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1. IMAGING OF SELLA AND PARASELLAR LESIONS

2. ANATOMY OF SELLA The sella turcica ("Turkish saddle") is a midline concavity in the basisphenoid of the central skull base that contains the pituitary gland. The sella is entirely embedded within the sphenoid bone. The anterior borders of the sella are formed by the tuberculum sellae and anterior clinoid processes of the lesser sphenoid wing, whereas the posterior border is formed by the dorsum sellae. The top of the dorsum sellae expands slightly posteriorly and laterally to form the posterior clinoid processes, which in turn form the upper margin of the clivus The sellar floor is part of the sphenoid sinus roof, which is partially or completely aerated. The cavernous segments of the internal carotid arteries lie in shallow bony grooves (the carotid sulci) located inferolateral to the pituitary fossa

3. MENINGES COVERING THE SELLA The meninges in and around the sella form important anatomic landmarks. Dura covers the bony floor of the sella , separating it from the pituitary gland. A thin dural reflection borders the pituitary fossa laterally and forms the medial cavernous sinus wall. A small circular dural shelf, the diaphragma sellae forms a roof over the sella that almost covers the pituitarygland . The diaphragma sellae has a variably sized central opening, the diaphragmatic hiatus, that transmits the pituitary stalk

4. A prominent basal arachnoid membrane, called the Liliequist membrane, forms trabeculae that cross the suprasellar cistern and cover the hypothalamus and diaphragma sellae. A sleeve of arachnoid reflects over the pituitary stalk, forming a thin hypophyseal cistern that can provide a surgical dissection plane in approaching suprasellar masses.

5. CONTENTS : PITUATORY GLAND The pituitary gland, also called the hypophysis with two distinct parts (sometimes called "lobes"): the anterior pituitary, also called the adenohypophysis (AH), and the posterior pituitary or neurohypophysis (NH) (25-40). The anterior and posterior pituitary lobes differ in embryologic origin, structure, and function but are joined together into a single gland, the hypophysis. Anterior Pituitary Gland (Adenohypophysis). The AH, formerly called the anterior lobe, accounts for 75-80% of the total pituitary gland volume. The AH wraps anterolaterally around the NH in a U-shaped configuration. The AH is subdivided into three parts: the pars distalis (pars anterior), pars intermedia, and pars tuberalis .

6. The AH develops as an outgrowth—called Rathke pouch—of embryonic ectoderm that lines the roof of the buccal cavity .This outgrowth subsequently detaches from the buccal cavity, and its anterior wall thickens to become the largest part of the AH called the pars distalis. The posterior wall differentiates into the pars intermedia, whereas the dorsolateral portions extend around the infundibulum as the pars tuberalis .

7. Pituitary gland signal intensity varies. With the exception of neonates (in whom the AH can be large and very hyperintense), the AH is typically isointense compared with cortex on both T1- and T2WI. The NH usually has T1 shortening (the so-called posterior pituitary "bright spot") caused by the presence of neurosecretory granules. The posterior pituitary "bright spot" does not contain lipid and does not suppress on fat-suppression techniques . The infundibular stalk is isointense with the pituitary except for a central hyperintensity on T2WI. The pituitary gland does not have a blood-brain barrier, so it enhances rapidly and intensely following contrast administration.

8. Pituitary gland enhancement is slightly less intense than that of venous blood in the adjacent cavernous sinuses. The infundibular stalk and tuber cinereum of the hypothalamus also lack a blood-brain barrier and enhance on T1 C+. Physiologic hypertrophy is seen during puberty and young menstruating female patients is common, with normal gland height reaching 10 mm.

9. Pregnant and postpartum lactating female patients have even larger, superiorly convex pituitary glands that may measure up to 12-14 mm in height. The infundibular stalk measures approximately 3-4 mm in diameter at the level of the optic chiasm and gradually tapers to about 2 mm as it descends to its insertion into the pituitary

10. HYPOTHALAMUS AND THIRD VENTRICLE The hypothalamus lies directly above the pituitary gland, extending posteriorly from the lamina terminalis (anterior wallof the third ventricle) to the mammillary bodies. The tuber cinereum is part of the hypothalamus. It is the thin convex mass of gray matter that lies between the optic chiasm anteriorly and the mammillary bodies posteriorly. The infundibular stalk extends inferiorly from the tuber cinereum,gradually tapering as it descends to become continuous with the posterior pituitary lobe.

