Answer:

Explanation
1. There is little evidence to support the use of hyperbaric oxygen therapy in radiation necrosis. [Other therapies including anticoagulation and hyperbaric oxygen have been reported in some cases to offer benefit, but there is little evidence to support their use]

2. Studies of bevacizumab therapy in radiation necrosis are limited by short duration of follow-up. [While these studies are encouraging, they are limited by small sample size and a follow-up time of no more than 10 months]

3. Primary CNS lymphoma occurs almost exclusively in immunocompromised patients. [It is typically associated with immunosuppression as in HIV/AIDS, iatrogenic immunosuppression or congenital immunodeficiency. It is extremely rare in the immunocompetent patient.]

4. The asymmetric target sign is the hallmark of cerebral toxoplasmosis. [Toxoplasmosis lesions are usually multiple, may cause mass effect, and their hallmark sign is the asymmetric target sign seen on MRI or computed tomography (CT) where a ring-enhancing abscess contains smaller similarly-enhancing abscesses and eccentric nodules]

5. MRS typically shows elevated lactate and lipids in radiation necrosis with absence of neuro-glial markers, whereas some of these markers are typically increased in neoplasia. [MRS, as in this case, shows a dominant lactate peak, with increased lipids, while other neuro-glial markers (choline, n-acetylaspartate (NAA), creatine) are typically reduced (in radiation necrosis). MRS will show increased lactate if necrosis is present, with decreased NAA and increased choline (in brainstem gliomas and CNS lymphomas).]