Anatomical Approach to Giant Pituitary Tumors




Introduction


Various classifications of pituitary tumors have been proposed on the basis of size, radiographic appearance, cytogenesis, staining properties, and endocrine function. There is no consensus regarding the terminology to be used in describing “giant” pituitary tumors. Large or giant tumors have been described as invasive adenoma, malignant adenoma, and carcinoma. Hardy classified pituitary tumors on the basis of their biological behavior. Some authors refer to pituitary tumors with size in excess of 30 mm, or those extending less than 6 mm from the foramen of Monro as “giant” irrespective of their invasiveness. Jefferson observed an incidence of giant pituitary tumors in about 6% of all cases. The histological characteristics of giant pituitary tumors do not usually correlate well with their gross features and generally consist of benign cells.


We classified those pituitary tumors, which measured more than 40 mm in maximum diameter, as being “giant. ” These tumors constituted 13.7 % of the total number of pituitary tumors seen during the period. The relatively larger percentage of giant pituitary tumors in our series could be related to ignorance of early symptoms due to the high rate of illiteracy and poverty, and difficulty in obtaining specialized medical help in our country.


Giant and “invasive” pituitary tumors are among the more complex neurosurgical challenges. Despite their histological benign nature, some of these tumors grow into a massive size and invade diverse anatomical structures. Due to the invasiveness and size of such tumors, surgical resection is difficult and on occasion dangerous. The results of radiation therapy are inconsistent.


The diagnosis of the pituitary tumor can usually be made on the clinical features and their classical anatomical extensions seen on imaging. Biopsy of the lesion thus usually has no relevance. The clinical outcome following a successful small or partial resection is generally not satisfactory. Radical resection of the tumor is the most optimum modality of treatment, although it is difficult and in itself dangerous. An exact understanding of the anatomical nature of the tumor and of its extensions is mandatory for planning and execution of surgery. A successful radical resection of the tumor can lead to rapid symptomatic recovery and an excellent long-term clinical outcome. The recurrence rate of the tumor after its radical resection is reported to be low. We had recently discussed our experience with giant pituitary tumors and had presented our surgical policy regarding these patients.


For this presentation, the authors have analyzed a series of 180 cases of giant pituitary tumors encountered during a 10-year period ( Figures 26-1 through 26-25 ). Giant nonfunctioning pituitary tumors are frequently soft in consistency, are slow growing, and therefore considering the massive size they have relatively innocuous presenting symptoms. It was observed that the giant pituitary tumors had a specific and anatomic pattern of extension, a feature that had great relevance in deciding the surgical strategy. The tumors were divided into four grades depending on the relationship to the diaphragma sellae and the cavernous sinus. Patients operated upon earlier and having a giant tumor mass were not included because it was observed that the extensions in some tumors was bizarre and did not follow a defined pattern seen in the nonoperated cases ( Figure 26-6 ).




Figure 26-1


A, T1-weighted coronal MR image showing a grade I giant pituitary adenoma. The cavernous sinuses are not invaded by the tumor. B, T2-weighted coronal MR image showing a predominantly hypointense tumor with some areas of hyperintensities. C, Contrast enhanced T1-weighted sagittal MR image showing some enhancement at the superior pole of the tumor.



Figure 26-2


A, T1-weighted MR image showing a grade 1 giant pituitary tumor. The tumor does not invade into the cavernous sinus. The hypointense region within the superior pole of the tumor is suggestive of tumor necrosis. B, Axial image of T2-weighted MR image demonstrating the giant size of the tumor, which appears in the form of two distinct lobulations. C, T1-weighted MR image showing a grade 1 giant pituitary adenoma. The tumor extends upto the level of the corpus callosum. The diaphragma sellae is intact despite the huge size of the tumor.



Figure 26-3


A, Contrast enhanced sagittal T1-weighted MR image showing a grade 1 giant pituitary tumor. B, Contrast enhanced coronal T1-weighted MR image showing the tumor. C, Postoperative scan showing the tumor resection. D, Postoperative sagittal image.



Figure 26-4


A, Sagittal T1-weighted MR image showing the grade 1 giant pituitary tumor. The superior aspect of the tumor is showing necrotic areas. B, Coronal image showing that the cavernous sinuses are not involved. C, Postoperative scan showing the resection of the tumor.



Figure 26-5


A, T1-weighted MR image showing the grade 1 pituitary tumor. The tumor has a subfrontal extension, which is covered by the diaphragma sellae. A transsphenoidal approach is ideal in such case. B, Coronal image showing that the cavernous sinuses are not involved. C, Postoperative scan showing the resection of the tumor.



Figure 26-6


A, Preoperative T1-weighted MR coronal image showing the tumor. Despite the growth, the diaphragma sellae is not transgressed. The cavernous sinuses are not involved. B, Sagittal image showing the tumor. C, Postoperative sagittal image showing the tumor resection by a transsphenoidal route. D, Coronal image showing the tumor resection.



