| BackgroundPituitary adenomas are benign tumors arising in adenohypophysial cell and approximately represent10-15%intracranial neoplasms, rank third following gliomas and meningiomas. Surgery remains the primary therapy of choice except for prolactinomas. Tumor recurrence after operation is the hardest problem of therapy for pituitary adenomas and seriously threaten to patients’ quality of life. There are many factors affecting tumor recurrence, include the size of the tumors, growth rate,the extent of resection,adjuvant therapy, etc. Among those factors, pituitary adenoma extention into surrounding structures, especially into cavernous sinus, are the principal cause which leading to tumor recurrence. Invasive pituitary adenoma was proposed by Jefferson in1940, which was defined as "the pituitary adenoma grows to break its envelope and to invade the adjacent structure such as the dura, the optic nerve, bone and so on". Scheithauer classified invasive pituitary adenomas as the interim type from benign pituitary adenomas to pituitary cancers. These three diseases can not be distinguished in pathology, but show differences in the biological behaviors, pituitary adenomas developed in expansive growth modes and covered by "pseudocapsule" which formed by compression the surrounding structure, invasive pituitary adenomas bring out aggressive growth pattern and invde the diaphragm sellae, bone, vascular vessel, but do not present characteristic of intracranial metastasis which pituitary cancers show. The concept and diagnostic criteria of invasive pituitary adenomas have considerable controversies that lead to the difficulty in diagnosis and treatment. Pathological examination, imaging technology, molecular biology test and operative observation were applied in the diagnosis of invasive pituitary adenomas, these methods provide different medical information, but could not produce a unified diagnostic criteria.Effects of sellar regional anatomy on growth pattern of pituiary adenomas have drawn the attentions of researchers in recent years. Sellar region is located near the center of the head and consist of the complex configure. The front, rear and bottom of hypophyseal fossa where pituitary gland sited are bony structure, the top and sides are the dura mater and all these structure could restrict the pituitary adenomas extension. In term of morphological study of sellar bone, Wang jian-xin have presented the anatomic features of sellar turcica and carotid sulcus and stated that lateral bone windows of sella turcica and carotid sulcus can affect to different degrees the growth pattern of pituitary. Wei quan-tang found that most of pituitary adenomas grow perpendicularly to pituitary fossa superior orifice and the slant angle of pituitary fossa superior orifice could determine the growth direction of pituitary adenoma toward suprasellar region. Studies on membrane surrounding the pituitary gland have been made for many years. Some researchers state that the there is no a dural wall existing between cavernous sinus and carotid artery, but a loose, fibrous tissue and the extension of pituitary tumors into the cavernous sinuses is not for aggressive growth, but for the absence of a strong separation. There are also some authors declare that the defects exist on the medial wall of cavernous sinus which leads to the expansion of pituitary adenomas into cavernous sinus. Recently, some researchers found through histological and micro-dissection method that the medial wall of cavernous sinus is a intact dural membrane and deduce that invasive adenomas might be a radiological misunderstanding of the extremely displacement of the medial wall by the tumor’s pushing, a membranous interface still exists between the tumor and the cavernous sinus.Sellar region anatomy application for explanation of pituitary adenoma growth modes provided a new way to investigate the reality of invasive pituitary adenomas and would helpful to diagnosis and treatments. The roof of hypophyseal fossa formed by diaphragm sellae and lateral wall by medial wall of cavernous sinus, which are the major obstacles to pituitary adenomas expansion. There were authors even thought that the cancellous bone of the sella turcica is less of a barrier against extension of tumor than the ligamentous attachments of the dural structures. This study was designed to research the anatomic features of dura mater enclosing the pituitary gland and its relationships with the growth pattern of pituitary adenomas was explored.Objective1、Observation and description of morphological features of diaphragm sellae, optic chiasm, pituitary stalk are about to make the anatomy of sellar region more systematic and detailed. The relations between diaphragm sellae and pituitary adenomas extension were explored.2、Histological and anatomic method were used to define the membrane composition of diaphragm sellae and medial wall of cavernous sinus; the position relationship of medial wall of cavernous sinus relative to cavernous segment of internal carotid artery were paid attention to explore its effect on growth pattern of pituitary adenoma.Material and method1. Microanatomy of diaphragm sellae, optic chiasm and pituitary stalkFifteen adult cadaveric head, the arteries of which were injected with red latex, were used to perform anatomic study. The