Surgery Of Olfactory Groove Meningiomas Biology Essay

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Olfactory groove meningiomas account for 8 to 13 % of all intracranial meningiomas.(1,3,5,13,14) It arise in the midline over the cribriform plate and frontosphenoid suture and occupy the floor of the anterior cranial fossa extending all the way from the the cresta galli to the tuberculum sellae.(6.14) As the tumor extends posteriorly it pushes the optic nerve and chiasm downwards and posteriorly, this will differentiate OGM from tuberculum sellae meningiomas which displace the optic nerves superolaterally and thus occupies a subchiasmal position.(15,24,29) Different surgical approaches are described for resection of OGMs including the traditional frontal or bifrontal approach,(4,9) the pterional approach,(5,13,31) the more aggressive approaches for tumors extending in the paranasal sinuses and orbits including the transbasal approach,(23) the subcranial approach,(3,10) the frontoorbital approach,(8) frontal or bifrontal craniotomy combined with orbital or nasal osteotomies(29,30) and craniofacial resection.(26,27) Contrary to the aggressive surgical approaches the endoscopic glabellar approach is also described.(16) Perneczky and his collegues(25) advocated the minimally invasive supraorbital minicraniotomy for a variety of skull base tumors. Surgical resection of small to medium-sized OGMs is not difficult. Large tumors involving the anterior cerebral complex present surgical challenge and needs extensive microsurgical dissection.(29)

METHODS

Between 2000 and 2009, twenty three patints with olfactory groove meningiomas were operated. Among the patients were 15 females and 8 males. The age ranged from 26 years to 65 years with a mean of 45.2 years (table I). Presenting symptoms and signs are described in table (II). Headache, papillodema, anosmia were the most common presenting manifestations, followed by mental manifestations and diminution of vision. Five patients have epilepsy as the first presenting symptom.

Radiological findings

Computed tomography (CT) and magnetic resonance imaging (MRI) were done for all patients. Tumor diameter varied from 3.3 to 6.1 cm (mean 4.7 cm). Three patients had undergone previous operation elsewhere and presented to us as recurrent tumors. Hyperostosis was present in 4 patients, calcification in 9 patients and encasement of the anterior cerebral artery complex in 5 patients. Tumor extension to the paranasal sinuses was observed in 6 patients.

Surgical technique

The patient is placed in the supine position. In large tumors more than 4 cm we request from the anesthetist to insert a lumber drain which is opened after craniotomy to drain CSF to minimize retraction. The skin incision is made just behind the hair line from zygoma to zygoma. The scalp is reflected anteriorly. A pericranial flap is elevated and care taken to keep it intact for later repair of the anterior skull base. A craniotomy is performed extending anteriorly as close as possible to the orbital roof. The basal line of the craniotomy usually involves the frontal air sinuses, the mucus membrane is completely removed and sinus cranialized. The dura is opened parallel to the base and the superior sagittal sinus is ligated and cut at the cecal foramen and the falx is cut to open up the surgical field. The tumor capsule was first opened and tumor debulked with the help of CUSA. Tumor resection is done in piecemeal fashion. Effort is made to devascularise the tumor at the skull base to facilitate resection with minimal blood loss. The dural origin of the tumor is then resected and if hyperostosis is present it is removed by diamond drill. If there is paranasal sinus involvement, the sinus is entered and tumor resected from above. The skull base is then reconstructed using pericranial flaps and or temporalis fascia in the frontal and ethmoidal air sinuses if they were opened.

Extent of tumor resection

The extent of tumor resection was classified according to the Simpson classification.(28) Grade 1 indicates total tumor resection with excision of the infiltrated dura; grade2 indicate total tumor resection and coagulation of the dural attachment; grade 3 indicates gross total removal without excision of dural attachments or extradural extension; grade4 indicate subtotal tumor resection. In 20 patients tumors were totally removed (Simpson grade 1 and 2) and in three patients tumors were subtotally removed (Simpson grade 3 and 4). The cause for incomplete tumor resection was inability to separate the tumor from the anterior cerebral artery and these patients were referred to radiosurgery doctor for further management.

Surgical outcome

Immediate postoperative CT scan was done in all patients. The most common finding was subdural hygroma in 9 patients especially in large tumors and it disappeared spontaneously in the follow up period. Tumor bed hematoma occurred in three patients and needed surgical evacuation in only one patient who was awaken from anaethesia in a stuperosed condition and he improved after evacuation. Postoperative generalized seizures occurred in 5 patients and were controlled with appropriate antiepileptic medication. CSF rhinorrhea occurred in three patients and was successfully controlled by repeated lumbar drain and antibiotic coverage. Wound infection occurred in 3 patients and responded well to proper antibiotic treatment. Olfaction was lost in all but 3 patients in whom tumor resection was incomplete (table III).

Histopathological diagnosis

The pathology in all patients was Grade I meningiomas (World Health Organization grading). The most common subtype was meningothelial meningioma (14 cases), followed by psamomatous meningioma (6 cases), and fibrous meningioma (3 cases).

Tumor recurrence

Tumor recurrence occurred in one patient, she was a young female operated 2003 with Simpson grade 2 excision. During the routine follow up in 2008 tumor recurrence was seen and reoperation was done with total excision of the tumor which was of the meningothelial type.

