MRI findings for the pretreatment diagnosis of small Meckel's cave tumors: comparison of meningiomas and schwannomas.

Abstract

Background: Both meningiomas and schwannomas are the most common Meckel's cave (MC) tumors in terms of distinct imaging features. When they are small, they may present with similar imaging characteristics that make their diagnosis difficult. The aim of this study was to diagnose small meningiomas and schwannomas of the MC on the basis of their clinical and MRI findings.

Methods: The clinical data of 33 patients who were diagnosed with small MC tumors (SMCTs) (17 schwannomas, 16 meningiomas) between August 2002 and August 2023 were retrospectively evaluated. SMCTs were defined as MC tumors that were less than 3 cm in size. We analyzed their clinical and MRI findings, including demographic features, lesion morphologies and changes in adjacent structures.

Results: The rate of subtotal resection of meningiomas less than 3 cm in size was significantly lower than that of schwannomas less than 3 cm in size (43.8% vs. 100%, p = 0.032). The MRI features of meningiomas and schwannomas were as follows: 1) a prominent dura tail sign (8/16 [50%] vs. 0/17 [0%], p < 0.001); 2) few cystic components (0/16 [0%] vs. 9/17 [52.94%], p < 0.001); 3) lower minimum ADC (ADCmin) values (820.575 ± 302.545 [86.1-1144.4] vs. 1372.424 ± 561.337 [355.7-2616.6], p < 0.001); and 4) minimal ipsilateral masticatory muscle atrophy (-6.71% ± 22.43% [-85.71% ~ 13.79%] vs. 11.24% ± 11.98% [-14% ~ 38%], p < 0.001). Very small MC tumors (VSMCTs) were ≤ 2 cm in size, and the subgroup analysis of very small meningiomas and schwannomas revealed no differences in terms of ipsilateral masticatory muscle atrophy (p = 0.078), prominence of the dural tail (p = 0.236), or the presence of cystic components (p = 0. 364). However, the ADCmin values were significantly lower for very small meningiomas than for very small schwannomas (p = 0.009).

Conclusion: MRI features such as a prominent dural tail appearance, the presence of fewer cystic components, and less masticatory muscle atrophy may aid in differentiating meningiomas from schwannomas less than 3 cm in size. The ADC and DWI parameters provided additional critical insights, particularly for VSMCTs, thus facilitating preoperative diagnoses.