Crescent durotomy for midline posterior fossa lesions
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.253637
Source of Support: None, Conflict of Interest: None
Keywords: Crescent durotomy, conventional durotomy, pseudomeningiocoele
The conventional midline suboccipital craniectomy, the standard approach for posterior fossa lesions, involves ligation of the occipital sinus. In prone position (adapted during surgery), variable degrees of neck flexion and raised intrathoracic pressures increase venous pressure/hypertension. This could be worsened by disconnecting the occipital sinus, as is done during the conventional “Y” dural opening technique., Blockage of the jugular system by the lesion and a predominant venous drainage of the tumor into the occipital sinus could also result in a catastrophic venous hemorrhage/edema on ligation of this sinus.,,,,,,, This may have serious consequences, such as a malignant cerebellar bulge, resulting in significant morbidity and mortality.
Other postoperative sequelae that could occur from ligation of the occipital sinus include hydrocephalus, cerebrospinal fluid (CSF) leak, and a pseudomeningiocoele formation., The possible mechanism may be impaired venous drainage resulting in raised interstitial pressure in the posterior fossa leading to failure of CSF re-absorption., Therefore, the standard practice of venous pathway preservation, as prevalent elsewhere in the cranium, should also be attempted in the posterior fossa. We have previously proposed a new technique where the sinus complex is preserved by the use of a crescent durotomy. In the current study, we compared the postsurgical complications that occurred while using the conventional “Y” duratomy with those that occurred while using the crescent durotomy in patients with posterior fossa lesions who underwent a midline suboccipital craniectomy.
Between January 2011 and December 2015, 104 consecutive patients posted for midline suboccipital craniectomy for a posterior fossa tumor at a tertiary referral centre in south India formed the study population. Demographic, clinical, surgical, and outcome data of all patients was collected prospectively. An informed written consent was obtained from all the participants, and the study was approved by the Institutional Ethics Committee.
All patients underwent a preoperative contrast magnetic resonance imaging (MRI) to document the status of the sigmoid sinus and its drainage pattern. The choice of the durotomy was made based on the preference of the operating surgeon.
All patients were operated in the prone position. A conventional midline suboccipital vertical skin incision was followed by muscle dissection exposing the subocciput. A midline suboccipital craniectomy was done in all the cases. In patients operated by using the conventional “Y” incision, the dura was opened in the manner described previously., In cases operated upon by using the “crescent” approach, a crescent-like dural incision (with the convexity being away from midline) that curves along one side of the occipital sinus and crosses the midline below the foramen magnum was used. The incision inevitably ran across the ipsilateral marginal sinus just above the foramen magnum. This part of the marginal sinus was coagulated and sectioned. The incision extended across the midline to the opposite side at the upper border of C2 lamina. The dura along with the occipital was reflected to the contralateral side using stay sutures [Figure 1]. The side of the crescent incision was opposite (mostly left side) to the dominant sigmoid sinus, as assessed using the preoperative contrast MRI scan. A detailed description of the surgical technique has been reported previously.
After tumor excision, the dural closure was done in both the approaches and a duroplasty was performed, if needed. A standard craniotomy was used in all the patients and was followed by a standard layered wound closure. None of the patients underwent a cranioplasty. All cases were assessed for study endpoints such as the need for a duroplasty and for the occurrence of on-table complications (cerebellar hemorrhage or tumor bleed). Data regarding the postoperative complications (hydrocephalus, CSF leaks, and pseudomeningiocoele formation) was collected during the immediate postoperative stay of the patient.
After confirming the normal distribution of the data, all continuous variables were expressed as mean ± standard deviation (SD) and all categorical variables were reported as frequencies or percentages, as appropriate. Comparison of quantitative variables between the durotomy groups was done using Student's T-test for independent samples. For comparing the categorical data, the Chi-square test was performed. A probability value (P value) less than 0.05 was considered statistically significant and reportable. All statistical calculations were done using SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) version 17.
The current study was designed, executed, and reported in adherence to the CONSORT 2010 guidelines.
Of the 104 patients who formed the study population, 39 (37.5%) were women. While 75 patients underwent a crescent durotomy, the remaining underwent the conventional “Y” durotomy. There was no difference between the groups regarding their age (23.2 ± 18.4 years vs 28.9 ± 23.3 years; P = 0.192). There were no significant differences between the patients undergoing either of the techniques with regards to their presenting complaints such as headache (84.0% vs 75.9%; P = 0.398), blurring of vision (37.3% vs 48.3%; P = 0.374), ataxia (68.0% vs 79.3%; P = 0.336), and cerebellar signs (77.3% vs 82.8%; P = 0.605). Similarly, there were no differences between the groups with regard to their presentation with cranial nerve deficits (10.7% vs 10.3%; P = 1.000) and hydrocephalus (65.3% vs 65.5%; P = 1.000). [Table 1] summarizes the comparison between the groups regarding their presurgical variables.
