They more often present as seizures than as
mass lesions.
124
Astrocytomas typically present
either with seizures or as a mass lesion, with
headache and increased intracranial pressure.
In other cases, the patients may present with
focal or multifocal signs of cerebral dysfunction.
As they enlarge, astrocytomas may outgrow
their blood supply, resulting in internal areas
of necrosis or hemorrhage and formation of
cystic components. Impairment of conscious-
ness is usually due to compression or infiltra-
tion of the diencephalon or herniation. Surpris-
ingly, primary brainstem astrocytomas, which
are typically seen in adolescents and young
adults, cause mainly impairment of cranial
motor nerves while leaving sensory function
and consciousness intact until very late in the
course.
Primary CNS lymphoma (PCNSL) was once
considered to be a rare tumor that was seen
mainly in patients who were immune suppres-
sed; however, PCNSL has increased in frequ-
ency in recent years in patients who are not im-
mune compromised.
123,125
The reason for the
increased incidence is not known. PCNSL be-
haves quite differently from systemic lympho-
mas.
122
The tumors invade the brain much like
astrocytic tumors. They often occur along the
ventricular surfaces and may infiltrate along
white matter tracts. In this respect, primary
CNS lymphomas present in ways that are sim-
ilar to astrocytic tumors. However, it is unusual
for a primary CNS lymphoma to reach so large
a size, or to present by impairment of con-
sciousness, unless it begins in the diencephalon.
Metastatic tumors are most often from lung,
breast, or renal cell cancers or melanoma.
121
Tumors arising below the diaphragm usually
do not invade the brain unless they first cause
pulmonary metastases. Unlike primary brain
tumors, metastases rarely infiltrate the brain,
and can often be shelled out at surgery. Meta-
static tumors usually present either as seizures
or as mass lesions, and often enlarge quite
rapidly. This tendency also results in tumors
outgrowing their blood supply, resulting in in-
farction and hemorrhage (see previous section).
The ease of removing metastatic brain tu-
mors has led to some controversy over the
optimal treatment. Patients who have solitary
metastatic tumors removed on average survive
longer than patients who are treated with cor-
ticosteroids and radiation.
126
Occasional pa-
tients with lung cancer may have long-term
survival and even apparent cure has been re-
ported after removal of a single brain metas-
tasis as well as the lung primary tumor. Pa-
tients with brain tumors frequently suffer
from seizures, but prophylactic administration
of anticonvulsants has not been found to be of
value.
127
Small, surgically inaccessible metas-
tases can be treated by stereotactic radio-
surgery.
128
Brain Abscess and Granuloma
A wide range of microorganisms, including
viruses, bacteria, fungi, and parasites, can in-
vade the brain parenchyma, producing an acute
destructive encephalitis (see page 156). How-
ever, if the immune response is successful in
containing the invader, a more chronic abscess
or granuloma may result, which may act more
as a compressive mass.
A brain abscess is a focal collection of pus
within the parenchyma of the brain. The in-
fective agents reach the brain hematogenously
or by direct extension from an infected con-
tiguous organ (paranasal sinus, middle ear).
129
Most bacterial brain abscesses occur in the
cerebral hemispheres, particularly in the fron-
tal or temporal lobes. In many countries in
Central and South America, cysticercosis is the
most common cause of infectious mass lesions
in the cerebral hemispheres. However, cysti-
cercosis typically presents as seizures, and only
occasionally as a mass lesion.
130
In countries in
which sheep herding is a major activity, echino-
coccal (hydatid) cyst must also be considered,
although these can usually be recognized because
they are more cystic in appearance than ab-
scesses on CT or MRI scan.
131
Patients with
HIV infection present a special challenge in the
diagnosis of coma, as they may have a much
wider array of cerebral infectious lesions and
are also disposed to primary CNS lymphoma.
However, toxoplasmosis is so common in this
group of patients that most clinicians begin with
2 weeks of therapy for that organism.
132
When
the appearance on scan is unusual, though,
early biopsy is often indicated to establish the
cause of the lesion(s) and optimal mode of
treatment.
Other organisms may cause chronic infec-
tion resulting in formation of granulomas that
Specific Causes of Structural Coma
141
may reach sufficient size to act as a mass lesion.
These include tuberculomas in tuberculosis,
torulomas in cryptococcal infection, and gum-
mas in syphilis.
Because the symptoms are mainly due to
brain compression, the clinical symptoms of
brain abscess are similar to those of brain neo-
plasms, except they usually evolve more rapidly
(Table 4–6).
Headache, focal neurologic signs, and sei-
zures are relatively common. Fever and nuchal
rigidity are generally present only during the
early encephalitic phase of the infection, and
are uncommon in encapsulated brain abscesses.
The diagnosis may be suspected in a patient with
a known source of infection or an immunosup-
pressed patient.
On imaging with either CT or MRI, the en-
hanced rim of an abscess is usually thinner and
more regular than that of a tumor and may be
very thin where it abuts the ventricle, some-
times leading to ventricular rupture (Figure
4–7). The infective nidus is often surrounded by
more vasogenic edema than usually surrounds
brain neoplasms. Diffusion-weighted images
indicate restricted diffusion within the abscess,
which can be distinguished from the cystic ar-
eas within tumors, which represent areas of
infarction. The presence of higher levels of
amino acids within the abscess on magnetic
resonance spectroscopy (MRS) may also be
helpful in differentiating the pathologies (Table
4–7).
If the lesion is small and the organism can
be identified, antibiotics can treat the abscess
successfully. Larger lesions require drainage or
excision.
INFRATENTORIAL COMPRESSIVE
LESIONS
The same mass lesions that affect the supra-
tentorial space can also occur infratentorially
(i.e., in the posterior fossa). Hence, while both
the focal symptoms caused by posterior fossa
masses and the symptoms of herniation dif-
fer substantially from those of supratentorial
masses, the pathophysiologic mechanisms are
similar. For that reason, we will focus in this
section on the ways in which posterior fossa
compressive lesions differ from those that oc-
cur supratentorially. Depending on the site of
the lesion, compressive lesions of the posterior
fossa are more likely to cause cerebellar signs
and eye movement disorders and less likely
to cause isolated hemiplegia. Herniation may
be either downward as the cerebellar tonsils
are forced through the foramen magnum or
upward as the cerebellar vermis pushes the up-
Table 4–6 Presenting Signs and
Symptoms in 968 Patients With
Brain Abscess
Sign or Symptom
Frequency
Range
Mean
Headache
55%–97%
77%
Depressed consciousness
28%–91%
53%
Fever
32%–62%
53%
Nausea with vomiting
35%–85%
51%
Papilledema
9%–56%
39%
Hemiparesis
23%–44%
36%
Seizures
13%–35%
24%
Neck stiffness
5%–41%
23%
From Kastenbauer et al.,
133
with permission.
Figure 4–7. A 49-year-old man with AIDS was admitted
for evaluation of headache, nausea, and bilateral weak-
ness and intermittent focal motor seizures. MRI showed
multiple ring-enhancing lesions. Note that the smooth,
contrast-enhancing wall of this right parietal lesion is typ-
ical of an abscess. He was treated with broad spectrum
antibiotics and improved.
142
Plum and Posner’s Diagnosis of Stupor and Coma