Page 201 - Atlas of Small Animal CT and MRI

Metabolic, Toxic, and Degenerative Disorders 191

Figure 2.5.7 Early‐delayed and Late‐delayed Radiation Effects (Canine) MR

(a) T1+C, TP (b) T2, TP (c) T1+C, TP

(d) T1, TP (e) T2, TP (f) T1+C, TP
10y FS Border Collie with a frontal lobe meningioma that was incompletely surgically excised. A well‐defined, uniformly contrast‐
enhancing extraaxial mass is seen in the region of the left frontal lobe on a preoperative MR examination (a: arrow). On an MR
examination acquired 14 weeks following completion of a course of postoperative radiation therapy (b,c), there is evidence of T2
hyperintensity due to white matter edema in both cerebral hemispheres (b: arrowheads) and in the corpus callosum (b: arrow) with no
evidence of contrast enhancement (c). On a second postoperative MR examination acquired 21 weeks following completion of radiation
therapy (d–f), cerebral T2 hyperintensity has increased and involves both white and gray matter (e: arrowheads). The corpus callosum is
T2 hyperintense and T1 hypointense (d,e: arrow) and appears larger than in the previous examination. There is irregular enhancement in
this region (f: arrow) and in the meninges (f: arrowheads) following contrast administration. Postmortem examination findings were
consistent with delayed radiation effects, including severe encephalomalacia, primarily affecting the white matter, but also extending
into the adjacent gray matter, and lymphocytic perivascular encephalitis located within the cerebrum surrounding the ventricular system.
White matter was necrotic with a neutrophilic inflammatory response. Vessels within the region had fibrinonecrosis of their walls with
some vasculitis and numerous fibrin thrombi.

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