PMC8769480_01
Preoperative MRI revealed a mass at the right cerebellopontine angle with hypointense on T1WI, hyperintense on T2WI, non-enhanced on contrast-enhanced (CE-) T1WI using gadolinium, and low-dense on CT. The lesion was hyperintense on DWI, and so we diagnosed an epidermoid cyst. BPAS and CISS images revealed the prolonged and distorted trigeminal nerve and the hypointense tumor compared to the CSF. CISS image suggested that the tumor would wholly surround the trigeminal nerve, reach into the Meckel cavity, and offend and compress the REZ of the trigeminal nerve (red circle in A). The postoperative images on day (POD) 3 revealed the loose trigeminal nerve. However, the BPAS, CISS images, and DWI did not show the removed part of the tumor, and the images were almost similar to the preoperative ones (B). Those radiological findings on day 39 still seemed unchanged (C). BPAS: basi-parallel anatomical scanning, CISS: constructive interference in steady state, CSF: cerebrospinal fluid, DWI: diffusion-weighted image, REZ: root entry zone, T1WI: T1-weighted image, T2WI: T2-weighted image.
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F1
CISS images revealed the prolonged and distorted trigeminal nerve and the hypointense tumor compared to the CSF. CISS image suggested that the tumor would wholly surround the trigeminal nerve, reach into the Meckel cavity, and offend and compress the REZ of the trigeminal nerve (red circle in Fig. 1A). However, the BPAS, CISS images, and DWI did not show the removed part of the tumor, and the images were almost similar to the preoperative ones (Fig. 1B). Those radiological findings on day 39 seemed similar (Fig. 1C).
Intraoperative findings: contrary to our expectation based on the preoperative CISS image, the trigeminal nerve (CN V) was not surrounded by the tumor (A). Neuroendoscope revealed that the petrosal vein did not hit the CN V. It also revealed that the tumor compressed the REZ (B), but the tumor was not present in the Meckel cavity (C). Gently retracting the cerebellum, we removed the tumor and its capsule around the trigeminal nerve, avoiding spreading the contents (D). We confirmed that there was no tumor around the REZ (E). We transposed the petrosal vein after tumor removal, which had not hit the trigeminal nerve before tumor removal (F). CISS: constructive interference in steady state, REZ: root entry zone.
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F2
Contrary to our expectation based on the preoperative CISS image, the trigeminal nerve was not surrounded by the tumor (Fig. 2A). Neuroendoscope revealed that the REZ was compressed by the tumor (Fig. 2B), but the tumor was not present in the Meckel cavity (Fig. 2C). Gently retracting the cerebellum, we removed the tumor and its capsule around the trigeminal nerve, avoiding spreading the contents (Fig. 2D). We confirmed that there was no tumor around the REZ (Fig. 2E), and the tumor removal rate was estimated as 30%. We transposed the petrosal vein after tumor removal (Fig. 2F), which had not hit the trigeminal nerve before tumor removal (Figs. 2A, 2B, 2D, and 2E).