cranial vault and brain tissue above sellar region were removed and optic nerve, optic tract were intently reserved. Under the surgical microscopy, the length of intracranial segment of optic nerve, the angle of optic chiasm were measured and position relationships of foramen diaphragm sellae relative to optic chiasms were noted. After optic nerve being cut in the intracranial opening of the optic canal, we backward fliped the optic nerve and optic chiasm, discontinued the pituitary stalk at the junction connected to the infundibulum. The anatomical data and morphological characteristic of pituitary stalk, diaphragm sellae and adjacent structure were measured and demonstrated.2. Microanatomy of diaphragm sellae and medial wall of cavernous sinusHeads from6fetal cadavers aged6to8months were studied. All specimens were infused with10%formalin solution into the umbilical to embalm all specimens. Tissue blocks of skull base (include sellar region, cavernous sinus, part of middle cranial fossa and petrous bone) were dealt with decalcification, dehydrating, embedding. Serial histological sections were obtained in sagittal and coronal direction. All these sections were stained with Masson’s triple and picrosirius-picric acid staining. Under the light microscopy, the course and distribution of the membranate structures were observed. Ten adult cadaveric head, the arteries of which were injected with red latex and the veins with blue latex, were used to perform anatomic study. Under the surgical microscope, membranous structure of sellar region were dissected step by step, their course and distribution of the membranate structures were described, the position relationships of cavernous segment of internal carotid artery and medial wall of cavernous sinus were remarked especially. Mean of the thickness of diphragma sellae and medial wall of cavernous sinus was compared with oneway ANOVA, and if P<0.05, for further multiple comparison with SNK method. The criterion for statistical significance for all tests was P<0.05, all tests used two-tailed test. All data processing were carried out in SPSS13.0statistical software.Result1. The length of intracranial segment of right optic nerve were12.36±1.71mm, and the left were12.20±1.86mm. Both sides of the optic nerve fibers converge to form the optic chiasm, which posteriorly continued with lamina terminalis, anterior commissure and lower part of the hypothalamus. The angle of optic chiasm were62.29±12.17°(range,49.20-87.20°). The midpoint of the optic chiasm passing through crista galli were located on the midline in66.7%(10cases) and to the left and right sides of the sella turcica in20%(3cases) and13.3%(2cases) respectively. The foramen diaphragm sellae (FDS) was completely covered by OC in73.4%(11cases), but it was partly seen superiorly in26.6%(4cases). The position of FDS relative to OC situated in the midline in66.7%(10cases), to the left part in26.7%(4cases) and right part in6.6%(1case).After the optic nerve and optic chiasm having been removed, a quadrilateral area were seen which formed by limbus sphenoidale, dorsum sellae, and anterior, posterior petroclinoid ligament. The diaphragma sellae attachs to the tuberculum sellae and dorsum sellae and forms the roof of the hypophyseal fossa. In the center, the diaphragm has an opening through which the infundibulum and inferior hypophyseal artery courses. The diaphragm sellae extends from the tuberculum sellae anteriorly to the dorsum sellae posteriorly. Laterally, it limits to the roof the cavernous sinus. There is no a clear boundary between diaphragm and the roof. The roof of cavernous sinus were divided by interclinoid ligament into anteromedial carotid triangle and posterolateral oculomotor triangle. Diaphragmatic fibers were concentrically around the foramen. Diaphragm sellae appeared concave in80%(12cases), convex in13.3%(2cases) and flat in6.7%(1case) when view from above. The foramen diaphragm sellae is round or oval and its diameter greatly varied. The average of anteroposterior distance of foramen diaphragm sellae was6.59±2.45mm (range,2.20-12.10mm) and the average lateral-to-lateral distance was7.32±2.60mm (range,3.10-13.40mm). we classified the diaphragm sellae into three types according to the foramen diaphragm sellae diameters variations, closed type, the diaphragmatic opening was less than5mm and the pituitary stalk was tightly surrounded in13.3%(2cases); normal type, the diaphragmatic foramen was5-10mm and the gap exist between stalk and diaphragma in73.4%(11cases); and open type, the diaphragmatic opening was more than10mm and the remnants of the diaphragma were seen around the upper part of the pituitary fossa in13.3%(2cases). The position relationship of pituitary stalk relative to the tuberculum and dorsum sellae can be classified3type, prefix typed, pituitary stalk sited in front of dorsum sellae in53.3%(8cases);middle type, in the middle part in40%(6cases) and postfix type, in the the back of tuberculum sellae in6.7%(1case).2. In all fetal skull base specimens, dura mater was found to divided into meningeal and periosteal layer over the tuberculum sellae and dorsum sellae. The meningeal layer covers the pituitary gland and folds downward around the foramen. Two meningeal layer formed diaphragm sellae on the top of hypophyseal fossa. Meningeal and