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|Year : 2019 | Volume
| Issue : 1 | Page : 159-162
Cresentic durotomy for midline posterior fossa lesions
Department of Neurosurgery, Dayanand Medical College, Ludhiana, Punjab, India
|Date of Web Publication||7-Mar-2019|
Dr. Ashwani Chaudhary
Department of Neurosurgery, Dayanand Medical College, Ludhiana, Punjab
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chaudhary A. Cresentic durotomy for midline posterior fossa lesions. Neurol India 2019;67:159-62
Harvey Cushing was the first to define posterior fossa surgery. Microsurgical techniques coupled with the usage of an operating microscope, the development of micro-instruments and an enhanced knowledge of micro-anatomy of the posterior fossa have revolutionized posterior fossa surgery. A midline suboccipitial craniectomy may be performed for lesions of the vermis, the postero-inferior pons and medulla, the fourth ventricle and foramen magnum, the midline cerebellar hemisphere and the pineal area [Figure 1] and [Figure 2]. After a midline suboccipital craniectomy, the dura is traditionally opened in a 'Y', 'U' or' V' shaped manner, but various neurosurgeons have attempted different methods of durotomy in order to minimize the complications.
|Figure 1: The posterior fossa after a suboccipital craniectomy in a cadaveric specimen. The dural impression of the (a) confluence of sinuses; (b) lateral sinus; (c) occipital sinus; (d) lateral limb of the occipital sinus; (e) foramen magnum posterior margin has been removed; (f) posterior arch of the C1 vertebra|
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|Figure 2: The posterior arch of the Atlas More Details is removed exposing the posterior fossa dura and extradural portion of the cervicomedullary junction|
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The standard midline suboccipital craniectomy includes a 'Y' shaped dural incision that results in ligation of the occipital sinus. With this dural opening, a very high incidence of postoperative complications (30%) have been reported in the literature like cerebrospinal fluid (CSF) leak, CSF infection, hydrocephalus, pseudomeningocele formation, and headache etc.
The various types of durotomies for a midline suboccipital craniectomy are described as:
| » The Conventional 'Y'-Shaped Durotomy|| |
The incision starts just inferior to the transverse sinus and runs obliquely to the midline, stopping near the occipital sinus in the midline. The opposite limb of the 'Y' limb is incised in a similar manner and connected at the midline. Bleeding from the occipital sinus can be controlled with cautery, obliquely placed haemostatic clips or suture ligatures. The vertical limb of 'Y' is opened and in case of bleeding, the dura can be tented with sutures. The vertical limb of the 'Y' is incised up to the foramen magnum to include the falx cerebelli, which is sometimes present in children [Figure 3].
|Figure 3: In a ‘Y’ shaped durotomy, the dural flap is retracted to expose the posterior fossa|
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| » The Crescent Durotomy|| |
The crescentic durotomy starts just lateral to the occipital sinus, inferior to the transverse sinus, with the convexity away from midline facing towards the sigmoid sinus. The dural incision further travels towards the foraman magnum, crossing the midline below the foraman magnum and reaching the upper border of C2 lamina on the opposite side. Just above the foraman magnum, the cresent durotomy incision encounters the lateral limb of the occipital sinus and the marginal sinus, which have to be eventually coagulated [Figure 4] and [Figure 5].
|Figure 4: Cresent durotomy: The arrow shows the edge of the dural incision|
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|Figure 5: Cresent durotomy: The dural flap is retracted to expose the posterior fossa|
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| » The Midline Vertical Durotomy|| |
After a midline suboccipital craniectomy, a vertical durotomy is made just parallel to the midline from just inferior to the transverse sinus to the foramen magnum. The free dural edges are then retracted with sutures to gain exposure to the posterior fossa [Figure 6] and [Figure 7].
|Figure 6: The linear durotomy: The arrow shows the edge of the dural incision|
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|Figure 7: The linear durotomy: The dural edges are retracted to expose the posterior fossa|
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| » Complications of Posterior Fossa in Relation to Durotomies|| |
Surgery in the posterior fossa is said to have a complication rate of as high as 30%, which in recent times has decreased owing to the modern microsurgical techniques. CSF leak is the most common complication in posterior fossa surgery. Other complications are CSF infection, hydrocephalus, postoperative headache, pseudomeningocele formation, bleeding etc.
A recent study by Panigrahi et al., shows that crescent durotomy has an edge over 'Y' durotomy as lesser number of patients developed a pseudomeningocele because of more probability of primary dural closure. The complications like surgical site haematoma, oedema, infections, cranial nerve deficits etc., however, remain the same in both the groups.
