Magnetic resonance in neuro-oncology: Achievements and challenges - Signal Processing in MRS with Biomedical Applications - page 259

giomas, with alanine being rarely seen in nonmeningeal tumors. However,
mean alanine concentrations were lower in eight patients with meningiomas
compared to those of six patients with metastatic brain lesions in a study by
Howe et al. [263]. An alanine peak was also observed in each of three patients
with central neurocytomas who underwent proton MRS [264].

Besides alanine, the appearance of glutamine - glutamate in the spectral
region between 2.1 ppm and 2.55 ppm is also described as “highly sugges
tive of meningioma” [211]. In Ref. [144], increased glutamine - glutamate
was detected in twelve of the nineteen patients with meningiomas, but this
was also found in four of eight patients with metastatic brain tumors, though
in none of the patients with Schwannomas. Majos et al. [262] reported in
creased glutamine - glutamate in the patients with meningiomas compared
to astrocytomas. These authors found that, in addition to alanine, glutamine
- glutamate was the best metabolite for distinguishing patients with menin
giomas from those with primitive neuroectodermal tumors. Opstad et al.
[145] found that six patients with meningiomas had elevated glutamine - glu
tamate concentrations compared to six patients with astrocytomas as well as
in comparison to normal white matter. The reduced glutathione resonance
at 2.9 ppm was also significantly greater in the patients with meningioma
compared to those with astrocytomas, as well as in the normal white matter
in Ref. [145]. Some authors [144, 262, 265] have used various combinations
of metabolites to identify meningiomas, with the presence of alanine and glu
tamine - glutamate usually playing an important role.

8.1.4.2 Distinguishing primary brain tumors from brain metas-

tases

Another clinically important distinction that has been aided by MRSI is be
tween primary brain tumors and metastatic lesions. Again, morphologic char
acteristics are often su cient to distinguish these entities, but when this is
not the case, MRSI has sometimes been helpful. The most consistent distinc
tion is in the peritumoral region. Since the peritumoral region of metastatic
lesions is typically comprised of vasogenic edema rather than cellular infiltra
tion, choline is usually low in the area surrounding metastases. On the other
hand, elevated choline in the peritumoral region is suggestive of a primary
brain tumor [211]. Fan et al. [235] reported significantly lower cholineto
creatine ratios in the peritumoral region in eight patients with brain metas
tases compared to fourteen patients with highgrade gliomas. These authors
consider infiltration of adjacent brain parenchyma a unique feature of high
grade glioma. Similar findings have been reported by Law et al. [266]. A
different pattern was reported, however, by Ricci et al. [267] in their study of
thirteen patients with intracerebral tumors. The perilesional edema showed
normal choline to creatine ratios. Included in this series were seven patients
with glioblastomas.