periosteal layer mix together again in the bottom of sellar floor. In the meningeal layer and periosteal layers confluence, anterior intercavernous sinus, posterior intercavernous sinus and inferior intercavernous sinus were shaped. The dural fibers sent out from the periphery and the center of diaphragma fused to constitute the pituitary dural sac. The pituitary sac is a continuous dual pouch, its superior wall is strengthened by diaphragm sell, the anterior, posterior and inferior wall adhere to the periosteal layer, lateral wall is a screen which separated the cavernous sinus. The pituitary gland is founded to be packed by two membranous layer, the inner layer is lamina propria which tightly adheres to the gland and and some connective tissue penetrated the gland, the outer layer is the dural sac. A potential space between the2layers was found on the surface of the adenohypophysis. these2layers got closer and closer from the anterior lobe toward the posterior lobe of the gland and finally adhered on the surface of the neurohypophysis. Many fibrous trabeculae divided cavernous sinus into a lot of cavity, which adhere to the wall of cavernous sinus and neurovascular structure coursed in it. The medial wall of the cavernous sinus is a bilayered membrane, composed of the lateral part of the pituitary sac and the fibrous layer, which separated the pituitary gland from the cavernous sinus.The course and distribution of the membranous structures observed by adult cadaver head dissection are corresponded to the results obtained from histological study in the fetal skull base specimens. Thickness of membranes surrounding pituitary gland were statistically difference between four groups(F=53.412, P=0.000). The periphery of diaphragm sellae was significantly thicker than the center and the medial wall of cavernous sinus(P<0.05); the thickness of the upper third was statistically greater than the lower third(P<0.05).The medial wall of cavernous sinus are intact without perforations and defects although the weakness were founded in lower third than upper third of it. In8of the20cavernous sinus, the sellar part of the medial wall rested against the intracavernous carotid; in15%(3sides) the internal carotid arteries shifted from sulcus and partly squeezed into the hypophyseal fossa, that leaded to be partly coated by medial wall of cavernous sinus; in15%(3sides) the anterior lobe of pituitary gland extended towards one side of the cavernous sinus and closely contact the internal carotid artery, but away from another side; and in10%(2sides in the same specimens) there was a tongue-like lateral protrusion of the gland that extended around the cavernous segment of the intracavernous carotid.Conclusion1. Most of the foramen diaphragm sellae are completely covered by optic chiasm, but few are partly seen superiorly. The position of foramen diaphragm sellae relative to optic chiasm situated in the midline account for the majority, to the left and right part manifest minority. This positional relationship could be used to explain the visual symptoms of patients with pituitary tumors. Pituitary adenomas protrude from diaphragmatic foramen located in the midline of optic chiasm result in bitemporal hemianopsia, while in the side of the optic chiasm lead to left or right visual field defect.2. The diaphragm sellae could be classified into three types according to the diaphragmatic foramen diameters variations, closed type; normal type; and open type. The sizes of diaphragmatic opening could affect the growth direction of pituitary adenomas. If the opening was large, the resistance from the top was less than from others sides and the pituitary tumor was inclined to suprasellarly grow. While if the opening was small, the tumor was barriered by diaphragm sella and easily extended into the cavernous sinus, even broke through the bony structures into ethmoid and sphenoid sinus.3. The position of pituitary stalk could be categorized as3types:prefixed type, middle type, and postfixed type. Postfix and middle type accounted for the vast majority, only a small number of prefix type. This anatomic knowledge is helpful to identify and protect the pituitary stalk and neurohypophysis in the operations.4. The diaphragm sellae covers the hypophyseal fossa and formed by2meningeal layer. The dural fibers sent out from the periphery and the center of diaphragma fused to constitute the pituitary dural sac. The medial wall of the cavernous sinus is a bilayered membrane and the2layers of the medial wall are composed of the lateral part of the pituitary sac and the fibrous layer. The medial wall is intact without perforations and defects.5. The normal anterior lobe of pituitary gland might rest against the cavernous segment of internal carotid artery. In this anatomic conditions, the tumor could easily cross the carotid artery into the cavernous sinus and membranous layers such as lamina propria, the medial wall would exist between the tumor and the cavernous sinus, so that the tumor was not invasive growth.6. The diagnosis and treatment of invasive pituitary adenomas should based on endocrinology, pathology, imaging, and intraoperative findings, especially the influence of sellar regional anatomy on the growth pattern should be taken into considerations. |
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