BRAIN MRI MEASUREMENTS

SITE

1. Frontal horn width to intercaudate distance ratio (FH/CC):

• normal FH/CC (fig.1) ratio range between 2.2 to 2.6

• as the caudate heads reduce in volume the CC distance will approach the FH distance, and the ratio will approach 1

2. Inner table to intercaudate distance ratio (CT/IC):

• normal CC/IT ratio (fig.1) range between 0.09 to 0.12

• as the caudate heads reduce in size, the CC distance will increase and as such the CC/IT ratio will increase

Fig. 1: Diagram demonstrating how to assess the frontal horn width to intercaudate distance ratio (FH/CC) and the inner table to intercaudate distance ratio (CT/IC).

References: Radiopaedia.org - courtesy of Dr. Frank Gaillard

Progressive supranuclear palsy

3. Midbrain to pons area ratio (fig.2):

• the pontomesencephalic junction is defined by a line between the superior pontine notch and the inferior border of the quadrigeminal plate

• the pontomedullary junction is defined by a line parallel to the first line, at the level of the inferior pontine notch

• normal ratio value is approximately 0.24 whereas it is significantly reduced in PSP to 0.12

Fig. 2: Diagram illustrating the midbrain to pons area ratio.

References: Radiopaedia.org - courtesy of Dr. Frank Gaillard

4. Magnetic resonance parkinsonism index (MRPI):

Is assessed by measuring (fig.3):

• the width of the superior cerebellar peduncle (SCP) in the coronal plane

• the middle cerebellar peduncle (MCP) in the sagittal plane

• the area of the midbrain (M) and pons (P) in the midsagittal plane

It is calculated by (P / M) x (MCP / SCP). Where a value of more than 13.55 indicates an abnormal result, and strongly suggests that these patients will go on to develop PSP.

Fig. 3: Diagram showing how to assess the magnetic resonance parkinsonism index (MRPI) on multiplanar T1 weighted images.

References: Radiopaedia.org - courtesy of Dr. Bruno Di Muzio

Mild cognitive impairment, Alzheimer’s disease

5. Medial temporal lobe atrophy (MTA) score (fig.4):

• it is a visual score using coronal T1 weighted images through the hippocampus at the level of the anterior pons

• it assesses three features resulting in a score from 0 to 4 (table)

• in a patient younger than 75 years of age, a score of 2 or more is abnormal and in a patient 75 years or older, a score of 3 or more is abnormal

Fig. 4: Medial temporal lobe atrophy (MTA) score.

References: Department of Radiology, Royal Melbourne Hospital - Melbourne/AU

6. The posterior atrophy score (Koedam score):

Visual assessment of parietal atrophy on MRI considering both the axial, sagittal and coronal planes and resulting in a score from 0 to 3:

• grade 0: closed sulci, no gyral atrophy

• grade 1: mild sulcal widening, mild gyral atrophy

• grade 2: substantial sulcal widening, substantial gyral atrophy (fig.5)

• grade 3: marked sulcal widening, knife-blade gyral atrophy

Fig. 5: T1 sagittal, axial and coronal weighted images in a patient with substantial parietal sulcal widening and gyral atrophy - posterior atrophy score grade 2 (Koedam score).

References: Department of Radiology, Royal Melbourne Hospital - Melbourne/AU

Vascular dementia

7. Fazekas scale for white matter lesions (fig.6):

• quantifies the amount of white matter T2 hyperintense lesions usually attributed to chronic small vessel ischaemia

• divides the white matter in periventricular and deep white matter, and each is given a grade depending on the size and confluence of lesions

Fig. 6: Axial FLAIR weighted images illustrating the Fazekas scale for white matter lesions.

References: Radiopaedia.org - courtesy of Dr. Bruno Di Muzio

8. Global cortical atrophy (GCA) scale:

• it is the mean score for cortical atrophy throughout the complete cerebrum

• cortical atrophy is best scored on FLAIR images

Cerebral amyloid angiopathy

9. Boston diagnostic criteria for cerebral amyloid angiopathy (CAA):

It tries to give uniformity on diagnosis of CAA.

It is divided in categories with neuroimaging playing a role in two of them:

• definite cerebral amyloid angiopathy and probable cerebral amyloid angiopathy with supporting pathological evidence (both depending on pathological evidence)

• probable cerebral amyloid angiopathy (with - fig.7 - or without supporting pathological evidence): MRI findings demonstrate multiple haemorrhages of varying sizes/ages with no other explanation

• possible cerebral amyloid angiopathy: MRI findings reveal a single lobar, cortical, or cortical/subcortical haemorrhage without another cause, multiple haemorrhages with a possible but not a definite cause, or some haemorrhage in an atypical location

Fig. 7: Probable cerebral amyloid angiopathy with supporting pathological evidence.

References: Department of Radiology, Royal Melbourne Hospital - Melbourne/AU

10. Middle cerebellar peduncle width (fig.8) as a measurement aiding differentiation of multiple system atrophy (MSA) from Parkinson's disease:

• pontocerebellar atrophy is the characteristic pathologic change in this MSA

• 8.0 mm or less favours MSA

Sagittal T1 weighted image showing how to assess the middle cerebellar peduncle width.References: Department of Radiology, Royal Melbourne Hospital - Melbourne/AU