Table 2. Refinement of white matter tracts into an ‘at-risk’ model of injury in NPH.

ROI	Grouping	Relevance	Discussion
SLF	Cognitive	Excluded	Whilst spatial disorientation, for example, topographical deficits, is a feature of the NPH spectrum, language disorders are not typical. This tract, with its long anterior-posterior arrangement was initially explored but found to be too prone to valve artefact.
	Spatial/ language
ILF	Cognitive	Included	Cognitive dysfunction, such as inability to match visual recognition of common objects with the functional sequences required to use them, is a feature of the NPH spectrum. This tract was included for its relevance; its long anterior-posterior arrangement adjacent to the ventricles. Its inferior position in relation to the SLF protected this tract from issues related to valve artefact.
	Visual recognition	P = lateral
IFO	Cognitive	Included	Whilst language disorders are not typical of the NPH spectrum, the long anterior-posterior arrangement of this tract and its fronto-basal position provided relevance to the frontal executive dysfunction seen in NPH. This tract was included but only specifically at the fronto-temporal point, i.e. the area of most likely distortion due to expansion of the frontal horns (combined with the UNC).
	Language	P = relatively remote
UNC	Cognitive	Included	The fronto-temporal arrangement of this tract and its participation in the limbic pathway provided relevance to the frontal executive dysfunction seen in NPH. This tract was included at the area of most likely distortion due to expansion of the frontal horns, i.e. at its point of curvature. Due to considerations of crossing fibres and the relatively reduced white matter fibre bundle sizes seen in NPH, this ROI was combined with the adjacent IFO tract at this point for purposes of enhanced consistency.
	Ventral limbic	P = relatively remote
CING	Cognitive	Excluded	The relationship of this tract to the ventricles and its participation in the limbic pathway provided relevance to the frontal executive dysfunction seen in NPH. However, the relatively large amount of surrounding CSF represented in the ROI for the cingulum bundle rendered the interpretation of this tract difficult using this methodology, and resulted in its exclusion.
	Dorsal limbic
GCC	Motor	Included	The close relationship with this tract to the ventricles and its participation in the motor pathway provided a clear relevance to the gait and balance apraxia seen in NPH. This part of the corpus callosum was included for its anterior/ frontal location.
	Contralateral executive	P = adjacent
BCC	Motor	Included	The close relationship with this tract to the ventricles and its participation in the motor pathway provided a clear relevance to the gait and balance apraxia seen in NPH. This part of the corpus callosum was included for its midpoint location between the two ventricles and its role in a potential hydrocephalic disconnection syndrome.
	Contralateral executive	P = adjacent
SCC	Motor	Excluded	The close relationship with this tract to the ventricles and its participation in the motor pathway provided a clear relevance to the gait and balance apraxia seen in NPH. However, the GCC and BCC were deemed to be the stronger and more relevant ROIs.
	Contralateral executive
ALIC	Cognitive	Excluded	Behavioural syndromes are possible in, but not typical of, NPH. The PLIC tract was also deemed to be far superior as a ROI in both functional and neuroanatomical considerations.
	Behaviour
ATR	Cognitive	Included	This thalamocortical fibre pathway is found in the medial portion of the ALIC. However, its prefrontal cortical projections provide more relevance than ALIC to the likely areas of distortion due to the expansion of the frontal horns. This tract has been implicated both in poor cognitive performance in vascular dementia and psychopathology, such as schizophrenia, and was therefore included.
	Behaviour	P = lateral
GIC	Sensory	Excluded	Sensory syndromes are not typical of NPH. The PLIC tract was deemed far superior as a ROI.
PLIC	Motor	Included	The key role of the corticospinal tract in gait and balance dysfunction provided a clear relevance to NPH. In addition, the superior-inferior arrangement of this tract, relatively remote to the ventricles, provided a good comparator to other relevant tracts that were adjacent and lateral to the ventricles.
		P = relatively remote

SLF = superior longitudinal fasciculus, ILF, inferior longitudinal fasciculus, IFO = inferior fronto-occipital fasciculus, UNC = uncinate fasciculus, CING = cingulum, GCC = genu of the corpus callosum, BCC = body of the corpus callosum, SCC = splenium of the corpus callosum, ALIC = anterior limb of the internal capsule, GIC = genu of the internal capsule, PLIC = posterior limb of the internal capsule, P = position in relation to lateral ventricles