Figure 26-7


A, Sagittal T1-weighted MR image showing the grade 1 pituitary tumor. The anterior elevation is the elevation at the level of planum sphenoidale. B, Coronal images showing the tumor. The diaphragma sellae is not transgressed. C, Postoperative sagittal scan showing tumor resection by the transsphenoidal route. D, Coronal image showing the tumor resection.



Figure 26-8


A, T1-weighted sagittal image showing the large tumor with areas of hyperintensities, suggestive of presence of organized blood. B, T2-weighted image showing the grade 1 giant tumor. The cavernous sinuses are not involved. The tumor is of a mixed intensity, with areas of hypointensity suggestive of organized blood clot. C, Postoperative scan shows resection of the tumor by a transsphenoidal route. D, Postoperative coronal image.



Figure 26-9


A, Preoperative T1-weighted scan showing the grade 1 giant pituitary tumor. B, Preoperative T2-weighted scan showing that the cavernous sinuses are not involved. C, Postoperative scan showing the tumor resection by a transsphenoidal route. The part of the tumor in the superior and anterior region has been left behind.



Figure 26-10


A, Sagittal T1-weighted MR image showing the grade 1 tumor. The diaphragma sellae is in the form of multiple nodules, but is intact and not transgressed by the tumor. B, Coronal image showing the grade 1 tumor. The cavernous sinuses are not involved.



Figure 26-11


A, Sagittal T1-weighted MR image showing the grade 1 tumor. The clival bone is involved by the tumor. B, Coronal T1-weighted MR image showing the tumor. The cavernous sinuses are displaced by the tumor.



Figure 26-12


A, Coronal T1-weighted MR image showing a grade 2 giant pituitary tumor. The cavernous sinus is involved by the tumor and the internal carotid artery is encased by the tumor. B, T1-weighted axial scan showing the tumor and the involvement of the cavernous sinus.



Figure 26-13


A, Axial T1-weighted MR image showing the involvement of the cavernous sinus by the tumor and encasement of the internal carotid artery. B, Coronal image showing the tumor involving the cavernous sinuses. C, Sagittal image showing the tumor.



Figure 26-14


A, Coronal T2-weighted MR image showing that both the cavernous sinuses are involved by the tumor. B, Axial T2-weighted MR image showing the involvement of both cavernous sinuses.



Figure 26-15


A, T1-weighted MR image showing the grade 2 pituitary tumor. B, T2-weighted image showing the involvement of the cavernous sinus. C, T2-weighted MR image showing the resection of the tumor. D, T1-weighted MR image showing residual tumor within the cavernous sinus.



Figure 26-16


A, T2-weighted MR image showing the grade 3 tumor involving the cavernous sinus and an elevation of its roof. B, Axial image showing the involvement of the cavernous sinus.



Figure 26-17


Contrast enhanced CT image showing the tumor and the involvement of the cavernous sinus. The roof of the cavernous sinus is elevated.



Figure 26-18


A, Contrast enhanced scan showing elevation of the roofs of both cavernous sinuses and a relatively small elevation of the diaphragma sellae. B, Axial image showing the tumor in the roofs of both the cavernous sinuses.



Figure 26-19


A, Coronal image of T2-weighted MR showing the grade 3 pituitary tumor. The tumor has elevated the diaphragma sellae and has involved the cavernous sinus. The roof of the cavernous sinus is elevated by the tumor. B, Sagittal image showing the tumor under the diaphragma sellae. C, Postoperative scan showing resection of the part of the tumor underneath the diaphragma sellae. D, Postoperative T2-weigthed coronal image showing the residual tumor in the cavernous sinus and under its superior dural wall.



Figure 26-20


A, Coronal T2-weigthed MR image showing the grade 3 pituitary tumor. Cavernous sinus is involved by the tumor and its roof is elevated. B, Postoperative scan showing the resection of the part of the tumor underneath the diaphragma sellae. The part of the tumor in the cavernous sinus is left behind.



Figure 26-21


A, T1-weighted sagittal image showing the tumor. B, Coronal image showing the grade 3 tumor, involvement of the cavernous sinus, and elevation of its roof. C, Axial image showing two blobs of a tumor: one underneath the diaphragma sellae and the other underneath the roof of the cavernous sinus.



Figure 26-22


A, Coronal image of the T1-weighted MR image showing a trifoliate pattern of the grade 3 tumor. The tumor has elevated the roofs of both the cavernous sinuses and also the diaphragma sellae. B, T2-weighted MR image showing the trifoliate pattern. C, Sagittal image showing the elevation of the diaphragma sellae.



Figure 26-23


A, Contrast enhanced MR image showing the grade 3 pituitary tumor. The tumor has involved both the cavernous sinuses and has elevated its roofs. B, Postoperative and postradiotherapy scan.



