PMC10247221_01
Constructive interference in steady-state magnetic resonance imaging (MRI, A) showing that the right superior cerebellar artery (SCA) compresses the trigeminal nerve (CN-V, arrowhead). Computed tomography (CT, B) showing the enlarged mastoid emissary canal (arrowhead).
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CT angiography (C-F) shows that the right internal jugular vein (IJV) is severely stenosed by the compression of the styloid process and the transverse process of the atlas vertebra (arrowhead). The mastoid emissary vein (MEV) and occipital veins are enlarged.
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Magnetic resonance imaging (MRI) revealed that the offending vessel was the superior cerebellar artery (SCA), which compresses the root of the right trigeminal nerve in the rostral direction (Fig. 1A). Preoperative computed tomography (CT) revealed an enlarged mastoid emissary canal (Fig. 1B). IJV was severely stenosed by the external compression of the elongated styloid process and the transverse process of the first vertebra (Fig. 1C-F). In contrast, the ipsilateral MEV and the connecting occipital vein were enlarged and drained into the external jugular vein, functioning as the sole collateral pathway of intracranial venous drainage (Fig. 1C).
Intraoperative photographs after positioning (A), scalp flap elevation (B), the identification of the occipital vein (C), identification of the MEV (D), denuding MEV (E), and dural opening (F). Intraoperative photographs after exposure to SCA and CN-V (G), mobilization of SCA (H), and transposition of SCA (I). *; Dacron felt
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Abbreviations in Fig. 2
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Sig. Sinus, sigmoid sinus; Trans. Sinus, transverse sinus; M., muscle; Sternocleidmast., sternocleidomastoid; Splen., splenius; Cap., capitis; Longiss., longissimus; Occip., occipital; V., vein; MEV, mastoid emissary vein; CN-V, trigeminal nerve; SCA, superior cerebellar artery; Sup., superior; Pet., petrosal
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Under general anesthesia, the patient was positioned in a park bench position on the left side, and an upside-down L-shaped skin incision was made above the transverse-sigmoid junction (Fig. 2A). The scalp flap was elevated inferomedially, and the sternocleidomastoid muscle was retracted anteriorly (Fig. 2B). The splenius capitis muscle was cut separately along the superior nuchal line and retracted inferomedially (Fig. 2C). The occipital vein was identified in the layer between the splenius capitis muscle and superior oblique muscle, and dissection was carefully performed along the occipital vein to identify the MEV and its foramen (Fig. 2D). Using a high-speed diamond drill, all bony structures were removed, leaving the intraosseous part of the MEV to reach the sigmoid sinus (Fig. 2E). The inferior margin of the transverse sinus was also exposed, securing a 1 x 2 cm entry space for the lateral supracerebellar approach (Fig. 2F). After opening the dura, the cerebellum was retracted inferiorly and medially, and the root of the trigeminal nerve and offending SCA were exposed (Fig. 2G). The SCA was transposed from the nerve by the insertion of Dacron felt pieces between the pons and the SCA (Fig. 2H and I).
Postoperative CT (A) and CTA (B) showing the insertion of the Dacron felt and the preservation of the collateral venous pathway.
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Postoperative CT also showed the preservation of the MEV and the connecting venous pathway (Fig. 3).