Challenges in Identifying the Foot Motor Region in Patients with Brain Tumor on Routine MRI: Advantages of fMRI

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Figure.
Axial T1-weighted without (A) or with (B) coregistered functional MR images obtained during a bilateral finger-tapping and foot motor paradigm. The raters were asked to identify the foot motor homunculus solely on the basis of the anatomic images (A) without the benefit of fMRI (B). fMRI places the extra-axial lesion just posterior to the primary motor gyrus, including the foot motor portion of the motor homunculus. Edema extends to involve both the precentral and postcentral gyri. The average arrow placement from the foot motor center was 16 mm in those with fMRI experience and 23 mm in those without it. A higher percentage of raters with fMRI experience than those without it placed the arrow in the motor gyrus (65% versus 50%). Eighteen percent of raters with fMRI experience correctly identified the tumor as not being located in the foot motor cortex, while 33% of raters without fMRI experience did so. Last, 35% and 39% of raters with and without fMRI experience, respectively, correctly identified the tumor as not being located in the motor gyrus. Most of the incorrect arrow placements were due to the arrow being placed in a gyrus posterior to the motor gyrus.

Table 1:

Summary of patient characteristics

Patient	Sex	Age (yr)	Tumor Location	Pathology	Previous Surgery
1	M	64	L	Grade IV GBM	No
2	F	56	R	Grade IV GBM	No
3	M	36	R	Low-grade astrocytoma	No
4	M	38	L	High-grade glioma	No
5	M	66	R	Grade II meningioma	Yes
6	F	48	L	Glioma with astrocytic and oligodendroglial features	No
7	F	26	R	Glioma with astrocytic and oligodendroglial features	No
8	F	59	L	Metastatic adenocarcinoma	No
9	F	64	R	Grade IV GBM	Yes
10	F	65	R	Metastatic breast carcinoma	Yes
11	F	58	R	Metastatic adenocarcinoma	No
12	M	58	L	Grade IV GBM	Yes
13	F	51	R	Meningioma	No
14	F	53	L	Grade IV GBM	No

Table 2:

Rater comparisons: no versus any fMRI experience^{^a}

	No fMRI Experience	Any fMRI Experience	P Value
Distance from foot motor centroid	20 ± 13 mm	13 ± 6 mm	2 × 10^{−6^b}
Arrow in motor gyrus	47% (118/252)	67% (160/238)	7 × 10^{−5^b}
Tumor in foot motor cortex	73% (183/252)	81% (192/238)	.121
Tumor in motor gyrus	66% (167/252)	76% (181/238)	.06

↵a Numbers in parentheses indicate the number of correct responses over the total number of responses (eg, in the no fMRI group, there were 18 raters for each of the 14 cases, making 252 total responses).
↵b Significant (P ≤ .05).

Table 3:

Rater comparisons by fMRI experience^{^a}

	0 Per Month	≤1 Per Month	2–5 Per Month	Significant Comparisons
Distance from foot motor centroid	20 ± 13 mm	13 ± 6 mm	12 ± 7 mm	0 vs <1, 0 vs 2–5
Arrow in motor gyrus	47% (118/252)	68% (133/196)	64% (27/42)	0 vs <1
Tumor in foot motor cortex	73% (183/252)	80% (156/196)	86% (36/42)
Tumor in motor gyrus	66% (167/252)	74% (146/196)	83% (35/42)

↵a Numbers in the parentheses indicate the number of correct responses over the total number of responses (eg, in the no fMRI group, there were 18 raters for each of the 14 cases, making 252 total responses).

Table 4:

Rater comparisons by specialty^{^a}

	Neuroradiologist	Nonradiologist	P Value
Distance from foot motor centroid	15 ± 8 mm	20 ± 14 mm	.005^{^b}
Arrow in motor gyrus	61% (206/336)	46% (71/154)	.008^{^b}
Tumor in foot motor cortex	78% (261/336)	74% (114/154)	.515
Tumor in motor gyrus	72% (242/336)	69% (106/154)	.569

↵a Numbers in the parentheses indicate the number of correct responses over the total number of responses (eg, in the neuroradiologist group, there were 24 raters for each of the 14 cases, making 336 total responses).
↵b Significant (P ≤ .05).