Figure 26-24


A, Coronal image showing the grade 4 tumor and the encasement of the two anterior cerebral arteries. B, T2-weighted image showing the encasement of the entire anterior circulation complex.



Figure 26-25


A, Axial T1-weigthed MR image showing the grade 4 pituitary tumor with encasement of the arteries in the region of anterior communicating artery complex. B, Image showing encasement of the anterior cerebral arteries.




Grade I Pituitary Tumors ( Figures 26-1 through 26-11 )


The general growth pattern of a pituitary tumor is that after the origin from the pituitary gland, the tumor grows in size and expands within the confines of the sella, which is enlarged and ballooned. The diaphragma sellae is elevated superiorly as the tumor grows in size. Grade I pituitary tumors were those that remained underneath the superiorly elevated diaphragma sellae and did not invade into the cavernous sinus. This group of tumors was confined underneath the elevated diaphragma sellae and laterally was bordered by an intact medial wall of the cavernous sinus. It was observed that the diaphragma sellae had a great degree of resilience and elasticity and transgression of this anatomic membrane was a relatively rare feature of the giant pituitary tumors. It bulged superiorly with the growth of the tumor and on occasion extended up to or even beyond the corpus callosum. The elevation of the diaphragma sellae was not always rounded or smooth, but was sometimes irregular and nodular. The diaphragma sellae was markedly thinned out at places and frequently formed big or small daughter balloons. The rounded superior wall of the tumor and the fact that no blood vessels are identified within the confines of the tumor were suggestive of the fact that the diaphragma sellae was intact. The presence of an intact diaphragma sellae was confirmed during surgery and this feature had surgical relevance because it formed an important protective barrier and such tumors could be resected radically through a relatively small exposure by a transsphenoidal route. The elevation of the diaphragma sellae even extended into the frontal or the temporal brain and in the retrosellar region.


Extension of the tumor into the sphenoid or other paranasal air sinus by transgressing the sellar dura was a relatively rare feature despite the massive tumor sizes seen in the series. In a large proportion of cases, the sellar dura remained intact despite the massive ballooning of the sella. We observed that a thinned out sellar bone was also preserved in most of these cases.


Surgical strategy: Transsphenoidal surgery was effective and relatively safe in grade I pituitary tumors. The surgical strategy was to expose the sellar part of the tumor and debulk the tumor mass. As the tumor mass was debulked, the suprasellar component progressively fell into the operative field. The Valsalva maneuver was used during surgery to facilitate the descent of the tumor mass. Wherever there was difficulty in exposure of the dome of the tumor mass, additional bone in the region of the tuberculum and planum sphenoidale were removed and the dural incision was extended. The understanding of the anatomical fact that the tumors did not transgress the diaphragma sellae, or extended into the supradiaphragmatic space, or encase the small and large blood vessels of the circle of Willis was crucial. Tumor resection is assisted by the pulsatile force of the diaphragma sellae and the diaphragma sellae should bulge in to the sella at the end of the tumor resection. It is necessary to visualize the entire diaphragma sellae at the end of the surgery, as otherwise small or large portions of the tumor can be missed within its folds. The tumor in patients with marked visual deficit is usually under significant pressure and “pours” into the surgical field after the sellar dural incision is made. The soft and necrotic nature of the tumor and the frequently encountered cystic areas within the confines of the tumor are positive features during tumor resection. Many of the tumors are highly vascular and will bleed excessively during the surgery. It is crucial at this stage to continue with the tumor resection and once the entire tumor is resected, hemostasis is relatively easily achieved. Hemostatic agents such as Gelfoam and Surgicel assist in the hemostasis. The author does not believe that cauterization is necessary within the confines of the tumor. If the diaphragma sellae is lacerated during the surgery and cerebrospinal fluid emerges into the surgical field, the Valsalva maneuver becomes ineffective. In such cases, reconstruction with a fat graft obtained from the thigh is mandatory. The sella and the sphenoid air sinus are packed with fat. It is generally better to overpack the region than to underpack it. This is because the fat in the region is vascularized early and chances of infection or rejection are extremely low. On the other hand, a cerebrospinal fluid fistula can be a formidable and life-threatening problem. The author also uses bone pieces and vascularized mucosal flap to strengthen the reconstruction.


None of the patients with grade I pituitary tumors have needed a transcranial operation in the authors’ series during the last 5 years.


The authors use a sublabial-interseptal approach to the sella. Such an approach was found to be versatile in general and particularly in cases with giant pituitary tumors. It provided a quick and wide exposure to the region. The approach avoided the need to work in a relatively small nasal cavity and to make a mucosal incision through hair follicles. Although theoretically, an endoscope can help in identifying a tumor in hidden corners, I have not found this tool extremely effective or even necessary while dealing with giant pituitary tumors.

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Jun 10, 2019 | Posted by in NEUROLOGY | Comments Off on Anatomical Approach to Giant Pituitary Tumors
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