MVNT is an unusual, neuronal lesion which was initially described by Huse et al. in 2013 and was later included in the 2016 updated WHO classification of tumors of the CNS [1]. The true epidemiology of these tumors is unknown. Before the introduction of this entity, it is highly likely that these lesions were underrecognized.
Conventional MRI is the primary imaging modality for the diagnosis of MVNT. MVNTs exhibit a characteristic appearance on MRI imaging. Only the imaging feature may be sufficient in the diagnosis. All lesions in our study contain nodules following the gyral contour and these nodules are hyperintense on T2 and T2/FLAIR sequences. They do not enhance and cause mass effect. Diffusion restriction and peripheral edema were absent in all cases. Nonsuppression pattern on FLAIR indicated high protein or solid component within vacuoles [3]. These MRI findings are in accordance with the cases in the radiology literature.
Because of its pathognomonic imaging appearance and asymptomatic nature, it was called a ‘leave-me-alone’ brain lesion by Nunes et al. [3]. Although seizures were expressed as the most common clinical finding by Huse et al. [1], in our study seizure was observed in only one patient. Headache was by far the most common complaint and was seen in seven of 11 patients. Nunes et al. also reported that headache (16/33) and seizure (8/33) were most common clinical findings. Similarly, in the Buffa et al. study seizure or equivalents (5/16), and non-focal headache (5/16), were the most commonly seen complaints [2, 3]. MVNTs are mostly incidental findings on MR imaging studies.
One case in our cohort was a 16-year-old female patient who had a temporary numbness on both hands mostly left. On MR imaging right parietooccipital lesion was demonstrated. No changes in follow-up imaging was observed after 6 months. The patient’s symptoms disappeared at follow-up. Alizada et al. reported that a similar patient, who was a 17-year-old female, had numbness and MRI showed the lesion was hyperintense on T2-WI and FLAIR sequences without any contrast enhancement. After surgery, the lesion was diagnosed as MVNT histologically [4].
Alsufayan et al. reported that %20 of MVNT had cystic areas [5], and in our study similar MRI finding was shown in only one case (%9). Our two patients (%18) had cortical and subcortical white matter involvement on imaging which was described before by Alsufayan %57 of patients (17/30) and Lecler %7.8 of patients (5/64) [5, 6]. The white matter hyperintensity on T2/FLAIR adjacent to the bubble-like lesions was found in four of our cases (%36). This finding was reported by Nunes et al. at similar rate (%45) [3].
Based on the literature, we observed that CT was not recommended in the diagnosis or follow-up in these patient groups, and Yamaguchi et al. [7] reported that CT scans showed no abnormality. Nagaishi et al. [8] described CT findings as low-density lesions without calcification or cysts. In our retrospective study, lesion which was described in MRI scan could not be identified on the CT images of 5 patients (%83). One patient (%9) had a cystic area which could be recognized as a hypodense lesion on CT.
In our study, five lesions (%45) were located in the parietal lobe and 3 lesions (%27) affected more than 1 lobe (parietooccipital). When it was first described by Huse et al., 7 of 10 cases were confined to the temporal lobes [1]. Lecler et al. [6] reported that the MVNTs were mostly located in the frontal (20/64) and parietal lobe (26/64). The location of this entity seems to be non-discriminatory.
Surgery can be performed on symptomatic patients. In the literature, the symptoms have mostly regressed following resection without regrowth [1, 9]. None of our patients were undergone surgery, since the exact relationship between symptoms and lesions was not established.
The differential diagnosis of this lesion should include dysembryoplastic neuroepithelial tumor (DNET), enlarged periventricular space (PVS) and focal cortical dysplasia. The absence of enhancement, cortical involvement, mass effect and the presence of clustered appearance help to distinguish MVNT from DNET. In addition, DNET has a bright rim sign on FLAIR sequences and may scallop the inner table of the skull. Hyperintensity on FLAIR excludes the possibility of enlarged perivascular space. Focal cortical dysplasia is characterized by focal cortical thickening and blurring of white–gray matter junction. Some MVNTs may show a T2 FLAIR hyperintense radial like band as in focal cortical hyperplasia (transmantle sign), but the presence of cortical and gray-white matter junction involvement is consistent with focal cortical dysplasia [5].
However, there were some limitations to our study (shortness of mean follow-up duration, absence of histologic proof and MR spectroscopy images and variety of MRI devices used from different models), MVNT seems to be a static lesion, and no progression was detected in our study. According to our experience and point of view, follow-up with MRI is sufficient in the management of patients.
