Morphological Classification of the Medial Frontal Cortex Based on Cadaver Dissections: A Guide for Interhemispheric Approach

The medial frontal cortex (MFC) is a part of the medial surface of the frontal lobe situated in the rostral portion of the corpus callosum (CC). In a surgical interhemispheric approach (IHA), the MFC covers the anterior communicating artery (Aco) complex until the final stage of dissection. To clarify the anatomical relationship between the MFC and the Aco complex, and to facilitate orientation in IHA, we analyzed the morphological features of the MFC in number, size, and pattern of gyri from the medial surface of the hemisphere in the subcallosal portion using 53 adult cadaveric hemispheres. The mean width of the MFC excluding cingulate gyrus (MFCexcg) was 20.6 ± as mm in the subcallosal portion. MFCexcg consisting of 2, 3, 4, or 5 gyri were observed in 7.5%, 56.6%, 32.1%, or 3.8% of the hemispheres, respectively. Bilateral MFCexcg consisting of >2 gyri were observed in approximately 85% of the hemispheres. Therefore, in many cases, the dissection performed at 2 cm upward from the base of the straight gyrus (SG) or 3–4 gyri of the MFC is sufficient to safely reach the upper portion of the cistern of lamina terminalis located distal to the Aco complex in IHA. The MFC is a good landmark for intraoperative orientation in IHA.

Using of Fresh Cadaveric Cow Brain in the Microsurgical Training Model for Sulcal-Cisternal and Fissural Dissection

Objective

The aim of this experimental study was to evaluate the feasibility of using fresh cadaveric cow brain as in a training model for microsurgical dissection of sulcus, cisterns, and fissure.

Methods

Experimental microneurosurgical activities in this study were performed under the operating microscope. Bilateral sylvian cisterns, interhemispheric fissure, and hemispheric sulcus of the fresh cadaveric cow brain were used as an interested area for this experimental study. The dissection was continued reaching down to the floor of the cistern and total dissection of the middle cerebral artery inside the cisternal space. The suitability of a cow brain as a training model for sylvian fissure microdissection was evaluated as three groups; bad, good, and perfect.

Results

Ten uncovered fresh cadaveric cow brains were used in this experimental feasibility study. The suitability of the experiment for training model was evaluated as bad in (1) 10% of the fresh cadaveric cow brains. The suitability was found as good in (6) 60% of the procedures. In the remaining (3) 30% of the brain dissection, the suitability of the experiment was evaluated as perfect.

Conclusion

In conclusion, performing the sulcal, cisternal, and fissural dissection and protecting the neural and vascular tissue from the mechanical bruising effect of metallic microsurgical instruments are feasible as shown in this study. We believe that this training model will contribute to the practical micro-neurosurgery. Additionally, it provides adequate performance for the microsurgical intervention.

Exposure of Dural Venous Sinuses: A Review of Techniques and Description of a Single-piece Troughed Craniotomy

Intracranial lesions along the falx and tentorium often require exposure of a dural venous sinus. Craniotomies that cross a sinus should maximize exposure while minimizing the risk of sinus injury and provide a cosmetically appealing result with simple reconstruction techniques. 

We describe the published techniques for exposing dural venous sinuses, and introduce a new technique for a single-piece craniotomy exposing the superior sagittal sinus or transverse sinus using drilled troughs.

A review of the literature was performed to identify articles detailing operative techniques for craniotomies over dural venous sinuses. Our troughed craniotomy for dural sinus exposure is described in detail as well as our experience using this technique in 82 consecutive cases from 2007-2015.

Five distinct techniques for exposure of the dural venous sinus were identified in the literature. In our series of patients undergoing a trough craniotomy, there were no sinus injuries despite a range of various locations and pathology along the sagittal and transverse sinuses. Our technique was found to be safe and simple to reconstruct compared to other techniques found in the literature.

A variety of different techniques for exposing the dural venous sinuses are available. A single-piece craniotomy using a trough technique is a safe means to achieve venous sinus exposure with minimal reconstruction required. Surgeons should consider this method when removing lesions adjacent to the falx or tentorium. 

Astroglial-Mediated Remodeling of the Interhemispheric Midline Is Required for the Formation of the Corpus Callosum

The corpus callosum is the major axon tract that connects and integrates neural activity between the two cerebral hemispheres. Although ∼1:4,000 children are born with developmental absence of the corpus callosum, the primary etiology of this condition remains unknown. Here, we demonstrate that midline crossing of callosal axons is dependent upon the prior remodeling and degradation of the intervening interhemispheric fissure. This remodeling event is initiated by astroglia on either side of the interhemispheric fissure, which intercalate with one another and degrade the intervening leptomeninges. Callosal axons then preferentially extend over these specialized astroglial cells to cross the midline. A key regulatory step in interhemispheric remodeling is the differentiation of these astroglia from radial glia, which is initiated by Fgf8 signaling to downstream Nfi transcription factors. Crucially, our findings from human neuroimaging studies reveal that developmental defects in interhemispheric remodeling are likely to be a primary etiology underlying human callosal agenesis.

Supratentorial extraventricular WHO grade III (anaplastic) ependymoma 17 years after total removal of WHO grade II ependymoma of the fourth ventricle

We report a WHO grade III ependymoma of the supratentorial interhemispheric fissure and grew to form a large mass with anaplastic transformation without local recurrence 17 years after the total removal of a fourth ventricular WHO grade II ependymoma. We emphasize the necessity of long-term follow-up, even in benign ependymomas.

Distortion of the anterior part of the interhemispheric fissure: significance and implications for prenatal diagnosis

In order to illustrate the significance of a new anatomical finding, distortion of the interhemispheric fissure (DIHF) associated with impacted medial borders of the frontal lobes, we report a retrospective observational study of 13 fetuses in which DIHF was identified on prenatal imaging. In 10 cases there were associated anatomical anomalies, including mainly midline anomalies (syntelencephaly (n=2), lobar holoprosencephaly (n=1), Aicardi syndrome (n=2)), but also schizencephaly (n=1), cortical dysplasia (n=1) and more complex cerebral malformations (n=3), including neural tube defect in two cases. Chromosomal anomaly was identified in two cases, including 6p deletion in a case without associated central nervous system anomalies and a complex mosaicism in one of the cases with syntelencephaly. In two cases, the finding was apparently isolated on both pre- and postnatal imaging, and the children were doing well at follow-up, aged 4 and 5 years. The presence of DIHF on prenatal imaging may help in the diagnosis of cerebral anomalies, especially those involving the midline. If DIHF is apparently isolated on prenatal ultrasound, magnetic resonance imaging is recommended for careful analysis of gyration and midline, especially optic and olfactory structures. Karyotyping is also recommended.