A. Dobbeleir

Sensitivity and specificity of thallium-201 single-photon emission tomography in the functional detection and differential diagnosis of brain tumours

The aim of this retrospective study was to assess the contribution of thallium-201 single-photon emission tomography (SPET) in the detection and differential diagnosis of brain tumours. In 90 patients 201Tl SPET was performed because of clinical or radiological suspicion of tumoral invasion, completed by technetium-99m hexamethylpropylene amine oxime and 99mTc-sestamibi SPET in some patients. For all tumours, diagnosis was based on biopsy or autopsy. Other diagnoses were made only after clinical and radiological follow-up for at least 6 months. Histologically tumours consisted of astrocytoma stage I or II (number of patients, n=6), astrocytoma stage III (n=8), glioblastoma multiforme (n=14) and oligodendroglioma (n=3), brain metastasis (n=14), lymphoma (n=3), meningioma (n=3), pituitary adenoma (n=2), pineal tumour (n=1), colloid cyst (n=1) and craniopharyngioma (n=1). False-negative studies included pineal tumour (n=1), colloid cyst (n=1), craniopharyngioma (n=1), astrocytomas stage I or II (n=6) and stage III (n=3), oligodendroglioma (n=2) and metastasis in the brain stem (n=1). Additional metastases approximately < 1.5 cm were not detected in two patients and 201Tl SPET underestimated tumoral extent in one patient suffering from glioblastoma multiforme (n=1). A false-positive study was obtained in a patient with skull metastasis (n=l). All 15 patients who were finally shown to suffer from ischaemic infarction had a normal SPET study 9–28 days after the onset of symptomatology. Of five patients with haemorrhagic infarction, studied within 2 weeks, four were false-positive. Of six patients with intracranial haemorrhage, studied 9–39 days later, one showed focal 201Tl accumulation. Two further false-positive studies consisted of angioma and epidural haematoma. Finally, SPET studies were normal in six patients with definite diagnosis of (reactive) gliosis (n=3), Binswangers encephalopathy (n=1), postinfectious encephalopathy (n=1) and multiple sclerosis (n=1). In the patient population presented, sensitivity of 201Tl SPET for supratentorial brain tumours was 71.7% and specificity was 80.9%. Clinical information and control SPET studies in combination with early, 30-min and 3- to 4-h delayed imaging may be expected to improve on these figures. On the other hand it seems that, in addition to tumoral histology, the presence of tumours in the fossa posterior and small volumes contribute to the occurrence of falsenegative 201Tl SPET studies.

APRAXIC AGRAPHIA FOLLOWING A RIGHT CEREBELLAR HEMORRHAGE

Apraxic agraphia follows disruption of skilled movement plans of writing and is characterized by distorted, hesitant, incomplete, and imprecise letter formation. The causative lesion is located in the superior parietal lobe (storage of graphomotor plans) or the dorsolateral and medial part of prefrontal cortex (conversion of graphomotor plans to motor commands).1 Recently, the condition was also reported after left dorsomedial thalamic infarction with reduced oxygen metabolism in left premotor areas.2 ### Case report. A 72-year-old right-handed engineer acutely developed postural instability and gait disturbances. Neurologic examination showed a pure cerebellar deficit with distinct midline cerebellar dysfunction and less pronounced right appendicular ataxia. Apart from implantation of a pacemaker for sick sinus syndrome, his medical history was unremarkable. CT scan of the brain disclosed a hemorrhagic lesion in the right cerebellar hemisphere involving cortex and the medullary core (figure 1A). No supratentorial lesions were detected by repeat CT at 3 and 6 months after onset. Figure 1 CT scan and quantified Tc-99m-ethyl cysteinate dimer SPECT studies CT scan of the brain disclosing a hemorrhage in the right cerebellar hemisphere involving cortex and the medullary core (A). Quantified Tc-99m-ethyl cysteinate dimer SPECT studies conducted …

Sensitivity and specificity of 99Tcm-HMPAO single-headed SPECT in dementia.

The sensitivity and specificity of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) single-headed single photon emission computed tomography (SPECT) in dementia were evaluated in elderly patients with a mean age of 84 years suffering from dementia (n = 59) and compared to an age- and sex-matched control group with normal cognitive function (n = 14). The demented patients were classified as suffering from primary degenerative dementia (PDD, n = 51) based on DSM-III-R criteria. Moreover, PDD patients were divided into three subgroups of severity of cognitive impairment, according to their Folstein score. Multi-infarct dementia (MID, n = 8) was diagnosed based on clinical features, computed tomographic findings and Hachinski ischaemic score. Images were assessed qualitatively by visual interpretation of shades of colour in cortical regions. A SPECT defect confined to the frontal, parietal, temporal or (parieto) occipital lobe was defined as one lesion. The mean number of SPECT lesions was 1.4 (range 0-4) in the control group, 2.4 (range 0-8) in the PDD group and 2.9 (range 2-5) in the MID group and showed a significant difference (P < 0.02) between groups. To obtain an acceptable level of specificity of 64.3%, a cut-off value of three lesions had to be chosen. In the PDD group, sensitivity was then 25% for the mildly, 43.8% for the moderately and 46.7% for the severely affected PDD subgroup. In the MID group sensitivity was then 75%. Interestingly, in this elderly patient population the location of lesions was homogenously distributed in all groups, including the control group.

