Contrast-enhanced fast MRI in differentiating brain toxoplasmosis and lymphoma in AIDS patients

Neuroimaging in Central Nervous System Lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare aggressive high-grade type of extranodal lymphoma. PCNSL can have a variable imaging appearance and can mimic other brain disorders such as encephalitis, demyelination, and stroke. In addition to PCNSL, the CNS can be secondarily involved by systemic lymphoma. Computed tomography and conventional MRI are the initial imaging modalities to evaluate these lesions. Recently, however, advanced MRI techniques are more often used in an effort to narrow the differential diagnosis and potentially inform diagnostic and therapeutic decisions.

Diagnostic accuracy of SPECT, PET, and MRS for primary central nervous system lymphoma in HIV patients: A systematic review and meta-analysis

BACKGROUND

We performed a systematic review and meta-analysis to assess the roles of SPECT, PET, and MRS in distinguishing primary central nervous system lymphoma (PCNSL) from other focal brain lesions (FBLs) in human immunodeficiency virus (HIV)-infected patients.

METHODS

PubMed, Scopus, and Medline were systematically searched for eligible studies from 1980 to 2016. Two authors extracted characteristics of patients and their lesions using predefined criteria.

RESULTS

Eighteen studies on SPECT containing 667 patients, 6 studies on PET containing 108 patients, and 3 studies on MRS containing 96 patients were included. SPECT had a pooled sensitivity of 0.92 (95% CI: 0.85-0.96) and specificity of 0.84 (95% CI: 0.74-0.90) in differentiating PCNSL from other FBLs. For the 6 studies that used only pathology and/or serology as the gold standard, the pooled sensitivity was 0.85 (95% CI: 0.72-0.97) and the pooled specificity was 0.73 (95% CI: 0.54-0.92).

CONCLUSION

SPECT has good diagnostic accuracy for discriminating PCNSL from other FBL-causing disorders in HIV patients. However, the actual sensitivity and specificity of SPECT may be lower than expected if only pathology and/or serology was used as the gold standard. PET may be superior but has less supporting clinical data and is more expensive.

Toxoplasma gondii: 25 years and 25 major advances for the field

This article is an attempt to identify the most significant highlights of Toxoplasma research over the last 25 years. It has been a period of enormous progress and the top 25 most significant advances, in the view of this author, are described. These range from the bench to the bedside and represent a tremendous body of work from countless investigators. And, having laid out so much that has been discovered, it is impossible not to also reflect on the challenges that lie ahead. These, too, are briefly discussed. Finally, while every effort has been made to view the field as a whole, the molecular biology background of the author almost certainly will have skewed the relative importance attached to past and future advances. Despite this, it is hoped that the reader will agree with, or at least not disagree too strongly with, most of the choices presented here.

Nocardia brain abscess mimicking high-grade necrotic tumor on perfusion MRI

Differentiating a pyogenic cerebral abscess from a cystic brain tumor can be a challenge when using morphological and functional imaging techniques. Several studies on MRI perfusion-weighted imaging (PWI) have demonstrated that enhancing abscess capsules have lower cerebral blood volume ratios (rCBV) than the enhancing rims of necrotic tumors. We report a 67-year-old male with a Nocardia cerebral abscess showing restricted diffusion in the necrotic center, but high values for rCBV in the enhancing capsule on PWI, therefore mimicking a high-grade necrotic tumor. Differential diagnosis between cerebral abscesses and necrotic tumors is greatly improved by the adjunct of diffusion-weighted imaging (DWI) and PWI to the morphological magnetic resonance findings; yet there is still overlap. That an abscess may show increased rCBV along the capsule, therefore mimicking a hypervascular brain tumor on PWI, should be considered when attempting a radiological diagnosis of a ring-enhancing brain lesion.

Clinical importance of delayed MRI contrast enhancement of primary central nervous system lymphoma in AIDS

Accurately distinguishing between cerebral toxoplasmosis and primary central nervous system lymphoma (PCNSL), still the most common secondary CNS mass lesion complications of AIDS, has long represented a diagnostic challenge in those with HIV. A young adult male with AIDS presented with evolving ophthalmoplegias, Parinaud's syndrome and gait dysfunction. MRI with gadolinium contrast revealed a brainstem lesion failing to enhance on initially obtained post-contrast images yet prominently enhancing on images acquired endmost within the same scanning session. Biopsy ultimately confirmed lesion aetiology as PCNSL. While the definitive diagnosis of PCNSL generally requires brain biopsy, different MRI contrast-enhancement time courses of PCNSL versus toxoplasmosis (PCNSL tends to peak-enhance sooner than toxoplasmosis) can provide differential diagnostic insight. These images underscore the delayed nature of PCNSL contrast enhancement and demonstrate the diagnostic importance of attending to post-gadolinium image acquisition timing to help inform utilisation of MRI for PCNSL identification.

