PMC9299438_01
Radiological and histological features of the patient suffering from Erdheim-Chester disease (ECD) at diagnosis. (A) Axial brain MRI showing hyperintense signal in the pons on T2-FLAIR sequence. (B) Axial CT scan showing sheathing of aorta adventitia. (C) Axial CT scan showing bilateral perinephric fat infiltration defined as "hairy-kidney". (D) Axial heart MRI showing a right atrium mass suggestive of a pseudo-tumor. (E) Sagittal 18F fluorodeoxyglucose positron emission tomography demonstrating radiotracer uptake in meta-diaphysis. (F) Histopathological analysis of a CT scan-guided peri-renal adipose tissue biopsy showing massive infiltration by numerous foamy histiocytes and small lymphocytes, with features of cyto-steatonecrosis (HES, magnification x300). (G) Similar biopsy sample with immunostaining showing CD163-positive histiocytes (brown staining, magnification x300). (H) Sample biopsy showing the absence of CD1a-positive cells (brown staining, magnification x300).
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It showed "FLAIR-signal changes" in the pons and upper cerebellum peduncles and a left orbital pseudotumor ( Figures 1 ,  2 ). A whole-body CT scan was performed to rule out cancer and showed bilateral peri-nephric fat infiltration and aortic vascular sheathing ( Figure 1 ).
Radiological brain imaging of the ECD patient at diagnosis. (A) Axial brain MRI showing a hyperintense signal in the pons on the T2-FLAIR sequence. (B) Axial brain MRI showing a hyperintense signal in the pons on the T2-FLAIR sequence. (C) Axial brain MRI showing a slight hyperintense signal on the T2-FLAIR sequence on the upper cerebellum. (D) Axial brain MRI showing left orbital pseudotumor in fat-saturated post-gadolinium T1 imaging. (E) Axial brain MRI showing no signs suggestive of cerebellum atrophy on T2 FLAIR sequence. (F) Axial brain MRI diffuse cortical atrophy predominant in the parietal lobes, with leukoaraiosis (Fazekas grade II) of presumed vascular origin.
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It showed "FLAIR-signal changes" in the pons and upper cerebellum peduncles and a left orbital pseudotumor ( Figures 1 ,  2 ).
Radiological and metabolic evolution of the ECD patient before and after vemurafenib. On the left side of the figure: imaging at ECD diagnosis before specific treatment. From top to bottom: axial brain MRI showing FLAIR change lesions in the pons at ECD diagnosis (upper image). Axial 18F fluorodeoxyglucose positron emission tomography at diagnosis showing radiotracers in the pons (middle image) and in long bones at ECD diagnosis (bottom image). On the right side of the figure: imaging after 8 weeks treatment with vemurafenib. From top to bottom: axial brain MRI showing a decrease in the intensity of the FLAIR signal in the pons after vemurafenib (upper image). Axial 18F fluorodeoxyglucose positron emission tomography after vemurafenib showing a slight decrease of radiotracer uptake in the pons (middle image) and in long bones (bottom image) consistent with partial metabolic response using PERCIST criteria.
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Brain MRI showed partial regression of lesions in the pons. 18FDG-PET showed a decrease in radiotracer uptake in all ECD sites consistent with a partial metabolic response according to PERCIST criteria ( Figure 3 ).