Technetium-99m HMPAO SPET in acute supratentorial ischaemic infarction, expressing deficits as millilitre of zero perfusion.

A comparative interim analysis was performed of clinical parameters, computed tomographic (CT) scan results and technetium-99m hexamethylpropylene amine oxime single-photon emission tomography (SPET) findings obtained within 12 h of acute supratentorial ischaemic infarction. First, the applicability for SPET semiquantification in this study of the “method of Mountz”, simultaneously accounting for extent and degrees of hypoperfusion by expressing deficits as millilitre of zero perfusion, was considered. Next, the relative contributions of perfusion SPET and CT scan in the acute stage of ischaemic infarction were compared in 27 patients (mean age 68.8 years). Finally, the correlation of SPET lesions with clinical parameters at onset was evaluated. The method of Mountz represents a workable, accurate virtual parameter, with the assumption that the contralateral brain region remains uninvolved. Interobserver reproducibility in 12 SPET studies, with lesions varying between 6 and 369 cc, showed a correlation coefficentr of 0.99. In practice, because of inconstant distribution of activities in the brain, the method can only be applied slice by slice and not on the total global volume. While the mean delay since the onset of symptomatology was approximately 7 h for both SPET and CT scan, SPET showed lesions concordant with the clinical neurological findings in 100% and CT scan in only 48%. One could hypothesize that SPET examinations performed later would show larger functional defects, because of the development of additional functional changes secondary to biochemical alterations. However, in this regard no statistically significant differences were found between two subproups, taking the median of delay before SPET examination as cut-off. Finally, when comparing the volumes of SPET lesions during the acute stage with clinical parameters, a statistically significant correlation (P<0.01) was found with the Orgogozo Scale scores describing the neurological deficit, but not with the Glasgow Coma Scale or Frenchay Aphasia Screening Test scores obtained on admittance.

Parameters influencing SPET regional brain uptake of technetium-99m hexamethylpropylene amine oxime measured by calibrated point sources as an external standard

Using calibrated point sources as an external standard to convert single-photon emission tomography (SPET) brain counts into absolute values of regional brain uptake (rBU) of technetium-99m hexamethylpropylene amine oxime (HMPAO), the relative contribution of different parameters to interindividual variability of cerebellar rBU was examined in 33 healthy volunteers. Stepwise regression analysis identified body surface as the most important factor underlying interindividual variability (P<0.001), when compared with brain volume. In the normal volunteer population presented, age decrement of rBU corrected for body surface and brain volume equalled 60.5–0.20×age. Based on the data of eight normal volunteers, including four test-retest studies with heart rate (HR) differences greater than 5 units and four test-stress studies with doubling of heart rate after bicycle exercise, influence of heart rate may be expressed by the equation ΔrBU=0.35 ΔHR. Clinically, estimation of the relative influence of different factors allows normalization and extension of the applicability of the rBU quantification method used from longitudinal studies to group comparisons. Interestingly, results of the Daily Stress Inventory Scale and a subjective rating scale suggest the absence of a significant influence of minor stress on rBU. When using one vial per patient, chromatography may be omitted in clinical routine practice and lipophilicity may be estimated as 90% of the injected dose, if administered within 10 min after preparation. Finally, sensitivity of the quantification method was tested in eight volunteers using acetazolamide brain activation and showed a mean increase in cerebellar rBU of 30.2%, varying between 14.1% and 75.9%.

Single photon emission computed tomography using perfusion tracers in seizure disorders

Single photon emission computed tomography (SPECT) using perfusion tracers makes it possible to estimate regional cerebral blood flow (rCBF) and, indirectly, local brain metabolism. It may be possible to detect and follow physiopathological alterations, such as may be seen in seizure disorders. The authors review the principles of and some data on perfusion SPECT in seizure disorders, stress advantages as well as major drawbacks and add their initial experience with Tc-99m hexamethylpropyleneamine oxime (HMPAO) SPECT in febrile convulsions.

Tc-99m HMPAO tomography using a three-headed SPECT system equipped with lead fanbeam collimators

The authors present oblique, coronal, and sagittal tomographic slices of a normal Tc-99m HMPAO study. In addition, some major topographic reference points are given. The images shown demonstrate the high spatial resolution (FWHM 7.3 mm) obtained with a three-headed rotating SPECT system, equipped with lead fanbeam collimators.

High spatial resolution Tc-99m HMPAO brain SPECT in cerebellar embolic infarction

Oblique Tc-99m HMPAO brain SPECT images of a 54-year-old man with brainstem and cerebellar infarcts are presented. Features of particular interest include the high spatial resolution, the embolic nature and the wedge-shaped appearance of the cerebellar infarct, and the presence of reversed cerebral diaschisis without neuropsychologic impairment