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Guan et al. Neuroimmunol Neuroinflammation 2018;5:4 I http://dx.doi.org/10.20517/2347-8659.2017.52 Page 5 of 7

Table 1. CSF cytological syndrome with etiological indication
CSF cytology Clinical syndrome Etiological consideration
Lymphatic inflammation Acute encephalitis Viral encephalitis
Autoimmune encephalitis
Lymphatic inflammation Acute mild or moderated meningism Viral meningitis
Lymphatic inflammation Shepherd with chronic meningitis or Neurobucellosis
chronic encephalomyelitis
Mixed reaction with lymphocyte and neutrophil Recurrent brain-stem encephalitis or Neuro-Behçet disease
diencephalitis
Mixed reaction with lymphocytes and neutrophils Chronic or subacute encephalitis Tubercular meningitis
Cryptococcal meningitis
Mixed reaction with Lymphocytes, eosinophils and Chronic meningitis Neurocysticercosis
plasma cells
Eosinophilic inflammatory Acute meningitis in patients from Angiostrongylus cantonesis
Southeastern China
Lymphatic inflammation with mild increased Acute encephalomyelitis or myelitis Transverse myelitis
eosinophils ADEM
NMOSD

CSF: cerebrospinal fluid; NMDAR: N-methyl-D-aspartate receptor; ADEM: acute disseminated encephalomyelitis; NMOSD: neuromyelitis
optica spectrum disorder

CSF cytology findings in CNS inflammatory disease are relatively non-specific. However, when we consider
the cytological findings under the clinical background of an individual patient, then the so-called “clinical-
CSF cytological syndrome” can lead to a specific diagnosis [Table 1]. For example, in patients with recurrent
CNS midline structure involvement and neutrophil pleocytosis or a mixed cellular response of CSF cytology,
[12]
Neuro-Behçet disease should be highly suspected .

CSF CYTOLOGY OF NEOPLASTIC DISORDERS
Identification of tumor cells by CSF cytology is direct and specific evidence of leptomeningeal involvement
by neoplasms. The appearance of malignant cells in CSF usually indicates generalized seeding of the
leptomeninges by tumor cells. The prevalence of leptomeningeal involvement of different tumors is
important to the cytologists and clinicians to make an accurate clinical-cytoloical conclusion. According to
[13]
Prayson and Fischler , the most commonly identified malignancy in CSF specimens in adults is metastatic
neoplasms. Primary central nervous system neoplasms (e.g. medulloblastoma) account for a higher
percentage of CSF specimens in the pediatric population than in the adult population. We reviewed CSF
[14]
cytology results from PUMCH between 1984 and 2003, including 3922 specimens . Forty-nine cases (1.25%)
were positive for malignant cells. Diagnoses included metastatic tumors (26 cases), metastatic lymphoma/
leukemia (7 cases), primary CNS neoplasms (10 cases) and malignant unclassified neoplasms (6 cases).

Cytology deals with single cells without histological architecture, so cytologists often face the challenge
of arriving at a definitive final diagnosis. Immunocytochemistry and immunophenotyping by flow
[15]
cytometry are helpful for CSF cytology . For example, it was estimated that CSF cytology combined
with immunocytochemistry could indicate diagnostic findings in 50% of cases with primary central
nervous system lymphoma (PCNSL). Flow cytometric analysis (FCA) and polymerase chain reaction
(PCR) of rearranged IgH and TCR genes of CSF are widely used in the diagnosis of PCNSL [16,17] . To
study the diagnostic value of CSF cytology in the diagnosis of PCNSL, we retrospectively analyzed the
[18]
data of 21 patients of PCNSL with positive CSF cytological findings . Conventional CSF cytology,
immunocytochemistry, flow cytometric analysis and PCR of rearranged IgH and TCR genes of CSF
were performed. The clinical and neuroimaging types of 21 patients included meningeal type (n = 13),
parenchymal type (n = 4), ependymal type (n = 3), and optic type (n = 1). The CSF of all the 21 patients
had atypical lymphocytes, suggestive of lymphoma. Of the 20 cases in which immunocytochemistry was
performed, 17 showed B-lymphocyte predominance, which was consistent with the diagnosis of B cell