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5  Imaging the Intraoperative and Postoperative Brain

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5.2.4\ Chemotherapy Wafers

5.2.4.1\ Discussion

Chemotherapy wafers, such as carmustine implants (Gliadel), are sometimes implanted in the surgical bed after malignant brain neoplasm resection. The wafers are biodegradable sheets of polymers that are impregnated with the chemotherapy agent. Initially, the wafers appear as hypointense linear structures on T1and T2-weighted MRI sequences, but they can change in signal intensity characteristics over time (Fig. 5.28).

a

c

The presence of wafers does not alter the pattern of tumor recurrence. Perfusion MRI is particularly­ useful to monitor the treatment effects and differentiate these from recurrent neoplasm. The presence of foci with elevated CBV suggests tumor recurrence. MR spectroscopy can also be useful for monitoring tumor response to chemotherapy wafers. For example, it has been noted that increased peritumoral NAA/Cr and decreased peritumoral Cho/NAA compared with normal brain tissue by 3–5 weeks suggest treatment response.

b

Fig. 5.28  Chemotherapy wafers. The patient has a his-

tion cavity (arrows). T2-weighted (b) and axial

tory of glioblastoma status post resection and implanta-

T1-weighted (c) MR images obtained 1 day after surgery

tion of Gliadel wafers.Axial CT (a) shows hyperattenuating

demonstrate the low signal linear Gliadel wafers (arrows)

linear structures along the edges of the right frontal resec-

lining the resection cavity