11. The third ventricle lies in the midline just above the hypothalamus Two CSF-filled recesses of the third ventricle,the optic and infundibular recesses, project inferiorly toward the hypothalamus. The optic recess is more rounded and lies just in front of the optic chiasm. The infundibular recess is more conical and pointed, extending into the upper part ofthe pituitary stalk

12. CAVERNOUS SINUS AND CONTENTS The cavernous sinuses (CSs) are irregularly shaped, trabeculated venous compartments that lie along the lateral aspects of the sella turcica. The CSs are contained within a prominent lateral and a thin (often inapparent) medial dural wall. Important CS contents include the cavernous ICA segments and several cranial nerves The abducens cranial nerve (CN VI) is the only cranial nerve that actually lies within the CS, inferolateral to the cavernous ICA. Cranial nerves III, IV, V₁, and V₂ all lie within the lateral dural wall .

13. The oculomotor nerve (CN III) is the most cephalad of the cavernous cranial nerves and is contained within a thin sleeve of CSF-filled arachnoid called the oculomotor cistern. The trochlear nerve (CN IV) lies just inferior to CN III. Two divisions of the trigeminal nerve (CN V), the ophthalmic (V₁) and maxillary (V₂) divisions, lie inferior to the trochlear nerve. The mandibular nerve (CN V₃) does not enter the CS. The trigeminal ganglion lies within another arachnoid -lined CSF space, Meckel cave. CN V₃ exits inferiorly from the trigeminal ( gasserian or semilunar ) ganglion and passes through the foramen ovale into the masticator space

14. APPROACH TO SELLAR LESIONS

15. MICROADENOMA P ituitary microadenomas are less than 10 mm in diameter and are located in the pituitary gland . On T1 – hypointense and on T2 – slightly hyperintense lesion . Unless they hemorrhage, small microadenomas may be inapparent on standard nonenhanced sequences.Sensitivity being 70% Many microadenomas appear slightly hypointense on T1 C+ . Others enhance more strongly and may become isointense with the enhancing pituitary gland, rendering them virtually invisible. Microadenomas enhance more slowly than the normal pituitary tissue. Fast image acquisition during contrast administration can often discriminate between the slowly enhancing microadenoma and rapidly enhancing normalgland .

16. MACROADENOMA P ituitary macroadenomas are adenomas over 10mm in size . Macroadenomas are red-brown, lobulated masses that often bulge upward through the opening of diaphragma sella or, less commonly, extend laterally toward the cavernous sinus. Approximately half of macroadenomas contain cysts , necrosis and/or hemorrhagic foci as they grow bigger. Pituitary adenomas are almost all WHO grade I tumors.

17. As they grow, they first expand the sella turcica and then grow upwards and there can be a suprasellar extension with elevation and compression of the optic chiasm, can extend laterally into the cavernous sinus( if there is more than 50% encirclement of the carotid artery, meningiomas tend to constrict the carotid artery, macroadenomas do not. ) Because they are soft tumors, they usually indent at the diaphragma sellae, giving them a 'snowman' configuration. This is one feature that can help distinguish between a pituitary macroadenoma and a meningioma . Another feature which can help differentiate them is enlargement of the sella turcica - this generally only occurs with pituitary macroadenomas that originate in the sella .

18. Another feature being the diaphragmmatic leaflets are displaced upwards by this macroadenoma which started in the sella and is growing upwards. A lesion originating above the sella and growing downwards would push the leaflets in the other direction ( meningiomas

19. IMAGING A sellar or combined intra- and suprasellar mass that cannot be identified separately from the pituitary gland—the mass is the gland—is the most characteristic imaging finding . CT Findings: Bone CT may show an enlarged, remodeled sella turcica. The lamina dura of the sellar floor is generally intact. “Giant" pituitary adenomas may erode and extensively invade the skull base, mimicking metastasis or aggressive infection . Pituitary adenomas demonstrate variable attenuation on NECT scans. Macroadenomas are usually isodense with gray matter, but cysts (15-20%) and hemorrhage (10%) are common. Calcification is rare (less than 2%). Moderate but heterogeneous enhancement of macroadenomas is typical on CECT , but small microadenomas may be invisible.

