Editorial: Dural tail sign

Abstract

In their article in this issue, “A radiopathological classification of dural tail sign of meningiomas,”7 Dr. Fang and his group at Nanfang Hospital in Guangzhou, China, provide a retrospective analysis of 179 patients with convexity meningiomas who underwent surgical treatment. The authors identify 3 goals of the paper: 1) to describe the histopathological features of the tissue found to correlate with the radiographic dural tail sign (DTS), 2) to propose a classification scheme that correlates the histopathology of the DTS with preoperative findings on MRI studies, and 3) to describe the extent of invasion into dura mater based on the different types of DTS. When classifying the DTS into 5 subtypes (smooth, nodular, mixed, symmetrical multipolar, and asymmetrical multipolar) on preoperative 3-T MRI studies, they found significant differences in the incidence of dural invasion, with ascending incidence of invasion from smooth to mixed subtypes. On average, the nodular type was found to have the most extensive dural invasion. Also, statistically significant differences in the representation of WHO Grade I and non–Grade I tumors were found within the subtypes; 33% of meningiomas with a nodular DTS had non–Grade I histopathological features. Meningiomas with the smooth DTS were all found to be Grade I. The most impressive aspect of this paper is the number of patients (179) that the authors were able to include in a relatively short period of time (5 years). All underwent a Simpson Grade I resection, with 3-cm margins from the base of the tumor. Both the short interval of recruitment and standardization of resection limit the variability that could confound analysis of the data, such as surgeon preferences, technological changes in preoperative imaging, and WHO classifications. Another strength of this work is found in the authors’ demonstration that different types of DTS found on preoperative MRI studies may represent unique pathological processes. With this finding, surgeons could theoretically evaluate the DTS of an intracranial lesion presumed to be a meningioma with more scrutiny, because this finding may be more helpful in predicting the extent of dural invasion and likelihood of non–Grade I histopathological findings. The proposed classification is not without its limitations. Although meant to be exhaustive and meticulous regarding all the possible MRI demonstrations of the DTS, there may be room for interpretation about characteristics of the dural tail that represent a mixed versus nodular subtype. Similar difficulty may be encountered when attempting to discriminate the 2 multipolar subtypes. Moreover, the clinical implications of categorizing the DTS into these subtypes are not entirely clear. Although the authors demonstrate that smooth-type DTS is a radiographic sign of Grade I lesions with limited dural invasion, and that nodular-type DTS is a predictor of increased risk of non–Grade I lesions with significant dural invasion, the other subtypes of DTS can occur in non–Grade I lesions, with dural invasion up to 3 cm. Intuitively, the only DTS type that would alter preoperative planning is the smooth type, whereas the other subtypes all demonstrate non–Grade I histopathological features, with significant dural invasion. The results of the radiographic and histopathological evaluations that the authors publish are both unique and significant. However, the surgical conclusions are difficult to justify. The authors recommend a dural resection of at least 2.5 cm from the base of the tumor when possible. Without reporting results of perioperative morbidity, and without long-term follow-up data that demonstrate a significant decrease in risk of recurrence, this would influence current practice, with its historically low morbidity and mortality,6,8 to a new surgical practice that has unknown clinical benefit or consequence. Since Dr. Simpson’s landmark paper in 1957, neurosurgeons have attempted to find factors influencing recurrence of these routinely benign lesions,1–3,5 and “extent of resection” continues to be one of the most significant factors. It is only natural for surgeons to take this knowledge and maximize the proven benefit of this variable. This is not entirely novel, as others have published surgical techniques with the intention of decreasing risk of recurrence, such as the en bloc and Simpson Grade 0 resections.2–4 Qi et al. have provided a very eloquent exposition of the many presentations of the DTS and the potential histopathological significance of these subtypes. However, without knowing the clinical impact on these patients, it is difficult to say whether this should alter practice. (http://thejns.org/doi/abs/10.3171/2012.2.JNS12266)