The occipital sinus is the smallest dural venous sinus. It communicates above with the confluence of sinuses and below with the marginal sinus or the vertebral venous plexus. The occipital sinus receives tributaries from veins of the hypoglossal canal, the diploic veins, the basilar plexus, and the occipital emissary vein. Anatomical variations of the occipital sinus include its deviation to one side to join the sigmoid sinus instead of running in the midline, its drainage into the sigmoid sinus, the duplication of the sinus, and the absence of the sinus. Occipital sinus becomes the major drainage channel when the lateral sinuses are hypoplastic. During midline suboccipital craniectomies, ligation of the occipital sinus may lead to postoperative intracranial hypertension in patients having a hypoplastic or rudimentary lateral sinus. Thus, it is advisable to get magnetic resonance venography done preoperatively to determine the status of the occipital, lateral and sigmoid sinus. The complications in relation to cerebellar lesions include cerebellar oedema, hydrocephalus, cerebellar haematoma and cerebellar mutism. The complications in relation to the fourth ventricular surgery include pneumocephalus and transient or permanent cranial nerve palsy, especially the 6th and 7th nerve.
| » Discussion|| |
The various types of durotomies described above have their pros and cons. The 'Y' shaped durotomy being the most popular and traditional approach, provides a better surgical exposure and a good control of the sinusoidal vessels near the foraman magnum in the event of any injury. It also gives a good access to the cerebellomedullary cistern for CSF drainage. The limitations of this technique are the requirement of ligation of the occipital sinus, requirement of a duroplasty, as well as more chances of CSF leak and formation of a pseudomeningocele. The crescent durotomy has a benefit over the 'Y' durotomy in reducing the need for a duroplasty, in providing a comfortable primary closure, with lesser chances of postoperative pseudomeningiocele formation or CSF leak. The crescent durotomy attempts to preserve the normal venous flow physiology, reducing the blood loss and venous hypertension by preserving the occipital sinus. The crescent durotomy, however, also has limitations in that the marginal sinus and the lateral limb of occipital sinus is sacrificed. It has limited surgical field exposure as compared to the 'Y' durotomy. It also has complications of postoperative CSF leak and pseudomeningocele formation, although these complications are much lesser than are seen in the conventional 'Y' durotomy., The midline vertical durotomy is usually applied for a select group of lesions in the posterior fossa located near the cerebellar vermis, floor of the fourth ventricle, and in the cortical region, as well as the telovelotonsilar, the tonsillomedullary and the lateral medullary segments. The advantages of the linear dural incision over the other types of durotomies are that it is quicker, the primary closure is easier, and there are lesser chances of CSF leakage, infection, pseudomeningocele formation, and lesser manipulation of brain parenchyma, although the amount of surgical exposure is less. A laterally extending venous lake may be opened with the risk of haemorrhage or venous air embolism, utilizing the midline approach.
| » Conclusion|| |
In this article, the authors have summarised the added advantages of a crescent durotomy over a conventional 'Y' durotomy in posterior fossa lesions in reducing the complications such as CSF leaks and pseudomeningocele formation. It helps in occipital sinus preservation and facilitates an easier primary dural closure. On the other hand, it is observed that the dural opening is limited and narrow. Duroplasty may also be required in a crescentic durotomy.
Another issue with it is that when the medial route of trans-cerebello-medullary fissure approach (the telo-velar approach) is adopted for lesions located in the fourth ventricle or near the cerebral aqueduct, or when a huge ventricular tumor extends into the lateral recess, a wide dural opening with removal of the tumor without any incision of the neural tissue is required at the level of foramen magnum. This exposes the inferior margin of the tonsil., A wide dural opening may facilitate the exposure at the level of foramen magnum to expose the inferior margins of the tonsil and the cerebellomedullary fissure on both sides.
In my opinion, in a standard midline craniectomy, any type of durotomy, 'Y' shaped, crescent or linear could be performed depending upon the size and site of lesion but a watertight dural closure along with replacement of the bone flap/cranioplasty in the same sitting is mandatory, as this approach definitely reduces the chances of postoperative complications such as CSF leaks, pseudomeningocele formation, postoperative headache, and wound dehiscence. If redo surgery is required, a bone flap or cranioplasty makes the repeat surgery easier and safe as it reduces dural adhesions, and there are less chances of injury to the dura and cerebellar tissue. The presence of a bone flap or a cranioplasty not only ensures safety from injuries but is cosmetically also better.
| » References|| |
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