16
Central Nervous System
meningothelial cells support the interpretation that they are of
hematogenous origin.
Most normal brain and spinal cord elements, such as neurons
and glia, are rarely if ever detected in CSF derived by lumbar
puncture.5 Papillary fragments of cuboidal cells probably origi-
nating in the choroid plexus are, however, occasionally seen.
Because fragments of choroid plexus cannot be reliably distin-
guished cytologically from ependymal cells (Fig. 16.2), these
elements are termed ependymalchoroidal cells by some observ-
ers. Regardless of the histogenesis of these cells in an individual
case, it is important to recognize this normal cellular compo-
nent to avoid mistaking these fragments for neoplasia. Other
normal elements sometimes encountered in CSF obtained by
lumbar puncture are chondrocytes from the intervertebral disk.
The presence of these cells is probably a physical phenomenon
related to direct contact of the sampling needle with the disk
and carries no known pathologic significance. Isolated, benign
spindle-shaped cells are encountered rarely. Although some
observers have considered them to represent astrocytes, others
believe that they are fibroblasts from the loose connective tissue
of the SAS.
Ventricular Fluid
The insertion of ventricular shunts and the introduction of
radiopaque material into ventricles are procedures frequently
performed in patients with hydrocephalus. If a neoplastic con-
dition is suspected, ventricular fluid may be obtained through
the shunt or needle for cytologic evaluation. In a patient with
known meningeal tumor spread, an intraventricular cannula
attached to the Omaya reservoir may be placed to allow installa-
tion of chemotherapeutic agents. Fluid is sometimes withdrawn
through the tube for examination. Ventricular fluids obtained by
this means differ from lumbar puncture-derived CSF in that they
frequently contain choroid plexus cells in large numbers.6 Frag-
ments of normal gray and white matter containing neurons and
glia and portions of capillaries are also often seen (Fig. 16.3).
Recognition that these cell types are characteristic of ventricular
fluids is critical so that they are not misinterpreted as being neo-
plastic in origin.
Infectious Conditions
Increased numbers of inflammatory cells in a sample of CSF,
particularly if a component of polymorphonuclear leukocytes
or enlarged and atypical lymphocytes is observed; suggest
that an infectious process may be present. Although higher
cell counts are more likely to occur if the disorder is occurring
predominantly in the SAS, meningeal infections cannot be
reliably distinguished from meningeal infiltrates secondary to
primary parenchyma disease of the brain or spinal cord. The
composition of the cellular infiltrate may suggest that the proc-
ess in an individual patient is likely to be infectious rather than a
reaction to a noninfectious disorder and may suggest a bacterial,
viral, or fungal etiology. Nevertheless, diagnosis of an infection
requires demonstration of the responsible organism by direct
visualization, culture, or antibody titer.
The most typical cellular presentation of acute bacterial men-
ingitis is an infiltrate composed predominantly of polymorpho-
nuclear leukocytes. This pattern is not specific for this disorder,
Fig. 16.2 Ependymal cells in cerebrospinal fluid (Papanicolaou x HP).
Fig. 16.3 Components frequently seen in ventricular fluids. Gray matter
containing neurons (Papanicolaou x HP).
however, because an acute inflammatory infiltrate can also be
seen in the CSF or acute cerebral infarctions and occasionally in
the early stages of viral and fungal infections.
Key features of acute bacterial meningitis
• Polymorphonuclear leukocyte infiltrate.
Viral meningoencephalitis most frequently produces a pre-
dominantly lymphocytic response in CSF. The cells often show
atypical features, such as clumped chromatin and prominent
nucleoli, and distinguishing between a viral infection and
lymphoma may be difficult.7 The viruses that usually pro-
duce this disorder are the enteroviruses, which do not display
characteristic cellular inclusions in cells of CSF. Other viruses
that involve the parenchyma of the brain and spinal cord and
produce a meningeal infiltrate are cytomegalovirus (CMV),
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