elderly patients, it expands outward toward the SAS and inward toward the ventricles. In patients with NPH, the brain is already expanded out against the inner table of the calvarium, so all systolic expansion is directed inward against the enlarged ventricles. This drumhead of the enlarged ventricles leads to hyperdynamic CSF flow the aqueduct, which we measure as an elevated CSV. If these patients are not shunted, they will eventually develop atrophy and the amount of systolic expansion and the ACSV will be reduced. Thus, hyperdynamic CSF flow indicates atrophy has not yet taken place. With a fixed voltage drop that now conduct twice much current, a potential parallel pathway for CSF resorption would be the extracellular space of the brain. Thus, CSF would cross the ependyma into the ISP and be transported out the venous Virchow-Robin spaces via the aquaporin-4 water channels. These patients would continue with this dual pattern of CSF resorption, with some of the CSF gliding over the myelin lipid until their elderly years when they develop DWMI, which might be considered the second “hit” in this disease. The histopathologic hallmark of DWMI is myelin pallor. With less lipid, there is more water and a high signal on T2-weighted and FLAIR images. The outward-flowing CSF in the ISP of the brain is no longer gliding over the myelin lipid but is now attracted to the myelin protein. This attraction between the polar water molecules of the CSF and the charged side groups of the myelin protein increases the resistance to CSF outflow via the extracellular or inter space of the brain. The outflowing CSF is essentially dammed by the DWMI, and this process leads to hydrocephalus. According to Hakim’s hypothesis, the tangential shearing forces near the ventricles lead to gait disturbance, and the subsequent radial shearing forces compress the cortex against the inner table of the calvarium, leading to dementia. In support of the above hypothesis is the finding that there is more water in the extracellular space of the brain in patients with NPH than in image-matched controls. This finding is because the apparent diffusion coefficient from diffusion-weighted imaging is elevated compared with that in healthy individuals.
Reference:
CSF Flow in the Brain in the Context of Normal Pressure Hydrocephalus, W.G. Bradley, Jr AJNR Am J Neuroradiology 2015, 36 (5) 831-838
Note:
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!