Diagnosing necrotic meningioma: a distinctive imaging pattern in diffusion MRI and MR spectroscopy

Abstract

The differential diagnosis of necrotic meningiomas includes brain abscess and malignant neoplasms. We report and discuss hereby the work-up of two patients diagnosed with necrotic meningioma using diffusion-weighted imaging, magnetic resonance spectroscopy, resective surgery, and histopathology. The purpose of the present article is to add to the scant literature on the use of advanced imaging modalities in the routine investigation of brain lesions and their utility in arriving at the final diagnosis.

Introduction

Meningiomas are the most common primary central nervous system (CNS) tumors, accounting for more than one third of all primary brain and spinal neoplasms.¹ The incidence of meningioma increases with age with a median age at diagnosis of 65 years and overall rise in the number of affected patients as populations age.² Most meningiomas are benign and have a typical imaging appearance of unilobar extra-axial mass, sharply demarcated with homogeneous contrast enhancement. However, approximately 15% of meningiomas may demonstrate atypical imaging features including heterogeneous or rim enhancement, cyst formation or intramural hemorrhage.³ Atypical radiological appearance may result in misinterpretation and late diagnosis. A definitive diagnosis and classification of meningioma as benign, atypical, or malignant lesion requires a pathologic confirmation. Nevertheless, when obtaining tissue is difficult or poses a risk for further neurologic deficits, computed tomography (CT) or magnetic resonance imaging (MRI) may be sufficient for clinical decision making. However, conventional imaging studies may be inadequate for differentiating necrotic-neoplastic lesions from inflammatory lesions with a necrotic core. Previous studies suggested MR spectroscopy (MRS) and diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps as complementary modalities for distinction between these entities. MRS, providing a signature metabolic profile of the lesion, has been used to demonstrate characteristic amino acids resonance peaks in necrotic brain tumors.⁴ DWI was used to illustrate the absence of diffusion restriction in necrotic tumors, contrary to the reduced diffusion seen in brain abscess with purulent fluid.⁴

Two cases with atypical, centrally necrotic meningioma are presented, with their unique MRS and DWI studies and histopathological findings confirming necrotic meningioma. This article seeks to add to the scant literature on the optimal imaging modalities for identification of necrotic meningioma.

Patient 1

A 54-year-old previously healthy woman presented to the emergency department with sudden-onset headache and seizures. Her initial investigation included a contrast-enhanced CT scan demonstrating a hypodense lesion in the right parietal cortex with rim enhancement and perilesional edema. Subsequent MRI scans revealed a rounded, dural-based, non-homogeneous lesion with minor surrounding edema (Figure 1(a), (b) and (c)). Coronal T1-weighted gadolinium-enhanced MRI showed rim enhancement with dural thickening (“dural tail” sign) (Figure 1(d)). Axial T2-weighted MRI revealed small calcifications (Figure 1(e)) and DWI showed enhanced diffusion in the center of the lesion with restricted diffusion in the periphery (Figure 1(f)).

Figure 1.

MRI demonstrating sagittal T1-weighted (a), axial T2-weighted (b), and axial FLAIR (c) images with a round non-homogenous mass and minor surrounding brain edema; coronal T1 image after Gd-DTPA (d) showing rim like enhancement with dural attachment and dural thickening (“dural tail” sign); axial T2 -weighted fast field echo image (e) showing small calcifications; DWI (f) showing restricted diffusion.

Single voxel MRS of the lesion, including the tumor wall, showed broad multiple signals between 2 ppm and 2.4 ppm and at 3.8 ppm from glutamate (Glu) and glutamine (Glx), respectively, characteristic for meningiomas (Figure 2(a)). MRS of the center of the lesion confirmed prominent resonance peaks of lactate doublet (1.3 ppm) and choline (Cho, 3.2 ppm), without characteristic peaks for abscesses (Figure 2(b)). A following resective surgery and a histopathological examination revealed meningioma with regions of coagulation-type necrosis (Figure 3).

Figure 2.

Single voxel ¹H-MRS. (a) Whole lesion MRS including tumor wall. Note the broad multiple signals between 2 and 2.4 and at 3.8 ppm from glutamate (Glu) and glutamine (Glx), respectively, characteristic for meningiomas. (b) MRS of the center of the mass shows prominent lactate (Lac) doublet around 1.3 ppm and a choline peak (Cho). Characteristic peaks for abscesses (succinate (2.4 ppm), acetate (1.9 ppm), valine (0.9 ppm), and leucine (3.6 ppm) are absent.

