Diagnostic cytology
Fig. 16.11 Small undifferentiated malignant tumor cells of medulloblastoma in cerebrospinal fluid ((A) Papanicolaou xHP; (B) immunoperoxidase stain
using an antibody against N-CAMxHP).
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cell tumors and the primary pineal tumor, the pineoblastoma,
behave in a similar manner.72
Although the majority of primary brain tumors that spread in
the CSF are histologically malignant and biologically aggressive,
choroid plexus tumors of all grades, ranging from the choroid
plexus papilloma to the choroid plexus carcinoma, exhibit this
behavior. This pattern of spread is undoubtedly because of the
location of these tumors in the ventricles with ready access to
the CSF, as well as the friable, papillary nature of the tissue.
The morphology of these papillary fronds is usually sufficiently
characteristic to allow diagnosis of these tumors.2 The malignant
variety is cytologically similar to metastatic papillary adenocar-
cinoma, but the extremely young age of afflicted infants with
the typical large, intraventricular masses produced allows this
distinction to be readily made.
Fig. 16.12 Needle aspirate of germinoma (H&E x MP).
Diagnostic Accuracy in Cerebrospinal
Fluid Cytology
slow growing, the most malignant variety of astrocytic glioma,
glioblastoma multiforme, is capable of disseminating in the
SAS. This pattern of behavior is particularly characteristic of
malignant brainstem gliomas. These cells are frequently small
and anaplastic in their cellular characteristics, making them dif-
ficult to distinguish from other small-cell neoplasms, such as
medulloblastoma and ependymoblastoma. Precise localization
of the primary tumor in the brainstem as opposed to the fourth
ventricle or cerebellum is helpful in making this distinction. In
addition, the expression of large amounts of GFAP, although
characteristic of gliomas, is unusual in medulloblastomas.
Key features of medulloblastoma
• Clusters and single cells;
• Scant cytoplasm;
• High N/C ratio; and
• Hyperchromatic nuclei.
Another group of childhood tumors that are relatively uncom-
mon but that share the tendency to disseminate through spinal
fluid pathways are tumors of the pineal gland and hypothalamic
region.71 The germinoma is the tumor type most notorious for
CSF spread (Fig. 16.12), but the other types of malignant germ
Because biopsy of the meninges is rare, the only data about the rate
of false-negative cases of CSF are derived from autopsy findings.
Glass and associates observed that the likelihood of obtaining
positive CSF findings in patients with meningeal dissemination
is directly proportional to the extent of meningeal disease.47 Thus,
malignant cells are detected in about a third of patients with only
focal meningeal infiltration, whereas approximately two-thirds
of cases of diffuse meningeal carcinomatosis can be detected
cytologically.47 Olson and associates also point out that multiple
examinations of CSF increase the overall rate of detection to 80%
of cases, presumably because of better sampling.52
A series of 225 samples of CSF reported by Bigner and
Johnston had a false-positive rate of 5 in 225.49 Cases of false-
positive diagnoses include:
(1 )
A case of herpes meningoencephalitis misinter-
preted as adenocarcinoma;
(2 )
A case that probably represented cross-contamina-
tion of a filter with adenocarcinoma from another
A case in which a filter containing reactive meso-
thelium from an effusion was mislabeled as CSF
and misinterpreted as adenocarcinoma;
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