Diagnosing central nervous system (CNS) lymphoma remains a challenge. Most patients have to undergo brain biopsy to obtain tissue for diagnosis, with associated risks of serious complications. Diagnostic markers in blood or cerebrospinal fluid (CSF) could facilitate early diagnosis with low complication rates.
In a retrospective study of patients with Primary central nervous system lymphoma (PCNSL) treated between January 2001 and December 2011 at the Navy General Hospital (Beijing). All included patients were pathologically diagnosed with PCNSL. Specimens were obtained by stereotactic biopsy and diagnosed by pathological examination. Serological panel had to be negative for HIV.
Out of the 118 patients, 73 (61.9%) were male and 45 (38.1%) were female. Median age was 54 (range 11-83) years. All patients had B cell lymphoma. The lesions showed slightly hyperdense shadows on computed tomography (CT) images, and mostly hyperintense T1 and iso- or hyperintense T2 signals on magnetic resonance imaging (MRI). Most lesions showed patchy enhancement after enhanced scanning, and some had the characteristic “butterfly sign” on enhanced MRI. The magnetic resonance spectroscopy of PCNSL manifested as increased Cho peak, moderately decreased NAA peak, and slightly decreased Cr peak. Positron emission tomography indicated high metabolism of 18F-FDG in PCNSL lesions.
MRI is important in the diagnosis of PCNSL. Understanding the imaging features of PCNSL will help improve its diagnosis in clinics 1).
van Westrhenen et al., performed a systematic review literature search for studies on markers in blood or cerebrospinal fluid for the diagnosis CNS lymphoma and assessed the methodological quality of studies with the Quality Assessment of Diagnostic Accuracy Studies tool (QUADAS-2).
They evaluated diagnostic value of the markers at a given threshold, as well as differences between mean or median levels in patients versus control groups. Twenty-five studies were included, reporting diagnostic value for 18 markers in CSF (microRNAs -21, -19b, and -92a, RNU2-1f, CXCL13, interleukins -6, -8, and -10, soluble interleukin-2-receptor, soluble CD19, soluble CD27, tumour necrosis factor-alfa, beta-2-microglobulin, antithrombin III, soluble transmembrane activator and calcium modulator and cyclophilin ligand interactor, soluble B cell maturation antigen, neopterin and osteopontin) and three markers in blood (microRNA-21 soluble CD27, and beta-2-microglobulin). All studies were at considerable risk of bias and there were concerns regarding the applicability of 15 studies. CXCL13, beta 2 microglobulin and neopterin have the highest potential in diagnosing CNS lymphoma, but further study is still needed before they can be used in clinical practice 2).
Radiographic features
The most helpful imaging pattern presents mainly in untreated non-immunocompromised patients is of a CT hyperdense avidly enhancing mass, with MRI T1 hypointense, T2 iso- to hypointense, vivid homogeneous gadolinium-enhancing lesion/s with restricted diffusion, subependymal extension, and crossing of the corpus callosum. Unfortunately, this pattern is not always present.
Typically PCNSL are supratentorial (75-85%) and appear as a mass or multiple masses (11-50%) that are usually in contact with the subarachnoid/ependymal surfaces. Crossing the corpus callosum is not infrequently seen. Enhancement on both CT and MRI is pronounced and usually homogeneous. Even with larger lesions, there is little mass effect for size and limited surrounding vasogenic oedema.
Low-grade tumours differ from the more common high-grade PCNSL in several ways:
Deep locations and spinal involvement is more common
Contrast enhancement is absent, irregular or only mild
Disseminated meningeal/intraventricular disease is uncommon, it is seen in ~5% (range 1-7%) of cases at presentation and usually in high-grade cases.
It should be noted that in patients who are immunocompromised (typically HIV/AIDS or post-transplant) appearances are more heterogeneous, including central non-enhancement/necrosis and haemorrhage, although the latter is still uncommon
CT
Most lesions are hyperattenuating (70%) 3
Shows enhancement
Haemorrhage is distinctly uncommon
There are often multiple lesions in patients with HIV/AIDS
MRI
Scintigraphy
Flow cytometry
Flow cytometry has a high specificity and can confirm the diagnosis of a lymphoma significantly faster than immunohistochemistry. This allows for rapid initiation of treatment in this highly aggressive tumor. However, since its sensitivity is less than 100%, van der Meulen et al., recommend to perform histology plus immunohistochemistry in parallel to flow cytometry 4).