MR and TL-210 spect imaging with pathologic correlation for the assessment of CNS lymphoma vs. toxoplasmosis in AIDS patients

PURPOSE

Analyze the value of TL-201 (Tl) brain single-photon emission computed tomography (SPECT), to differentiate CNS lymphoma from toxoplasmosis in AIDS patients.

MATERIAL AND METHODS

Twenty-four AIDS patients with MR enhancing lesion(s), underwent a brain Tl SPECT. Final diagnosis was established by pathology and clinical/MR follow-up.

RESULTS

Nine patients had CNS tumor, 9 toxoplasmosis and 6 other non-tumorous lesions. The sensitivity of T1 to diagnose CNS tumor was 77% and the specificity 93%. Two false negative studies correspond to tumors with significant necrosis.

CONCLUSIONS

T1 proved useful for differentiating brain neoplasm from toxoplasmosis. Tumors with significant necrosis, did not show the expected increase in T1 uptake. Determination of T1 uptake ratios help detect tumor with faint tracer uptake.

Brain abscess and cystic brain tumor: discrimination with dynamic susceptibility contrast perfusion-weighted MRI

Differentiating between brain abscesses and cystic brain tumors such as high-grade gliomas and metastases is often difficult with conventional MRI. The goal of this study was to evaluate the diagnostic utility of perfusion MRI to differentiate between these pathologies. MRI was performed in 19 patients with rim-enhancing brain lesions (4 pyogenic abscesses, 8 high-grade gliomas, 7 metastases). In addition to standard MR sequences, trace diffusion-weighted MRI with apparent diffusion coefficient (ADC) maps and perfusion-weighted MRI by using a first-pass gadopentetate dimeglumine T2*-weighted gradient echo single-shot echo-planar sequence were performed. Relative cerebral blood volume (rCBV) ratios were obtained via the values of the capsular portions of the lesions and the normal white matter. All the abscesses had markedly hyperintense signals in trace diffusion images, whereas they had significant hypointense signals in ADC images. In perfusion-weighted images, the capsular portions of the abscesses demonstrated low colored areas compared with the normal white matter and the rCBV ratio calculated was 0.76 +/- 0.12 (mean +/- SD). All but two of the cystic tumors showed low signal intensity on trace diffusion-weighted images and high signal intensity on ADC maps. Hyperintense signal was found in two brain tumors mimicking brain abscesses on trace diffusion images. The rCBV values in high-grade gliomas and metastases were 5.51 +/- 2.08 and 4.58 +/- 2.19, respectively. The difference between abscesses and cystic tumors was statistically significant (P = 0.003). Perfusion MRI may allow the differentiation of pyogenic brain abscess from cystic brain tumors, making it a strong additional imaging modality in the early diagnosis of these two entities.

Distinction between cerebral abscesses and high-grade neoplasms by dynamic susceptibility contrast perfusion MRI

OBJECTIVE

The purpose of the study was to determine whether dynamic susceptibility contrast perfusion MRI allowed distinction of cerebral abscesses from cystic high-grade brain neoplasms.

CONCLUSION

In this small preliminary study, dynamic susceptibility perfusion MRI allowed distinction of cerebral abscesses from rim-enhancing high-grade gliomas. Validation of these results using a prospective large study is warranted.

CNS lymphoma in an AIDS patient involving the posterior fornix case report

We report an unusual presentation of CNS lymphoma involving the posterior fornix in a patient with AIDS. The patient's initial symptoms included progressive cognitive impairment, consistent with AIDS dementia, as well as impotence and urinary retention suggestive of myelopathy. An MR scan with gadolinium-DTPA enhancement demonstrated enhancing lesions in the cerebellum and in the posterior fornix. At autopsy, the later lesions proved to be lymphoma. This case demonstrates the unusual clinical features that may occur with lesions in the limbic system and importance of gadolinium-enhanced MRI in the evaluation of symptoms of cognitive impairment in patients with advanced HIV infection.