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cally important for preventing further morbidity or mortality of these serious compli-
cations. Subdural hematoma, is one of the most common cerebrovascular complications
post-HSCT detected by CT. Thus CT scan is a rapid modality of radiological proce-
dures which gives immediate answers for appropriate treatment decisions.
3.2.2 Positron Emission Tomography (PET)/Magnetic
Resonance Imaging (MR)
The roles of Positron Emission Tomography and Magnetic Resonance Imaging are
critical in the late post-transplantation period (>100 days) when complications such
as avascular necrosis and secondary malignancies become more important, but both
radiographic technologies are of significance earlier as well [ 1 , 5 , 6 ].
Central Nervous System (CNS) infections can be caused by a variety of organisms
with findings that can be well demonstrated on MR, such as enlargement of the ven-
tricular or subarachnoid spaces in opportunistic infections, and abscesses or granulo-
mas with or without ring enhancement. Aspergillosis seen on T2-weighted MR images
can show areas of intermediate signal intensity that have peripheral rings of hyperin-
tensity. It is important to note that ring-like enhancement correlates with a less inva-
sive form of disease, suggesting host immune response. Herpes virus infections may
also be diagnosed on MR. Herpes encephalitis can lead to white matter demyelination,
as well as, changes in signal intensity of the temporal lobes. In the case of HHV-6
infection, MR shows increased temporal lobe signal intensity on T2-weighted images
and increased hippocampal glucose uptake on PET scan. Epstein Barr Virus (EBV)
infection has been demonstrated on MR as focal infarcts with rim-like enhancement.
Toxicity from immunosuppressive therapies, such as cyclosporine, may present
as posterior reversible encephalopathy syndrome (PRES), which on MR imaging of
the brain shows up as symmetrically distributed areas of vasogenic edema in the
areas supplied by the posterior circulation (Fig. 3.8). Other findings include focal
gray and white matter changes, watershed vascular injuries, and/or central pontine
myelinolysis. This differs from the MR findings seen in patients with encephalopa-
thy due to the conditioning regimen prior to transplant and/or radiation therapy, as
one will usually see widespread focal deep white matter and periventricular white
matter changes, leukoencephalopathy, and diffuse cerebral atrophy depending on
the time elapsed since HSCT [ 1 ].
After HSCT, bone mineral density is decreased. This combined with a multitude
of other factors, including but not limited to corticosteroid exposure, irradiation,
and inactivity combine to place the transplant recipient at risk for avascular necro-
sis, particularly of the hips and knees. While a plain radiograph is likely to be the
first test obtained in assessing for avascular necrosis, MR is more sensitive and is
endorsed for yearly screening in this at-risk population [ 1 ]. As MR can lead to ear-
lier detection, it also allows for earlier intervention in the patients in whom the
beginning signs of avascular necrosis are detected. Avascular necrosis on MR
shows up as heterogeneous signal intensity changes that may involve collapse of
M. Atiq et al.