Figure 3.

Pathological confirmation of necrotic meningioma: hematoxylin and eosin staining, magnification ×200. Viable tissue is present on the right. Few psammoma bodies can be seen. Most of the tissue shows coagulation-type necrosis and cellular shadows (left). Note the gradual decomposition of the tissue from right (rim) to left (core).

Patient 2

A 53-years-old man was admitted to the neurosurgical department for a planned removal of a brain tumor diagnosed as oligodendroglioma. The pre-surgical MR investigation revealed an additional extracranial mass located in the tentorial incisura, with homogeneous contrast enhancement and restricted diffusion suggesting meningioma (Figure 4(a)) and no surgical intervention was required. In a follow-up MRI scan, 2 years later, peripheral, rather than a central lesion enhancement was demonstrated (Figure 4(b)) with facilitated diffusion and subsequent gliosis and meningioma shrinkage (Figure 4(c)).

Figure 4.

MRI demonstrating meningioma at the apex of the tentorial incisura: (a) coronal T1-weighted image after Gd-DTPA with homogeneous enhancement; (b) coronal T1-weighted image after Gd-DTPA following resection of the right-sided oligodendroglioma showing loss of central enhancement due to spontaneous central necrosis; (c) axial FLAIR image with post-operative gliosis and meningioma shrinkage after an oligodendroglioma resection.

MRS of the center of the lesion illustrated resonance peaks of lactate (1.3 ppm) and choline (3.2 ppm) (Figure 5). Due to a localized pressure on the nearby sinuses, the lesion was surgically removed. Both the surgical and pathological reports confirmed the diagnosis of meningioma with poor vascularity and hemosiderin deposition, all features consistent with necrosis.

Figure 5.

Single voxel ¹H-MRS of the center of the mass shows resonance peaks of lactate (1.3 ppm) and choline (3.2 ppm).

Discussion

Most meningiomas can be diagnosed by conventional MRI. Nevertheless, a meningioma with atypical appearance may mimic brain abscess, metastases, or other tumor types. The clinical presentation and initial imaging findings for “patient 1” could suggest an acute CNS infection with abscess formation and raised a clinical dilemma. Standard CT and MRI studies were not sufficient to establish the diagnosis, but MRS metabolic profiling and DWI with ADC maps provided useful additional information to help differentiate between necrotic tumor and brain abscess (Table 1). A judicious interpretation of ADC should take into account the pathomechanism of necrosis development within a tumor. Necrotic tissue demonstrates a pattern of transition from restricted to enhanced diffusion as the tissue decomposes. This alteration therefore, can be optimally demonstrated in the DWI and ADC modalities. While restricted diffusion pattern is characteristic for abscesses, necrotic tumor should remain a differential diagnosis in a non-enhancing lesion. Based on our first observation, when a second patient presented at our center with a late finding of a non-enhancing lesion (“patient 2”), an MRS and DWI investigation were carried out. In keeping with the metabolic and diffusion pattern seen in “patient 1,” necrotic meningioma was highly suspected and a definitive diagnosis was confirmed in a subsequent tumor resection. In conclusion, in both cases, ancillary imaging modalities were employed and proved to be helpful in arriving at the final diagnosis. MRS and DWI studies are therefore suggested as emerging modalities to diagnose and monitor the progression of atypical meningiomas.

Table 1.

Comparison of the characteristics of necrotic meningiomas (early and late phases) and brain abscess using different MRI sequences.

MRI sequences	Brain abscess	Necrotic meningioma
		Early phase	Late phase (cystic)
DWI	Hyperintense	Hyperintense	Hypointense
ADC	Hypointense	Hypointense	Hyperintense
MRS (resonance peaks)	Lactate, acetate, and amino acids	Glutamine, glutamate, choline	Lactate
T1 with gadolinium	Ring enhancement lesion	Heterogeneous enhancement	Ring enhancement lesion

ADC: apparent diffusion coefficient; DWI: diffusion-weighted imaging; MRS: magnetic resonance spectroscopy.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.