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Brainstem Cavernous Malformations: Anatomical, Clinical, and Surgical Considerations

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Brainstem Cavernous Malformations: Anatomical, Clinical, and Surgical Considerations Neurosurg Focus 29 (3):E9, 2010 Brainstem cavernous malformations: anatomical, clinical, and surgical considerations GIULIANO GILIBERTO , M.D.,1,6 DESIREE J. LANZINO , PH.D., 2 FELIX E. DIEHN , M.D.,3 DAVI D FACTOR , M.S.,4 KELLY D. FLE mm IN G , M.D.,5 AN D GIUSE pp E LANZINO , M.D.6 1Operative Unit of Neurosurgery, Nuovo Ospedale Civile, Modena, Italy; and Departments of 2Physical Medicine & Rehabilitation, 3Radiology, 4Media Support Service, 5Neurology, and 6Neurologic Surgery, Mayo Clinic, Rochester, Minnesota Symptomatic brainstem cavernous malformations carry a high risk of permanent neurological deficit related to recurrent hemorrhage, which justifies aggressive management. Detailed knowledge of the microscopic and surface anatomy is important for understanding the clinical presentation, predicting possible surgical complications, and formulating an adequate surgical plan. In this article the authors review and illustrate the surgical and microscopic anatomy of the brainstem, provide anatomoclinical correlations, and illustrate a few clinical cases of cavernous mal- formations in the most common brainstem areas. (DOI: 10.3171/2010.6.FOCUS10133) KEY WOR D S • cavernous malformation • brainstem • safe entry zone • developmental venous anomaly ITH recent advances in imaging, surgical tech- cation, we will describe and illustrate the specific surface niques and electrophysiological monitoring, anatomy encountered by the surgeon after exposure of CMs of the brainstem can be treated safely with the particular area and briefly discuss the pros and cons Wresection. To maximize the chances of effective and safe of the various routes. Various approaches can be used to removal, a thorough knowledge of the surface and intrin- remove a given lesion, and multiple considerations play sic brainstem anatomy, as well as of the clinical and sur- a role in choosing the correct approach. These include gical correlates, is critical. In this article, we review and the following: clinical presentation, lesion location, area illustrate the anatomy of the brainstem and correlate it to which the lesion comes closest to the surface, clini- with clinical considerations in relation to the most com- cal functions of specific areas, pattern and distribution mon locations of CMs in this area. Moreover, we provide of associated hemorrhage, relationships to the adjacent clinical examples and summarize some general technical DVA, and last but not least the degree of comfort of the principles to guide surgery in this challenging area. individual surgeon with a specific approach. For educa- tive and logistical purposes we will try to schematize the surgical considerations as they relate to a specific area. It General Clinical and Surgical Considerations is important, however, to understand that no dogma exists Various surgical approaches are available to gain ac- and the approach as well as the surgical strategy must be cess to the different sections of the brainstem (Fig. 1). A tailored to the particular characteristics of the individual comprehensive description of these well-established ap- patient. proaches is beyond the scope of this review. For each lo- There is lack of agreement about the indications for surgery in patients with brainstem CMs. We usually recommend resection for symptomatic CMs after a re- Abbreviations used in this paper: BA = basilar artery; CM = cent first hemorrhage for superficial lesions. We tend to cavernous malformation; CN = cranial nerve; DVA = developmen- tal venous anomaly; FOZ = frontoorbitozygomatic; MLF = medial be more aggressive in patients with hemorrhagic lesions longitudinal fasciculus; PCA = posterior cerebral artery; PICA = if the hemorrhage extends beyond the boundaries of the posterior inferior cerebellar artery; SCA = superior cerebellar artery; CM. It has been our anecdotal experience that these pa- UMN = upper motor neuron. tients have a higher risk of bleeding. Neurosurg Focus / Volume 29 / September 2010 1 Unauthenticated | Downloaded 09/25/21 01:11 PM UTC G. Giliberto et al. operative monitoring, structures such as the corticospinal tract in the cerebral peduncle, CN nuclei (CNs VII, IX, X, and XII), the facial colliculus, and hypoglossal and vagal trigones on the floor of the fourth ventricle can be identified.51 Frameless stereotaxy registered to the focus of the surgical microscope is also very helpful, especially when the CM is hidden under a very thin layer of normal- appearing parenchyma. The goal of surgery for brainstem CMs is radical re- moval of the lesion. Partial removal is associated with a persistent and probably higher risk of recurrent hemor- rhage from the residual