N-Acetyl peak in MR spectra of intracranial metastatic mucinous adenocarcinomas

Peak Resembling N-acetylaspartate (NAA) on Magnetic Resonance Spectroscopy of Brain Metastases

Background and Objectives: Differentiating between a high-grade glioma (HGG) and solitary cerebral metastasis presents a challenge when using standard magnetic resonance imaging (MRI) alone. Magnetic resonance spectroscopy (MRS), an advanced MRI technique, may assist in resolving this diagnostic dilemma. N-acetylaspartate (NAA), an amino acid found uniquely in the central nervous system and in high concentrations in neurons, typically suggests HGG over metastatic lesions in spectra from ring-enhancing lesions. This study investigates exceptions to this norm. Materials and Methods: We conducted an MRS study on 49 histologically confirmed and previously untreated patients with brain metastases, employing single-voxel (SVS) techniques with short and long echo times, as well as magnetic resonance spectroscopic imaging (MRSI). Results: In our cohort, 44 out of 49 (90%) patients demonstrated a typical MR spectroscopic profile consistent with secondary deposits: a Cho peak, very low or absent Cr, absence of NAA, and the presence of lipids. A peak at approximately 2 ppm, termed the "NAA-like peak", was present in spectra obtained with both short and long echo times. Among the MRS data from 49 individuals, we observed a peak at 2.0 ppm in five brain metastases from mucinous carcinoma of the breast, mucinous non-small-cell lung adenocarcinoma, two metastatic melanomas, and one metastatic non-small-cell lung cancer. Pathohistological verification of mucin in two of these five cases suggested this peak likely represents N-acetyl glycoproteins, indicative of mucin expression in cancer cells. Conclusions: The identification of a prominent peak at 2.0 ppm could be a valuable diagnostic marker for distinguishing single ring-enhancing lesions, potentially associated with mucin-expressing metastases, offering a new avenue for diagnostic specificity in challenging cases.

Clinical value of N-acetyl mucinous compounds and lipid peaks in differentiating benign and malignant ovarian mucinous tumors by MR spectroscopy

PURPOSE

To retrospectively evaluate the clinical significance of the peaks of N-acetyl mucinous compounds (NAMC) at 2 ppm and lipid at 1.3 ppm in in-vivo proton magnetic resonance (MR) spectroscopy for distinguishing benign and malignant mucinous tumors in patients with ovarian masses.

METHODS

MR spectroscopy was performed in patients with pathologically diagnosed mucinous ovarian tumors at 3 T MRI system. The peaks of NAMC, lipid, and total choline compounds (tCho) were classified into three classes in comparison with the noise level by visual estimation. The NAMC concentration was quantified relative to unsuppressed water by using LCModel analysis.

RESULTS

A total of 27 ovarian mucinous tumors in 27 patients were included in this study. The NAMC peak was observed in all 27 mucinous tumors, and the lipid peak was observed in 14 of 27 tumors: 1 of 9 benign tumors (11%), and 13 of 18 malignant tumors (11 borderline malignancies and 7 carcinomas) (72%). The presence of the lipid peak for the diagnosis of malignant mucinous tumor showed generally better diagnostic ability than MR imaging, with a sensitivity of 72%, specificity of 89%, accuracy of 78%, PPV of 93%, and NPV of 62%. The concentration of the NAMC in malignant mucinous tumors tended to be higher than that in benign mucinous tumors, but there was no statistically significant difference.

CONCLUSIONS

The bimodal peaks of NAMC and lipid are suggestive of malignant mucinous tumors, and the presence of the lipid peak may be useful in distinguishing benign from malignant ovarian mucinous tumors.

Role of MR spectroscopy in diagnosis of intracranial neuroenteric cyst

INTRODUCTION

Neuroenteric cysts are rare benign endodermal lesions of the central nervous system that result from incomplete resorption of neuroenteric canal and mostly found in cervical and upper thoracic spinal canal. Intracranial neuroenteric cysts are extra axial and commonly located anteriorly in the posterior cranial fossa. MRI demonstrates variable intensity within the lesion on T1, T2W, and DWI sequences.

METHODS

Three cases of posterior fossa non-enhancing cystic lesions of variable signal intensity underwent MRI with MR spectroscopy, where MR spectroscopy demonstrated dominant peak at 2 ppm, mimicking normal Nacetyl aspartate (NAA).

