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Usefulness of the multimodality imaging for the diagnosis of an atypical lymphoma of the brainstem ATTIA M, KOUKI S, LANDOULSI M,BOUGUERRA S,AROUS Y, BOUJEMAA H, BEN ABDALLAH N NEURORADIOLOGY : NR 17 INTRODUCTION Primary central nervous system lymphoma(PCNSL) is a rare tumor, making up only 1%-1.5% of all cranial tumors. They occur sporadically or in association with congenital or acquired immunodeficiency disorders. the diagnosis of primary central nervous system lymphoma should always be considered as an emergency because of the therapeutic consequences it implies. There were reports that 55% of PCNSL occurred at supratentorial corpus callosum and cerebral white matter around the ventricles and 17% occurred at basal ganglia, thalamus, and subthalamus region, while only 11% were located at posterior cranial fossa. The case we report here illustrates the contribution of MRS in the diagnostic approach of a very atypical PCNSL of the brainstem. Material and Method We report the case of a 24-year-old male with no significant medical history presented with swallowing disorder, fever, irregular breathing and cerebellar syndrome. The patient had a brain MRI with the conventional sequences and a multimodal imaging including diffusion and spectroscopy sequences. Sagittal T2-weighted MRI Diffuse hyperintensity on T2-weighted images and flair involving the pons and extending to the bulb Axial FLAIR –weighted MRI axial T2-weighted MRI T1-weighted axial images before and after intravenous contrast administration : ring enhancement of the lesions The mass lesion shows hyperintensity on DWI On ADC map, the solid lesions are hypointenses. Single-voxel 1H MRS TE(30 ms) Single-voxel 1H MRS TE(135ms) Single-voxel 1H MRS examination shows a decrease of the NAA peak (2.0 ppm), an increase of the choline peak (3.2 ppm),and a lipid peak (1.3 ppm). Lumbar puncture for cerebrospinal fluid (CSF) cytological examination detected B lymphoid cells, the diagnosis of PCNSL was later confirmed by a brain biopsy. DISCUSSION The incidence of primary central nervous system lymphomas(PCNSL) , aggressive neoplasms with an indeterminate pathogenesis, is increasing in immunocompetent and immunocompromised patients. They currently represent 6.6–15.4% of all primary brain tumors. They are comprised of non- Hodgkin’s lymphoma, mostly of B-cell origin, and may appear as solitary or multiple nodular tumors, or as diffusely infiltrative perivascular neoplasms . DISCUSSION 80% of primary CNS lymphomas locate in the supratentorial region, while 11% of the cases involve the posterior cranial fossa, and are mainly in the cerebellum. Optimal management of primary CNS lymphoma requires a correct diagnosis, since steroids may alter or even eliminate the ability to obtain histological diagnosis. large B cell lymphoma is highly responsive to radiotherapy and steroid, causing complete regression and clinical remission. In addition, chemotherapeutic agents can cross the impaired blood-brain barrier, leading to complete response to chemotherapy in some patients. Nevertheless, the tumor may recur in 80–95% of cases Imaging in immunocompetent patients PCNSL is typically a solitary and supratentorial lesion. In a study of 100 immunocompetent patients with PCNSL, the most common locationwas the cerebral hemispheres seen in 38% of cases. Less commonly the cerebellum and brainstem may be infiltrated. Contrast-enhanced magnetic resonance imaging (MRI) is the optimal imaging technique.22 PCNSL is typically isohypointense on T1-weighted imaging. It is isohypointense to grey matter on T2-weighted imaging PCNSL can also demonstrate T2-weighted hyperintensity. Contrast enhancement tends to be homogeneous. In immunocompetent patients, necrotic, thus ring-enhancing, lesions are rare. Imaging in immunocompromised patients Some features are more typical in the immunocompromised population. Here, multiple lesions are more common and seen in up to 60% of patients,25 a higher percentage than the 38% found in immunocompetent patients. These lesions also tend to be smaller. PCNSL in the immunocompromised demonstrates rapid growth. The tumour outstrips its blood supply and becomes necrotic centrally. This leads to ring enhancement after the administration of contrast medium. The ring-like enhancement may be irregular and nodular Advanced imaging techniques DIFFUSION The effect of diffusion-weighted imaging (DWI) is based on the diffusion of water molecules. Diffusion-weighted imaging is a kind of modern molecular imaging and gives a picture of molecular motion. It is based on Brownian motion of water molecules and thus provides information on the mobility of water molecules. Cellular relatively dense packed and organized tissue as cerebral cortex restricts movement and diffusion of water molecules. DIFFUSION DWI provides useful additional information about tissue characterization, and may be helpful to differentiate CNS lymphomas from other cerebral neoplasms. Water diffusion is often restricted in lymphoma as it is hypercellular and made up of large lymphoid cells. PCNSL is therefore hyperintense on diffusion-weighted imaging (DWI) and hypointense on apparent diffusion coefficient (ADC) maps (low ADC values). Ninety percent of pre-treatment patients in one study demonstrated restricted diffusion, but PCNSL may also demonstrate unrestricted diffusion. After treatment, restricted diffusion is more variable. Spectroscopy 1H-magnetic resonance spectroscopy (MRS) provides information on metabolic change in vivo. PCNSL cases demonstrates raised choline (Cho) resonances relative to creatine (Cr) and N-acetyl aspartate (NAA), which are non-specific and are also demonstrated in other brain tumors. Spectroscopy The most specific finding for PCNSL on MRS is an increase in lipid resonance. This is typically a signature of cell death; however, a lipid dominated spectrum is found in PCNSL that is not macroscopically necrotic. This appears to be due to numerous macrophages and the increased turnover of membrane components in transformed lymphoid cells. PERFUSION the maximum rCBV ratios is often less than 2.3. Contrary to the strong enhancement, the maximum rCBV ratios of CNS lymphomas were significantly lower than those of high grade gliomas, metastases, or meningiomas. Strong enhancement without CBV increment in lymphoma is attributed to the blood brain barrier destruction without neovascularization in contrast to the marked contrast enhancement with increased vascularity in high grade gliomas. CONCLUSION PCNSL may present with a wide range of established imaging findings. This makes diagnosis with imaging alone challenging. Additionally, the radiologist needs to be aware of the rare PCNSL variants that present with their own unique imaging features. Much interest has been placed on advanced imaging techniques, including MR perfusion, MRS, and nuclear medicine, to aid diagnosis. Their findings have been shown to complement conventional MRI findings, supporting a diagnosis of PCNSL References Imaging of primary central nervous system lymphoma. Y.Z. Tang et al. Clinical Radiology 66 (2011) 768-777. Analysis of perfusion weighted image of CNS lymphoma. In Ho Lee and al. European Journal of Radiology 76 (2010) 48–51. Diffusion-weighted imaging of primary brain lymphomas: Effect of ADC value and signal intensity of T2-weighted imaging. Masuma Akter and al. Computerized Medical Imaging and Graphics 32 (2008) 539–543. Conventional MRI and 1H MR spectroscopy in primary central nervous system lymphoma. Stefan Martin Golaszewski. European Journal of Radiology Extra 74 (2010) e5–e8.
