The document discusses primary CNS lymphoma, noting that it refers to lymphoma isolated to the craniospinal axis without primary tumors elsewhere. It can occur in both immunocompetent and immunocompromised patients, with HIV/AIDS being a major risk factor. Presenting symptoms and imaging findings may vary depending on immune status and tumor location, but classic presentations include solitary enhancing masses on MRI, often in deep brain regions. Early diagnosis is important for effective treatment.

2.  Refers to isolated involvement of the craniospinal axis in
the absence of primary tumor elsewhere in the body.
 Once considered a rare occurrence, primary lymphomatous
disease of the CNS is now encountered frequently, in both
immunocompetent and immunocompromised patients.
 HIV infection and AIDS are the leading risk factors and
diagnosis of primary CNS lymphoma in a patient with HIV
is an independent criterion for AIDS.
 Congenital causes of immunodeficiency (e.g., Wiskott-
Aldrich syndrome, IgA deficiency, and X-linked
lymphoproliferative syndrome) and acquired causes,
including an immunosuppressive regimen after organ
transplantation, are also associated with greater risk for
primary lymphoma of the CNS

3.  Primary CNS lymphoma may arise from different
parts of the brain, with deep hemispheric
periventricular white matter being the most
common; corpus callosum, cerebellum, orbits,
and cranial nerves may also harbor the tumor
 After the diagnosis is made, an examination is
done that includes MR imaging of the
craniospinal tract; cerebrospinal fluid and bone
marrow examinations; and screening for primary
tumor in the eye, chest, and abdomen

4.  The presenting symptoms in primary CNS
lymphoma vary depending on the location of the
masses and the immune status of the patient.
 Primary CNS lymphoma in immunocompetent
patients tends to present with a large solitary
hemispheric mass.
 HIV-positive patients often present with an acute
change in mental status and an encephalopathy-
like picture, likely related to combined effects
from other concomitant infections and the side
effects of antiretroviral drugs

5.  Because of the rapid course of primary
lymphoma, a delay in whole brain irradiation
and chemotherapy markedly decreases the
effectiveness of the treatment and survival.
Therefore, early diagnosis is critical.

6.  Systemic lymphoma, on the other hand, may
also present with neurologic symptoms in one
third of patients sometime during the course of
the disease.
 Imaging can distinguish primary CNS
lymphoma from systemic lymphoma; the latter
typically invades dural and leptomeningeal
coverings of the brain.

7.  A high-attenuation lesion on CT and a
periventricular T2 low-signal-intensity mass
with ependymal seeding on MR imaging favor
the diagnosis of primary lymphoma.
 CT, MR imaging, and 201Tl scintigraphy
remain the mainstay in diagnostic imaging
workup of primary CNS lymphoma

8.  In patients with normal immunity, lymphoma
classically presents as a solitary homogeneously
enhancing mass.
 Internal calcification is unusual in CNS
lymphomas unless the patient has undergone
prior chemotherapy or radiation treatment.
 In most patients, MR imaging reveals
intermediate- to low-signal-intensity tumor on
T1-weighted images and either isointense or
hypointense signal relative to the gray matter on
T2-weighted images

9.  Classic findings of a space-occupying lesion,
including mass effect and surrounding
vasogenic edema, are seen on imaging studies.
 After the infusion of paramagnetic contrast
material, intense homogeneous enhancement
(74%) of a solitary mass is the hallmark of
primary CNS lymphoma in immunocompetent
patients.

13.  Unenhanced CT typically shows a high-
density (70%) lesion in a central hemispheric
location, which often reaches or crosses the
midline.
 Highly packed abnormal cells are thought to
be responsible for the increased attenuation.
 Hemorrhage within the tumor is rarely seen,
although it is more common in lymphoma
associated with AIDS.

16.  In more than half (55%) the patients, a
cerebral mass is detected in a supratentorial
parenchymal location with frequent
involvement of the corpus callosum, basal
ganglia, and other deep cerebral nuclei

18.  Contrast enhancement is variable, commonly
of an inhomogeneous or bizarre pattern.
 Solitary ringlike enhancement is more likely
seen in this group

20.  When necrosis develops in the tumor (64%),
the periphery still maintains an isointense
signal and the center becomes hyperintense.
Multiple lesions may be seen in as many as
50% of patients

22.  Extension along the Virchow-Robin spaces is
a well-known feature of primary lymphoma.
 Periventricular lesions frequently invade the
ventricular surface, causing ependymal
seeding (38%)
 However, meningeal enhancement is
surprisingly not frequent.

24.  Although lymphomas are usually hyperdense,
they may also show isodensity or even
hypodensity on CT.
 In the setting of a periventricular low-density
lesion, lymphoma may easily be misdiagnosed
as chronic small vessel ischemia or
encephalomalacia

26.  Diffusely infiltrative lymphomas may not
exhibit parenchymal enhancement at all

28.  The tumor sometimes may show mild
hyperintensity on T1-weighted images.
 Dense cellularity and high nucleus-to-
cytoplasm ratio of the tumor accounts for the
isointense or slightly hypointense signal seen
on T2-weighted sequences.
 Hemorrhage in the tumor also results in low
signal intensity on gradient-echo images
because of magnetic susceptibility.

30.  A rare primary lymphoma of the pineal gland
appears similar to a primary neoplasm of
pineal origin

32.  Cranial nerves, brainstem, cavernous sinus, or
tuber cinereum may have lymphomatous
involvement.
 In general, primary CNS lymphoma in unusual
locations is more common in patients with
AIDS.

36.  In contrast to the large high-attenuation mass in a hemispheric or
central location that is seen in immunocompetent patients,
primary CNS lymphoma in HIV patients may present as a single
lesion or as multiple lesions in deep portions of the brain.
 A necrotic core within the tumor and peculiar enhancement in an
unusual location are also more likely because of HIV-associated
lymphoma.
 Subependymal enhancement should be actively sought on
imaging studies as a potential clue to lymphomatous
involvement.
 Presence of a T2-hypointense component resulting from
increased cellularity should also be noted.
 These imaging features may allow earlier detection of primary
CNS lymphoma and facilitate optimal treatment.