A taxonomy for brainstem cavernous malformations: subtypes of medullary lesions

OBJECTIVE Medullary cavernous malformations are the least common of the brainstem cavernous malformations (BSCMs), accounting for only 14% of lesions in the authors' surgical experience. In this article, a novel taxonomy for these lesions is proposed based on clinical presentation and anatomical location. METHODS The taxonomy system was applied to a large 2-surgeon experience over a 30-year period (1990 & ndash;2019). Of 601 patients who underwent microsurgical resection of BSCMs, 551 were identified who had the clinical and radiological information needed for inclusion. These 551 patients were classified by lesion location: midbrain (151 [27%]), pons (323 [59%]), and medulla (77 [14%]). Medullary lesions were subtyped on the basis of their predominant surface presentation. Neurological outcomes were assessed according to the modified Rankin Scale (mRS), with an mRS score <= 2 defined as favorable. RESULTS Five distinct subtypes were defined for the 77 medullary BSCMs: pyramidal (3 [3.9%]), olivary (35 [46%]), cuneate (24 [31%]), gracile (5 [6.5%]), and trigonal (10 [13%]). Pyramidal lesions are located in the anterior medulla and were associated with hemiparesis and hypoglossal nerve palsy. Olivary lesions are found in the anterolateral medulla and were associated with ataxia. Cuneate lesions are located in the posterolateral medulla and were associated with ipsilateral upper-extremity sensory deficits. Gracile lesions are located outside the fourth ventricle in the posteroinferior medulla and were associated with ipsilateral lower-extremity sensory deficits. Trigonal lesions in the ventricular floor were associated with nausea, vomiting, and diplopia. A single surgical approach was preferred (> 90% of cases) for each medullary subtype: the far lateral approach for pyramidal and olivary lesions, the suboccipital-telovelar approach for cuneate lesions, the suboccipital-transcisterna magna approach for gracile lesions, and the suboccipital-transventricular approach for trigonal lesions. Of these 77 patients for whom follow-up data were available (n = 73), 63 (86%) had favorable outcomes and 67 (92%) had unchanged or improved functional status. CONCLUSIONS This study confirms that the constellation of neurological signs and symptoms associated with a hemorrhagic medullary BSCM subtype is useful for defining the BSCM clinically according to a neurologically recogniz- able syndrome at the bedside. The proposed taxonomical classifications may be used to guide the selection of surgical approaches, which may enhance the consistency of clinical communications and help improve patient outcomes.

Automated summary

This article proposes a novel taxonomy for medullary cavernous malformations based on clinical presentation and anatomical location. A large 2-surgeon experience over a 30-year period was used to apply the taxonomy system to 551 patients who underwent microsurgical resection of brainstem cavernous malformations. Five distinct subtypes were defined for the medullary lesions, and surgical approaches were selected based on the subtype. The study confirms that the proposed taxonomy can improve clinical communication and patient outcomes.