CONCLUSION

MR spectroscopy in addition to conventional MRI may help in differentiating intracranial neuroenteric cyst from its close differentials.

MRS of pilocytic astrocytoma: The peak at 2 ppm may not be NAA

PURPOSE

To determine whether the chemical shift of residual N-acetylaspartate (NAA) signal in pilocytic astrocytomas (PA) is consistent with the position of the NAA peak in controls.

METHODS

MR spectra from 27 pediatric World Health Organization (WHO) grade I pilocytic astrocytoma patients, fifteen patients with WHO grade II and high-grade (III-IV) astrocytomas, and 36 controls were analyzed. All spectra were acquired with a short echo time (35 ms), single voxel point-resolved spectroscopy sequence on clinical 3 tesla scanners. Fully automated LCModel software was used for processing, which included the fitting of peak positions for NAA and creatine (Cr).

RESULTS

The chemical shift difference between the NAA and Cr peaks was significantly smaller (by 0.016 ± 0.005 parts per million, P < 1e-10) in PAs than in controls and was also smaller than what was observed in infiltrative astrocytomas.

CONCLUSION

The chemical shift position of the residual NAA peak in PAs is not consistent with NAA. The signal likely originates from an N-acetyl group of one or more other chemicals such as N-acetylated sugars. Magn Reson Med 78:452-456, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Delayed post-traumatic fronto-ethmoidal sinus mucocele evaluated with short and long TE MR spectroscopy

Mucoceles are slow-growing, benign, expansile, mucoid-filled masses developing after obstruction of the sinus ostium. Late post-traumatic mucoceles are relatively rare entities and the literature is limited to single case reports. We describe an unusual case of post-traumatic fronto-ethmoidal mucocele, evaluated with computed tomography (CT), magnetic resonance imaging (MRI) and proton MR-spectroscopy ((1)H-MRS). As a contribution to the diagnostic work-up of the mucocele, (1)H-MRS demonstrates a dominant peak at 2.0 ppm at long echo time (TE) and an additional component at 3.8 ppm at short TE due to mucus glycoprotein compounds of the mucocele.

Advanced magnetic resonance imaging biomarkers of cerebral metastases

There are a number of magnetic resonance imaging techniques available for use in the diagnosis and management of patients with cerebral metastases. This article reviews these techniques, in particular, the advanced imaging methodologies from which quantitative parameters can be derived, the role of these imaging biomarkers have in distinguishing metastases from primary central nervous system tumours and tumour mimics, and metrics that may be of value in predicting the origin of the primary tumour.

The relationship between Cho/NAA and glioma metabolism: implementation for margin delineation of cerebral gliomas

Background

The marginal delineation of gliomas cannot be defined by conventional imaging due to their infiltrative growth pattern. Here we investigate the relationship between changes in glioma metabolism by proton magnetic resonance spectroscopic imaging (¹H-MRSI) and histopathological findings in order to determine an optimal threshold value of choline/N-acetyl-aspartate (Cho/NAA) that can be used to define the extent of glioma spread.

Method

Eighteen patients with different grades of glioma were examined using ¹H-MRSI. Needle biopsies were performed under the guidance of neuronavigation prior to craniotomy. Intraoperative magnetic resonance imaging (MRI) was performed to evaluate the accuracy of sampling. Haematoxylin and eosin, and immunohistochemical staining with IDH1, MIB-1, p53, CD34 and glial fibrillary acidic protein (GFAP) antibodies were performed on all samples. Logistic regression analysis was used to determine the relationship between Cho/NAA and MIB-1, p53, CD34, and the degree of tumour infiltration. The clinical threshold ratio distinguishing tumour tissue in high-grade (grades III and IV) glioma (HGG) and low-grade (grade II) glioma (LGG) was calculated.

Results

In HGG, higher Cho/NAA ratios were associated with a greater probability of higher MIB-1 counts, stronger CD34 expression, and tumour infiltration. Ratio threshold values of 0.5, 1.0, 1.5 and 2.0 appeared to predict the specimens containing the tumour with respective probabilities of 0.38, 0.60, 0.79, 0.90 in HGG and 0.16, 0.39, 0.67, 0.87 in LGG.

Conclusions

HGG and LGG exhibit different spectroscopic patterns. Using ¹H-MRSI to guide the extent of resection has the potential to improve the clinical outcome of glioma surgery.