lesion. We recommend delaying surgery after a symptomatic hemorrhage if possible for 2–3 weeks. This delay allows for partial liquefaction of the hematoma, providing a natural buffer that diminishes sur- gery-related trauma. We also try to avoid operating months after a symptomatic bleed when hematoma retraction and organization lead to tight adherence between the CM and the surrounding parenchyma, which increases the likeli- hood of mechanical trauma from surgical manipulation. Brainstem CMs are usually removed through an in- cision smaller than the lesion itself. This makes internal 30 FIG. 1 Schematic drawing illustrating the most common surgical ap- decompression and piecemeal removal necessary (Fig. proaches used for different areas of the brainstem. 3). “En bloc” resection is usually neither safe nor feasible in this location. In contrast to the situation with supraten- Surgery for brainstem CMs requires careful preop- torial CMs, after resection of a brainstem CM the hemo- erative planning. Cavernous malformations compress and siderin-stained parenchyma is not disturbed and is left in displace the surrounding parenchyma rather than infil- situ. Every attempt must be made to preserve any associ- trating it. If the malformation abuts the pial or ependymal ated DVA 30,43,46,48 (Fig. 4); the presence of a DVA should surface, it provides a direct and safe entry route5 (Fig. 2). be suspected even when the preoperative MR imaging When the lesion is deep and separated from the surface by does not show one. Sacrifice of the DVA will invariably a thin parenchymal layer, surgery can still be performed lead to a venous infarct with disastrous clinical seque- safely by following a “safe entry zone;”5,15,28,46,49,52 these lae.32,46,50,53 Developmental venous anomalies are usually are relatively safe but narrow surgical corridors into the absent in patients with familial CMs.44 brainstem parenchyma where “critical neural structures are sparse and no perforating arteries are encountered.”49 Intraoperative monitoring is helpful in identifying Anatomical, Clinical, and Surgical Considerations safe entry zones especially in the presence of large un- in Relation to Common Brainstem Locations derlying lesions that distort normal anatomy. With intra- Midbrain: Internal and Functional Anatomy The anterior midbrain contains the crus cerebri, which are composed of cortical projections to the brainstem and spinal cord (Fig. 5). Projections to the pontine nuclei from the parietal, occipital, and temporal lobes are found later- FIG. 2. Intraoperative photograph showing a posterolateral CM of the left medulla abutting the pial surface. The CM was exposed through a posterior suboccipital approach after elevation of the ipsilateral tonsil. The PICA loop and the vertebral artery (deeper in the left corner) are FIG. 3. Artist’s illustration showing internal emptying of the same CM visible. The superficial portion of the CM in this case provided a natural as in Fig. 2 and piecemeal removal with a pituitary forceps through a and atraumatic entry route. small opening. 2 Neurosurg Focus / Volume 29 / September 2010 Unauthenticated | Downloaded 09/25/21 01:11 PM UTC Brainstem cavernous malformations pattern that occurs in classic decorticate posturing. The red nucleus exerts its influence on the musculoskeletal system through the rubrospinal tract, which descends to the con- tralateral spinal cord. The medial lemniscus carries prop- rioception, vibration, and discriminative touch information from the contralateral spinal cord to the ventral posterior lateral nucleus of the thalamus. In more caudal sections, the decussation of the su- perior cerebellar peduncle lies centrally and medially in- stead of the more rostrally located red nucleus. Continuing dorsally, CN nuclei are located medially and the spinothalamic tract (anterolateral system) later- ally. The CN nuclei found in the midbrain are the oculo- motor nuclear complex and Edinger-Westphal nucleus rostrally and the trochlear nucleus caudally. The nuclei of CN III, the oculomotor nuclei and Ed- inger-Westphal nucleus, are found primarily at the level FIG. 4. Intraoperative photograph obtained after resection of the CM of the superior colliculus. The oculomotor nuclei supply shown in Figs. 2 and 3. A typical DVA is visible along the inferior wall of the surgical cavity although no clear-cut evidence of a DVA was visible the somatic innervation to the superior, inferior, and me- on the preoperative MR images. dial rectus; the inferior oblique; and the levator palpebrae muscles. The Edinger-Westphal nucleus supplies the para- ally, whereas frontal projections are found medially. At the sympathetic innervation to the intraocular muscles for the center of the crus cerebri is the corticospinal tract and me- accommodation reflex (pupillary constriction and ciliary dial to that the corticobulbar tract.
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