Most patients of our series showed patchy contrast enhancement. Bakshi et al. [
2] defined cases of LC as diffuse white matter infiltration without the formation of discrete mass lesions and with little contrast enhancement. Rollinset al. [
12]reviewed the pathological findings of LC. In LC, there is a diffuse pattern of brain infiltration coupled with the associated perivascular cuffing by both lymphoma cells and non-neoplastic lymphocytes that can mimic an encephalitic pattern [
2]. The common reason for a lack of contrast enhancement on MRI is assumed to be an intact blood-brain barrier (BBB), or that significant BBB disruption by lymphoma cells is not yet produced [
14]. However, subtle or patchy contrast enhancement has been described in some cases [
6,
7]. In these cases, biopsy revealed tumor cells that induced subtle contrast enhancement distributed throughout the white matter; the atypical cells were neither cohesive nor did they form a mass [
3]. Subtle patchy contrast enhancement was found in 3 of our 7 patients and 2 patients showed multiple patchy. Our Case 5 showed more substantial contrast enhancement in both cerebral hemispheres, which was misdiagnosed with encephalitis based on the initial MRI and improved after steroid treatment. Histopathological analysis of this patient revealed severe tumor cell infiltration with small round lymphatic cells cuffing and destroying microvasculature, which is consistent with the imaging finding of multi-focal patchy contrast enhancement due to BBB disruption. Delayed scanning post-contrast T1WI was 20 min after the initial scan and showed marked contrast enhancement (Figure
3). Other reports [
4,
15] have reported that contrast enhancement patterns can change in LC patients on follow-up MRI. A systematic review LC patients found that 26.6% of those without contrast enhancement on the initial MRI and 16.6% of those who showed patchy contrast enhancement eventually developed nodular contrast enhancing lesions at follow-up imaging [
5]. The transformation from a non-enhancing to enhancing lesion reflects the eventual disruption of the BBB [
16]; this is likely a late event that is due to factors at the cellular level [
17]. Although the reason for this transformation remains unclear, we speculate that LC without contrast enhancement might be an early-stage appearance of this specific type of PCNSL with diffuse infiltrating neoplastic cells.