Perfusion MRI may facilitate the diagnosis of a tumefactive demyelinating lesion
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.263196
Source of Support: None, Conflict of Interest: None
Tumefactive demyelinations are rare demyelinating lesions >2 cm in size, usually single, and resemble a tumoral lesion (high-grade glioma) on imaging as well as on histopathology. Certain conventional magnetic resonance imaging (MRI) features, including a relative lack of mass effect, less substantial perifocal edema, vessel traversing through the lesion, and an open ring enhancement may suggest the diagnosis of tumefactive demyelinating lesions (TDL) with a high degree of certainty. However, these findings are non-specific and these lesions possess both radiological and pathological diagnostic problems, often leading to wrong therapeutic decisions. A TDL misdiagnosed as a neoplasm could lead to an unnecessary surgical intervention or even radiation therapy, which could exacerbate the demyelinating disease.
A 22-year old lady presented with weakness and tingling of left side of her body and headache, for 1 week. The headache was holocranial and continuous in nature and associated with projectile vomiting. She also had fever and myalgia 2 weeks prior to this episode. She had a past history of acute transverse myelitis with paraparesis 6 months back that improved with steroids. She did not receive any disease-modifying drugs administered in multiple sclerosis. No sensory loss or cerebellar signs were present.
The evoked potential study was normal in both eyes. The antinuclear antibody (Ab) was negative. The anti-phospholipid Ab profile revealed the anti-beta-2 glycoprotein 1 (GP1) <3.0 AU/ml, anti-cardiolipin antibody (ACLA IgG)-3.3 GP1/ml, and IgM-5.3 mpl/ml. The anti-double stranded-DNA titres were <10.0 IU/ml. The cerebrospinal fluid (CSF) glucose was 94 mg/dl and proteins were 32 mg/dl. The cryptococcal antigen agglutination test was negative. No pus cells or red blod cells were seen. The CSF was also negative on bacterial culture.
The cranial magnetic resonance imaging (MRI) showed a T2 and fluid attenuated inversion recovery (FLAIR) hyperintense lesion in the right frontal lobe with moderate surrounding edema. The peripheral rim was showing diffusion restriction on diffusion-weighted imaging (DWI). The lesion was hypointense on T1WI and showing an intense rim enhancement on post-contrast T1W sequence. The enhancing rim was relatively thinner and deficient towards the cortex. The arterial spin labeling (ASL) sequence showed reduced cerebral blood flow (CBF) in the enhancing region as compared to the normal appearing contralateral brain parenchyma [Figure 1]. An imaging diagnosis of tumefactive demyelinating lesion (TDL) was kept based on the conventional MRI findings and the low perfusion parameters. The patient was treated with intravenous methylprednisolone (1,000 mg/day) for 3 days, followed by high-dose oral prednisolone (1 mg/kg/day) that was tapered over 1 month. Her left hemiparesis gradually improved. The follow-up MRI done after 3 months showed significant resolution of the lesion with minimal residual gliosis without any enhancement or mass effect [Figure 2].
TDL are rare demyelinating lesions >2 cm in size and mimic a tumoral lesion on imaging. These belong to a sub-group of demyelinating lesions with atypical clinical presentations and imaging findings and may mimic an intracranial neoplasm (a high-grade glioma or a lymphoma).
Tumefactive demyelinations are more common in children with a female predominance. Clinically, TDLs present with focal neurological deficits and/or seizures, often associated with symptoms of intracranial hypertension.
On MRI, these lesions are solitary, usually >2 cm in size associated with mass effect, perifocal edema, and incomplete ring enhancement. Their detailed clinical and imaging findings and their limitations have been described in [Table 1].
The characteristic imaging findings of TDL were seen in the present case. Hypoperfusion was seen on ASL within the center as well as in the enhancing rim. The ASL sequence of MRI measures the cerebral blood flow (CBF) by magnetically labeling arterial water and using it as an endogenous tracer. The entire lesion had a low value of CBF as compared to the contralateral normal appearing brain parenchyma.
The differential diagnosis of tumefactive demyelination includes neoplasms such as a high-grade glioma and metastasis, and infections such as an abscess. Abscesses usually have central diffusion restriction. Glioma and metastasis have disproportionate edema, although this finding is non-specific. Multiple lesions in the periventricular white matter, corpus callosum, brachium pontis, or in the dorsolateral column of spinal cord in an appropriate clinical setting supports the diagnosis of demyelination. Optic neuritis, if present, also favors demyelination rather than a tumor. Gliomas show irregular rim enhancement and have a high CBF and cerebral blood volume (CBV) within the enhancing portion of the lesion as well as perilesional edema, due to tumor infiltration in the white matter.
Imaging findings that favor a TDL include the presence of a alrge lesion with relatively less surrounding edema and mass effect. Incomplete ring enhancement, if present, is highly suggestive of TDL. The enhancing ring remains open towards the cortex. The enhancing portion of the ring is believed to represent the leading edge of demyelination and thus points to the white matter side of the lesion. The central non-enhancing core represents a more chronic phase of the inflammatory process. Dilated veins traversing through the lesion may be found in tumefactive demyelination. On DWI, the TDLs usually show an increased diffusion with a mild increased apparent diffusion coefficient (ADC) value, although patchy or rim restriction may be seen in larger lesions. This is a useful differentiating tool from cerebral abscesses that show a central diffusion restriction with a low apparent diffusion coefficient (ADC) value. The magnetic resonance spectroscopy (MRS) reveals reduced N-acetylaspartate (NAA) and increased choline peak in TDL.
Perfusion MRI can be used to differentiate TDL from a high-grade glioma. High-grade gliomas are characterized by the presence of neoangiogenesis and vascular endothelial proliferation and show a high regional cerebral blood flow r(CBF) and regional cerebral blood volume r(CBV). TDLs are characterized by intrinsically normal or inflamed vessels, rarely associated with vascular hyperplasia and have a low rCBF and rCBV. Frank neovascularization is absent in TDL.,,
Most TDL are monophasic, show an excellent response to steroids and undergo rapid resolution on follow up in the form of substantial decrease in size and enhancement, as seen in our patient. This characteristic is not seen in patients with a high-grade glioma or lymphoma.
When the lesion is large and solitary, without any white matter abnormality to suggest demyelination, an intracranial neoplasm cannot be ruled out based on the conventional MRI. In such cases, addition of perfusion may help in differentiating a TDL from a high-grade glioma. An accurate diagnosis is necessary to prevent unnecessary interventions in these patients.
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[Figure 1], [Figure 2]