Indications
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Cavernous malformations are “low-pressure” vascular malformations that typically come to clinical attention because of seizures or acute hemorrhage. With widespread use of noninvasive axial imaging, many cavernous malformations are now being diagnosed incidentally.
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Surgery is recommended in symptomatic patients with seizures or after at least one symptomatic bleed. In patients with symptomatic brainstem and thalamic cavernous malformations, surgery is usually recommended if the lesion comes to a pial or ependymal surface.
Planning and positioning
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In planning surgery for a cavernous malformation, the main factors crucial to the success of the operation are the location of the lesion and its relationship to surrounding eloquent structures. Positioning and approaches for supratentorial cortical and subcortical cavernous malformations do not differ from basic craniotomies for other neoplastic or vascular supratentorial lesions. We discuss only the basic surgical techniques for the resection of supratentorial cavernous malformations. Resection of brainstem and thalamic cavernous malformations poses specific problems and technical pitfalls that are discussed in more detail.
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In preparing patients for resection of brainstem and thalamic cavernous malformations, proper counseling is important to alert them to the possibility of transient worsening of symptoms that mimic prior bleeding episodes. If the operation is conducted correctly, most patients return to their preoperative baseline after a possible transient postoperative worsening.
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Planning of the correct approach depends on the location of the cavernous malformation itself; the pattern of bleeding, which may have opened a “surgical corridor”; and the location at which the cavernous malformation approaches the pial or ependymal surface. Location of associated developmental venous anomalies is also a very important aspect in the planning of the correct approach. We believe strongly, as do other authors, that every attempt must be made to preserve the associated developmental venous anomaly (which is present in virtually all brainstem cavernous malformations even when not shown on preoperative magnetic resonance imaging [MRI]). Damage of the developmental venous anomaly invariably results in a venous infarct and poor outcome.
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Ideally, we prefer to operate 2 to 3 weeks after a symptomatic bleed. Operation within this time frame allows for partial liquefaction of the hematoma, limiting the mechanical trauma related to the surgery. In such cases, the liquefied hematoma allows for easy internal decompression with minimal trauma. We try to avoid surgery months after a symptomatic bleed because organization of the hematoma leads to more adhesions with the surrounding hemosiderin-stained brainstem parenchyma and increases trauma related to resection. Despite the brainstem location, immediate clinical improvement can be observed after resection of some large “hemorrhagic” cavernous malformations in which the symptoms are partially related to mechanical displacement and compression of the surrounding parenchyma rather than destruction.
Figure 31-1:
A simple principle to follow in deciding which approach to choose is the two-point method. In deciding the most superficial location of the cavernous malformation, T1-weighted images must be used instead of T2-weighted images. On T2 images, a “blooming” artifact gives the false impression of a larger extension and superficiality of the cavernous malformation.
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Frameless stereotaxy registered to the focus of the surgical microscope is very helpful to provide real-time feedback during surgery. It is particularly useful, in combination with intraoperative monitoring and mapping, to identify the point of entry and initial incision in cases in which, despite suggestion on MRI of a superficial extension, exploration of the outer surface of the brainstem or thalamus does not provide direct or indirect clues regarding the exact location of the cavernous malformation.
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Many thalamic and caudate cavernous malformations are adjacent to the ventricular surface. For these lesions, we prefer a contralateral transcallosal approach with the head parallel to the floor and the symptomatic side up. In such a manner, the surgeon takes advantage of gravity, which drops the ipsilateral (to the approach) hemisphere away from the falx. Having the head parallel to the floor allows for the surgeon’s hands to be side by side in a more physiologic working position. The contralateral approach also affords a more direct trajectory to the lesion.
Figure 31-2:
In the contralateral transcallosal approach, the ipsilateral (to the approach) hemisphere “falls” away from the falx by gravity and allows the surgeon to work without any additional brain retraction ( C and D ). In addition, the contralateral approach with the head positioned as in A and B provides a more direct and optimal (trajectory B in D ) trajectory to the lesion than an ipsilateral (to the target lesion) approach (trajectory A in D ).
Figure 31-3:
Various approaches are available when treating cavernous malformations of the brainstem. The choice of the approach depends on the location and superficiality of portions of the cavernous malformation, the patient’s preoperative deficits, the location of associated venous developmental anomalies, and the surgeon’s preference and level of comfort with one approach over the other.Related posts:
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