The role of dynamic susceptibility contrast-enhanced perfusion MR imaging in differentiating between infectious and neoplastic focal brain lesions: results from a cohort of 100 consecutive patients

Abstract

Background and purpose: Differentiating between infectious and neoplastic focal brain lesions that are detected by conventional structural magnetic resonance imaging (MRI) may be a challenge in routine practice. Brain perfusion-weighted MRI (PWI) may be employed as a complementary non-invasive tool, providing relevant data on hemodynamic parameters, such as the degree of angiogenesis of lesions. We aimed to employ dynamic susceptibility contrast-enhanced perfusion MR imaging (DSC-MRI) to differentiate between infectious and neoplastic brain lesions by investigating brain microcirculation changes.

Materials and methods: DSC-MRI perfusion studies of one hundred consecutive patients with non-cortical neoplastic (n = 54) and infectious (n = 46) lesions were retrospectively assessed. MRI examinations were performed using a 1.5-T scanner. A preload of paramagnetic contrast agent (gadolinium) was administered 30 seconds before acquisition of dynamic images, followed by a standard dose 10 seconds after starting imaging acquisitions. The relative cerebral blood volume (rCBV) values were determined by calculating the regional cerebral blood volume in the solid areas of lesions, normalized to that of the contralateral normal-appearing white matter. Discriminant analyses were performed to determine the cutoff point of rCBV values that would allow the differentiation of neoplastic from infectious lesions and to assess the corresponding diagnostic performance of rCBV when using this cutoff value.

Results: Neoplastic lesions had higher rCBV values (4.28±2.11) than infectious lesions (0.63±0.49) (p<0.001). When using an rCBV value <1.3 as the parameter to define infectious lesions, the sensitivity of the method was 97.8% and the specificity was 92.6%, with a positive predictive value of 91.8%, a negative predictive value of 98.0%, and an accuracy of 95.0%.

Conclusion: PWI is a useful complementary tool in distinguishing between infectious and neoplastic brain lesions; an elevated discriminatory value for diagnosis of infectious brain lesions was observed in this sample of patients when the rCBV cutoff value was set to 1.3.

Figure 1. Examples of rCBV maps of neoplastic and infectious lesions.

Glioblastoma multiforme in a 49-year-old man (A,B,C). Axial FLAIR image shows a mass lesion in the right parietal lobe surrounded by infiltrating and vasogenic edema (A), with irregular peripheral enhancement on axial contrast-enhanced T1-W image (B) and increased vascularity on the color-coded rCBV map (C). Metastatic melanoma in an 18-year-old man (D,E,F). Axial FLAIR image depicts a mass lesion in the left parietal lobe with perilesional vasogenic edema (D), irregular peripheral rim enhancement on the axial post-contrast T1-W image (E) and increased vascularity on the color-coded rCBV map (F). Cerebral toxoplasmosis in a 54-year-old woman (G,H,I). Axial FLAIR image shows a mass lesion in the left parietal lobe with surrounding vasogenic edema (G), irregular peripheral rim enhancement on the axial post-contrast T1-W image (H) and hypovascularity on the color-coded rCBV map (I).

Figure 2. rCBV values (x-axis) obtained for each patient are represented as individual points and classified according to the characteristics of the lesions: neoplastic (red squares) or infectious (black dots).

Note that the points corresponding to infectious lesions are mainly concentrated in the lower values of rCBV, whereas the points for the group of neoplastic lesions are more dispersed and show a trend of higher rCBV values.

Figure 3. ROC curve representing the discriminatory capability of rCBV in correctly classifying a lesion as infectious using a cutoff point of 1.3.

The large area under the curve (0.964) indicates the good discriminatory ability of the method.

Figure 4. A cutoff point for rCBV values (x-axis) of 1.3 allows the correct classification (black dots) of all but one infectious lesions and almost all neoplastic lesions; four cases of neoplastic lesions were misclassified as being infectious (red dots).

I = infectious; N = neoplastic.