During the surgery, the necessity of an extraventricular drainage was similar in both the groups (32.0% vs 34.5%; P = 0.819). Among the postsurgical complications, there were no differences between the groups pertaining to surgical site hematoma (2.7% vs 3.4%; P = 1.000) and edema (1.3% vs 0.0%; P = 1.000). The groups also had a similar incidence of postsurgical subdural hygroma (1.3% vs 3.4%; P = 0.482), CSF leak (1.3% vs 6.9%; P = 0.187), and cranial nerve deficit (4.0% vs 6.9%; P = 0.617). However, more number of patients who underwent a “Y” durotomy had postoperative pseudomeningiocoele formation (2.7% vs 17.2%; P = 0.017). [Table 2] summarizes the comparison between the groups for their intra- and postsurgical variables.
In the current prospective study of 104 consecutive posterior fossa operations performed through a midline suboccipital craniectomy at a single institution, we report that the “crescent” durotomy significantly reduces the incidence of postoperative pseudomeningiocoele formation than the conventional “Y” durotomy.
The incidence of pseudomeningiocoele (17.2%) formation in the current study is similar to that reported in a large study (16.5%) by Smith et al. Pseudomeningiocoele formation and CSF leak are more often associated with a midline posterior approach as opposed to the lateral posterior fossa approaches. The crescent technique adopts a lateral entry and preserves the occipital sinus. This probably explains the low incidence of these complications with this technique. Similarly, a primary dural closure is associated with less CSF leak compared to the performance of a duroplasty. A duroplasty in the crescent approach was often not required when the results of the procedure were compared to that of the conventional “Y” technique, which probably explains the low rates of pseudomeningiocoele formation with the crescent technique. The dural venous bleed was also significantly lesser utilizing the cresent technique by avoiding the prominent occipital sinus (also more often the right marginal sinus). Reduction in the need to coagulate the dura allowed for a higher incidence of its primary closure. Though it was not possible to quantify the reduction in the blood loss during the dural opening, it was perceived by the operating surgeon, that the amount of blood loss with a crest dural opening was a lot less and was reflected in the reduced use of dural coagulation., It was also important to note that the direction of the convexity of crescent approach of dural opening, and the fact that it was usually performed on the left side (on the side opposite the dominant sigmoid sinus), made it more convenient for the surgeon (as most of the surgeons are right handed), enabling a dexterous opening of the dura.
Smith et al., have recently suggested that a pseudomeningiocoele formation is a common complication after posterior fossa surgery. A postoperative ventriculomegaly heralds the presence of obstruction of the CSF pathway; the resultant CSF under pressure in the posterior fossa subarachnoid spaces makes its way through the weakest point, which is the midline dural incision and also the midline suboccipital craniotomy, fascial and skin incision. In this situation, a temporary CSF diversion procedure often helps in curbing the CSF leak through the wound/and/or pseudomeningocoele formation in the interm period while the wound heals. In the absence of ventriculomegaly, a temporary use of a lumbar drain often leads to an earlier clinical resolution of this complication. Further research should be performed to establish the most effective treatment strategy for preventing this morbidity. Since prevention is better than cure, a crescent durotomy may perhaps be the ideal way to prevent a pseudomeningiocoele formation during the performance of a midline suboccipital craniotomy/craniectomy.
Strengths and limitations
The current study, a single-center experience, helped us in collecting content-specific data that was more pertinent to the research hypothesis. Results of the current study reflect findings that have emerged from a consistent environment and standardised patient-care protocols, with little scope for variability that is often attributed to different models of care at different institutions in multicentre studies. We included univariate comparisons; the findings of our study, therefore, must be interpreted with caution. The findings of the study, however, seem to be reproducible backed by a plausible clinical reasoning.
A “crescent” durotomy is a novel dural-opening technique which attempts to preserve the normal venous flow physiology. Crescent durotomy reduces the need for a duroplasty, thus facilitating a comfortable primary closure, and reducing the risk of postoperative pseudomeningiocoele formation.
We are thankful for the contribution of Dr. Shyam Sunder Krishna for his contribution in the pilot phase of the current study and in the conduction of the current study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
[Table 1], [Table 2]