Optic chiasm
Fiona Rowe in Visual Fields via the Visual Pathway, 2016
The pituitary gland lies in a bony cavity of the sphenoid bone; the sella turcica. The roof of the sella (the diaphragma sellae) is formed by a fold of dura mater which stretches from the anterior clinoids to the posterior clinoids. The optic nerves and the optic chiasm lie above the diaphragma and are therefore susceptible to suprasellar extension of a pituitary tumour (Figure 7.5). Tumours that remain confined to the sella will not cause visual field defects. Within the optic chiasm, the inferonasal retinal nerve fibres cross low and anteriorly and therefore are most vulnerable to damage from expanding pituitary lesions. In about 80% of normal subjects, the optic chiasm lies directly above the sella (Bergland et al. 1968). In approximately 10% of normal subjects, the optic chiasm is situated more anteriorly, over the tuberculum sellae (prefixed). Another anatomical variation present in the remaining 10% of cases is a postfixed optic chiasm where the chiasm is located more posteriorly over the dorsum sellae. The optic nerves thus have a long intracranial course and as a result pituitary tumours are more likely to present with compression of the optic nerves.
Pituitary surgery
Michael Y. Wang, Andrea L. Strayer, Odette A. Harris, Cathy M. Rosenberg, Praveen V. Mummaneni in Handbook of Neurosurgery, Neurology, and Spinal Medicine for Nurses and Advanced Practice Health Professionals, 2017
The nasal cavity provides access to this space, because the sphenoid bone connects it to the pituitary gland above. The carotid arteries are in close relationship to the sphenoid bone, creating an impression in the lateral wall of the sphenoid sinus. Also, both cavernous sinuses lie laterally to the sphenoid bone. The pituitary gland rests in the center of the bone, the sella turcica, limited anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae. The sphenoid sinus is an air cavity inside the sphenoid body. It separates the cavernous sinuses, the cavernous segments of the carotid arteries, the optic, extraocular, and trigeminal nerves, and the pituitary gland from the nasal cavity (Figure 37.4). The sella turcica is separated from the rest of the brain by the diaphragma sellae, a membrane that covers the pituitary gland, except for a small opening in its center for the pituitary stalk.
Craniopharyngioma
David A. Walker, Giorgio Perilongo, Roger E. Taylor, Ian F. Pollack in Brain and Spinal Tumors of Childhood, 2020
Although most craniopharyngiomas of childhood arise in the region of the tuber cinereum, a small percentage originates from more caudal craniopharyngeal duct cell rests within the sella turcica.118 As these tumors grow, the diaphragma sellae stretches over the dorsal aspect, separating it from suprasellar structures and preventing tumor adherence to the optic apparatus, hypothalamus, and vessels of the circle of Willis. This feature of the pathological anatomy allows a radical removal of solid intrasellar tumors and large infradiaphragmatic cystic tumors (Puget grade 0 and 1), through a transsphenoidal/transnasal approach.110,114,118,119 In centers with appropriate clinical experience and a coordinated ear, nose, and throat–pediatric neurosurgical team, endoscopic endonasal and extended endonasal approaches achieve a high rate of resection of not only sellar, but some suprasellar, tumors.120–122 In pediatric craniopharyngiomas, up to 80% of the tumors may be amenable to transsphenoidal/transnasal resection.100,102,119
Arachnoid prolapse in endoscopic transsphenoidal surgery of pituitary adenoma, technical note
Published in British Journal of Neurosurgery, 2023
Guive Sharifi, Nader Akbari Dilmaghani, Seyed Mousa Sadrhosseini, Shima Arastou
Prolapse of the suprasellar cistern arachnoid into the sellar fossa rapidly occurs after removal of a large cystic or soft tumor during transsphenoidal surgery. According to the flaccid diaphragma sellae theory, ‘suprasellar extension from large sellar tumors or any pathology that could cause pressure on the diaphragm sellae leading to produce a long flaccid diaphragm resulted from a decrease of its thickness strength and increase its length that could easily be prolapsed due to CSF pressure and drag the adhered structures by itself’ [1]. However, it has been mentioned that prolapse of the suprasellar cistern toward the sellar floor may require some type of reconstruction [12]. Acute dropping of the elongated optic nerves and chiasm into the sellae may also be present; however, severe postoperative visual deterioration is rarely found in this situation [13]. Previously, we used some maneuvers to decrease intra cranial pressure such as hyperventilation or the administration of a lumbar drain or other similar apparatus to reduce intracranial pressure, so prolapsed arachnoid get smaller then reconstruct sellar ploor. However, these are costly maneuvers which are expensive and not so effective. Therefore, we have used a simple method-cauterization of the arachnoid, which significantly reduces the size of the prolapsed arachnoid with upward movement into the intrasellar space through the sellar floor defect.
Post-operative vision loss: analysis of 587 patients undergoing endoscopic surgery for pituitary macroadenoma
Published in British Journal of Neurosurgery, 2022
John W. Rutland, Jonathan T. Dullea, Eric K. Oermann, Rui Feng, Dillan F. Villavisanis, Shivee Gilja, William Shuman, Travis Lander, Satish Govindaraj, Alfred M. C. Iloreta, James Chelnis, Kalmon Post, Joshua B. Bederson, Raj K. Shrivastava
Six patients presented with a primary pituitary adenoma, and five had received previous surgical resection at an outside institution. Grafts were used for 10 patients during surgical reconstruction. Graft materials included abdominal fat (45.5%), fascia lata (27.3%), and a combination of abdominal fat and fascia lata (18.2%). The diaphragma sellae was opened in nine out of the 11 surgeries. A preventative graft was placed in one patient without diaphragma opening due to interoperative identification of thinning of the diaphragma. All 11 tumours were subtotally resected with an average resection rate of 87.4%. Four patients had a hematoma and six patients had pneumocephalus identified on post-operative imaging. The average systolic blood pressure measured in the post-anaesthesia care unit was 141.5 ± 18.2 mm Hg. Seven patients returned to the operating room within 24 h of initial surgery. The average time to return to the operating room was 33.5 ± 40.5 h. Surgical factors are shown in Table 2.
The snowman sign in a patient with pituitary tumor apoplexy
Published in Journal of Community Hospital Internal Medicine Perspectives, 2021
Khulood Bukhari, Vandhna Sharma, Sonia Gupta, Abbas Motazedi
Pituitary macroadenomas are the most common suprasellar masses in adults and account for about 10% of all intracranial neoplasms. They are slow-growing and may expand the bony sella and extend superiorly into the suprasellar cistern to compress the optic chiasm. Their classic appearance on neuroimaging is a snowman-like or ‘figure of 8’ configuration as a result of bilateral indentation of the tumor by the rigid dura of the diaphragma sellae. Meningiomas arising from the sellar diaphragm may resemble pituitary neoplasms but can be seen separate from the pituitary gland. Other differentials for suprasellar masses include craniopharyngiomas and aneurysms of the parasellar internal carotid artery [1].
Related Knowledge Centers
- Cerebrospinal Fluid
- Endoscopic Endonasal Surgery
- Pituitary Stalk
- Pituitary Gland
- Sella Turcica
- Hypothalamus
- Dorsum Sellae
- Tuberculum Sellae
- Middle Clinoid Process
- Pituitary Adenoma