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A 79-year-old man presented to the ED with weakness, anorexia,
and lethargy of two day’s duration. His next door neighbor
called for an ambulance.
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In the ED, he complained of a mild headache, but did not have
abdominal pain, vomiting, diarrhea, cough, or urinary symptoms.
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On examination, he
was an elderly man who was lethargic and oriented only to person
and place. His verbal responses and responses to simple commands
were slow. His vital signs were normal aside from a temperature
of 100.9°F (rectal).
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His pupils were equal and reactive and extraocular motion was
normal. Funduscopic examination was limited by cataracts. His neck
was supple. His heart, lung, and abdominal examinations were normal.
Neurological examination revealed normal strength, sensation, and
reflexes in all extremities.
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Given the patient’s low-grade fever without an identified
source, slowed mentation and complaint of headache, meningitis was
a diagnostic consideration. Because his fundi could not be visualized,
a noncontrast head CT was performed prior to lumbar puncture (Figure
1).
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- There is no midline shift or mass effect.
- Is it safe to perform a lumbar puncture?
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(NB. Because the CT slice orientation was not parallel to the
skull base, the anterior portions of the lower slices (8–10)
extend into the orbits.)
++
++
Intracranial lesions causing mass effect are important to identify
prior to performing a lumbar puncture (LP) in patients suspected
of having meningitis because they increase the risk of post-LP herniation.
The risk of herniation is greatest when a mass causes unequal pressure
between intracranial compartments.
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Although contrast CT is better than noncontrast at detecting
intracerebral masses such as tumors and abscesses, a lesion that
is causing significant mass effect can usually be detected on a
noncontrast scan. Therefore, noncontrast CT is generally felt to
be an acceptable means of excluding an intracranial mass prior to
LP.
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In this patient’s CT, there is no evident distortion
of brain parenchyma and no midline shift. However, a sizable intracranial
mass is present. Had the patient undergone lumbar puncture, fatal
herniation would have been the likely outcome.
++
This patient’s CT is notable for ventricular
enlargement (Figure 2). Ventricular enlargement is an expected
finding in elderly patients and is usually due to cerebral atrophy (loss of brain tissue). Atrophy
is also termed ex-vacuo hydrocephalus.
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