20. MR IMAGING Macroadenomas are usually isointense with cortex . The posterior pituitary "bright spot" is absent (20%) or displaced into the supradiaphragmatic cistern(80%) on T1-weighted sagittal scans. Small cysts and hemorrhagic foci are common. Adenomas are generally isointense with gray matter on T2WI but can also demonstrate heterogeneous signal intensity. Hyperintensity along the optic pathways on T2/FLAIR occurs in 15-20% of cases in which macroadenomas compress the optic chiasm. Hemorrhagic adenomas "bloom" on T2*. Most macroadenomas enhance strongly but heterogeneously on T1 C+ . CTA in patients with suprasellar extension of macroadenoma may show the supraclinoid internal carotid and anterior choroidal arteries displaced laterally

21. DD’s Pituitary hyperplasia (know patient age, gender) Physiologic (young/pregnant/lactating female patients) Nonphysiologic (end-organ failure). Imaging : Symmetric increase in pituitary gland size and overall volume without focal mass effect or bony erosion is the classic finding. MR demonstrates an enlarged gland that bulges upward and may even contact the optic chiasm. The enlarged pituitary is isointense with cortex on both T1- and T2WI Other tumors Meningioma, craniopharyngioma, metastasis Pituitary carcinoma is very rare . Craniospinal mets and systemic spread can confirm the diagnosis. Nonneoplastic lesions Aneurysm – flow void on mri . Hypophysitis

22. MENINGIOMA Meningiomas  are  extra-axial tumours  and represent the most common  tumor of the meninges . They are a non- glial neoplasm that originates from the meningocytes or arachnoid cap cells of the  meninges  and are located anywhere meninges are found. Meningioma of the diaphragma sellae can usually be identified as clearly separate from the pituitary gland below.

23. Imaging : On non-contrast CT 60% slightly hyperdense to normal brain, the rest are more isodense . On post-contrast CT 72% brightly and homogeneously contrast enhance   . Hyperostosis  typical for meningiomas that abut the base of the skull On T1 usually isointense to grey matter. T1 C+ ( Gd ):  usually intense and homogeneous enhancement On T2 usually isointense to grey matter

24. ANEURYSM Abnormal dilatation of the vessel.The abnormal dilatation of the cavernous segment of the ICA causes mass effect on the stalk of the pituatory and causes inhibition of dopamine which leads to hyperprolactinemia or galactorrhea (stalk section effect) On CT we see a slightly hyperattenuating lesion. On MRI : Predominantly dark on MRI . (Air , fat, blood are dark on mri )

25. CRANIOPHARANGIOMA Craniopharyngioma (CP) is a benign, often partly cystic sellar /suprasellar mass that probably arises from epithelial remnants of Rathke pouch. These are benign tumors, they have thick walls and are locally invasive. Loaction : CPs are primarily suprasellar tumors (75%). A small intrasellar component is present in 20-25% of cases. Occasionally, CPs (especially the papillary type) arise mostly or entirely within the third ventricle.

26. IMAGING A partially calcified, mixed solid and cystic extraaxial suprasellar mass in a child is the classic appearance. A compressed, displaced pituitary gland can sometimes be identified as separate from the mass. CT Findings: Adamantinomatous CPs follow a "rule of ninety," i.e., 90% are mixed cystic/solid 90% are calcified and 90% enhance .

27. CT Shows hypodense mass involving all the three cranial fossa with focus of calcification .

28. Papillary CPs rarely calcify. They are often solid or mostly solid. When they contain intratumoral cysts, the cysts are usually smaller and less complex appearing than those seen with adamantinomatous CPs. MR Findings: Signal intensity varies with cyst contents . Multiple cysts are common, and intracystic fluid within each cyst varies from hypo- to hyperintense compared with brain on T1WI

29. CP cysts are variably hyperintense on T2WI and FLAIR. The solid nodule is often calcified and moderately hypointense . The cyst walls and solid nodules typically enhance following contrast administration MRS shows a large lipid-lactate peak, characteristic of the cholesterol and lipid constituents of a CP. pMR shows low rCBV (25-60).

30. Enhancing nodule at the corner differentiates this from rathkes cleft cyst.Shows thin rim of enhancement .

31. INTRASELLAR LESION Common • Pituitary hyperplasia (physiologic, pathologic) • Pituitary microadenoma • Empty sella COMMON SUPRASELLAR MASSES : Adults • Pituitary adenoma (mass = gland) • Meningioma (mass separate from gland) • Aneurysm ("flow void," pulsation artifact) Children Craniopharyngioma (90% cystic, 90% calcify, 90% enhance) Hypothalamic/optic chiasm astrocytoma (solid, no calcification).