Table I: Summary of 23 patients

Patient

Age

Gender

Maximum diameter

Extent of resection

1

44

F

5.2

Total

2

26

F

5.7

Total

3

42

F

4.8

Total

4

53

F

6.1

Total

5

65

M

3.9

Total

6

51

M

5.1

Total

7

39

F

6.1

Subtotal

8

62

F

3.7

Total

9

40

F

4.4

Subtotal

10

56

M

4.8

Total

11

47

F

4.2

Total

12

38

M

5.5

Total

13

34

F

4.8

Subtotal

14

35

M

3.3

Total

15

34

F

4.1

Total

16

43

F

3.6

Total

17

42

F

3.9

Total

18

54

M

5.2

Total

19

43

M

5.5

Total

20

49

F

5.2

Total

21

46

M

3.7

Total

22

52

F

5.1

Total

23

46

F

5.4

Total

Table II: Symptoms and signs No. of patients

Headache

21

Papillodema

11

Olfactory impairment

11

Visual impairment

10

Mental changes

10

Epilepsy

5

Optic atrophy

4

Foster Kennedy

2

Table III: Operative complications

Complication

No. of patients

CSF rhinorrhea

3

Tumor bed hematoma

3

Anosmia

20

Wound infection

3

Partial optic nerve injury

1

Seizures

5

Fig 1: Upper and lower left: axial CT scan of a case of olfactory groove meningioma (notice the calcification): sagittal and coronal MRI of the same case, lower right: postoperative CT scan after total removal.

Fig 2: Left and middle: axial and coronal MRI of a case of olfactory groove meningioma, right: postoperative CT scan after total removal.

Fig 3: Upper left: axial CT scan of a case of olfactory groove meningioma (notice the calcification), upper right: sagittal MRI of the same case (notice the paranasal sinus invasion), lower: postoperative CT scan after total removal.

Fig 4: Upper: axial CT scan of a case of olfactory groove meningioma (notice the calcification), middle:axial and coronal MRI of the same case (notice the paranasal sinus invasion) , lower: postoperative CT scan after total removal.

DISCUSSION

Surgical approaches

Several surgical approaches have been used for resection of the OGMs ranging from extensive skull base approaches to minimally invasive endoscopic approaches.(3,5,9,13,16,25)

The bifrontal approach proposed by Tonnis in 1938,(30) is recommended by others for removal of large OGMs.(5,9,19) It is proposed that this approach allows the least amount of retraction and gives direct access to almost both sides of the tumor.(5,19) The bifrontal approach allows also early tumor devascularisation and gives good exposure for skull base reconstruction.(5,10) The disadvantages include division of the superior sagittal sinus which contributes to post operative frontal lobe edema and brain swelling, the previous concept that the anterior third of the sinus can be safely ligated is no longer true.(13) The second disadvantage is that the important vascular structure and optic apparatus are not visualized except after excision of a big bulk of the tumor.(13,29) In our study we were able to counter these disadvantages by very anterior ligation of the sinus at the foramen cecum and carefull microsurgical dissection of the posterior part of the tumor after good study of the MRI T2weighted to see the relation of the anterior cerebral artery complex to the tumor.

The pterional approach has the advantage of early identification and securing the neurovascular structures, also the basal cisterns can be opened before working in the tumor making the brain more lax.(13,19) The major disadvantages of this approach include a narrow working angle and long distance to the opposite side of the tumor. Also the upper part of the tumor is a blind area and significant brain retraction is needed to visualize it. In our study we do not use the pterional approach due to the previously mentioned disadvantages and we tried to be as basal as possible to devascularise the tumor early in the procedure and debulk the tumor then with retraction on the tumor capsule we are able to open the carotid cistern and visualize the neurovascular structures bilaterally. In big tumors more than 4 cm we routinely used lumbar drain to evacuate CSF after elevation of the bone flap. We use head rotation 15 degrees to the contralateral side to see the epsilateral carotid and optic and do the same thing on the opposite side benefiting from the bilateral exposure in the bifrontal approach.

Extensive skull base approaches with bilateral or unilateral orbital osteotomy are proposed to give shorter distance to the tumor and minimize brain retraction.(3,8) These approaches are time consuming during opening and reconstruction and are associated with increased risk of CSF leakage and we can avoid retraction by being flush with the orbital roof and we can also drill the inner aspect of the superior orbital rim and any bulge of the orbital roof for better exposure.

The percentage of total tumor resection in other series ranged from 50 to 100%.(3,5,6,30) The percentage of total removal is improving with the advent of modern microsurgical techniques reaching up to 100% in most of the recent series.(22,27) Subtotal removal is usually associated with bony infiltration and paranssal sinuses invasion.(22,27) In our study we used the high speed drill to remove the hyperostotic or infiltrated bone and we opened the infiltrated paranasal sinus from above to remove the tumor with good reconstruction which is best allowed with the bifrontal approach used in this study.

Post operative morbidity and mortality are improving in recent series due to the use of microsurgical techniques. The main causes of morbidity include CSF leake, meningitis, postoperative hematoma, subdural hygroma, worsening of vision, motor deficit and seizures.(3,5,22,27) In this study there was no mortality and we have 3 cases of CSF rhinorrhea, one case of unilateral worsening of vision, 3 cases of wound infection and 5 cases of seizures.

The recurrence rate for OGMs ranges from 0 to 41% in the literatures in macro and microsurgical procedures with a follow up period of 3.7 to 25 years.(22,27) Surgical series of short duration follow up show no recurrence. Series with longer periods of follow up (10-20years) show higher rates of recurrence.(22,27) In this study we have only one recurrence after total removal and this may be attributed to the relatively short follow up period (6 months to 8 years with a mean of 2.6 years).

Conclusion

Bifrontal approach is a simple, safe, and wide approach for OGMs. Lumber CSF drainage after elevation of the bone flap over- comes the non visualization of the basal cisterns early in the approach. It allows bilateral exposure for the tumor and the neurovascular structures. Reconstruction of the cranial base is ideal through this approach which minimizes the risk of CSF leak.

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