32. WHEN THE MASS CANNOT BE SEPARATED FROM THE PITUITARY GLAND Common • Pituitary macroadenoma • Pituitary hyperplasia (physiologic, pathologic ). LESS COMMON SUPRASELLAR MASSES Rathke cleft cyst (well delineated, separate from pituitary) Arachnoid cyst (behaves just like CSF) Dermoid cyst (looks like fat , so bright on T1.)

33. RATHKE’S CLEFT CYST Rathke cleft cyst (RCC) is a benign endodermal cyst of the sellar region. Arise from remnants of the fetal Rathke pouch. When the embryonic stomodeum (the primitive oral cavity) invaginates and extends dorsally, it forms the endoderm-lined craniopharyngeal duct.

34. IMAGING : CT and MRI NECT scans show a well-delineated round or ovoid mass within or just above the sella turcica . Threequarters of RCCs are hypodense on NECT, whereas 20% are mixed hypo- and isodense . Between 5 and 10% are hyperdense . Calcification is uncommon compared with craniopharyngioma . MR Findings: Signal intensity varies with cyst contents. Half of all RCCs are hypointense on T1WI, and half are hyperintense

35. The majority of RCCs are hyperintense on T2WI whereas 25-30% are iso - to hypointense . Intracystic nodule in 40-75% of cases.Nodule represent desquamted cellular debris. RCCs are almost always hyperintense on FLAIR . An enhancing rim ("claw" sign) of compressed pituitary gland can often be seen surrounding the nonenhancing cyst .

36. Saggital T 1+c shows enhancing rim of compressed pituatory surrounding the non enhancing cyst.

37. DD’s : Craniopharyngioma . Floccular , rim, or nodular calcifications are common in craniopharyngioma , whereas RCCs rarely calcify. The rim or nodular enhancement in craniopharyngioma is generally thicker and more irregular than the "claw" of enhancing pituitary gland that surrounds the nonenhancing RCC.

38. HYPOTHALAMIC HAMARTOMA Hypothalamic hamartoma (HH), also known as diencephalic or tuber cinereum hamartoma , is a nonneoplastic congenital malformation associated with precocious puberty, behavioral disturbances, and gelastic seizures. The majority of HHs are located in the tuber cinereum , i.e., between the infundibular stalk in front and the mammillary bodies behind. Age :1-3 years , M > F.They can be pedunculated or sessile. Pedunculated lesions extend inferiorly from the hypothalamus into the suprasellar cistern, whereas sessile HHs project from the floor of the third ventricle into its lumen.

39. HHs are well-defined round or ovoid soft tissue masses that resemble normal brain parenchyma. Histologically , HHs consist of well-differentiated small and large neurons interspersed with variable amounts of glial cells. Sagittal image shows a pedunculated hypothalamic hamartoma interposed between the infundibulum anteriorly and the mammillary bodies posteriorly .

40. IMAGING General Features : A nonenhancing hypothalamic mass between the infundibular stalk and mammillary bodies is the classic imaging appearance of HH . CT Findings: NECT scan shows a homogeneous suprasellar mass that is isodense to slightly hypodense compared with brain. Intralesional cysts may be present in larger HHs. HHs do not enhance on CECT.

41. MR IMAGING Pedunculated HHs are shaped like a collar button on sagittal , extending inferiorly into the suprasellar cistern. Signal intensity is usually isointense to normal gray matter on T1WI and iso - to slightly hyperintenseon T2/FLAIR . HHs do not enhance following contrast administration . MRS shows mildly decreased NAA and slightly increased choline , consistent with reduced neuronal density and relative gliosis ( cell membrane marker). Myoinositol is elevated , which is consistent with an increased glial component compared with normal brain

42. Hamartoma between infundibular stalk and mamillary bodies.

43. GERMINOMA A germinoma is the most common intracranial germ cell tumor. Germinomas are located in the pineal region most commonly (50-65%) and the suprasellar region in approximately 25-35% of cases. Germinomas of the suprasellar region most commonly present with diabetes insipidus . Less common presenting signs include visual loss and hypothalamic-pituitary dysfunction with decreased growth and precocious puberty

44. Germinomas of the suprasellar region are classically hyperdense on CT, similar to lymphoma. When involving the pituitary axis, a germinoma involves the infundibulum and/or neurohypophysis and often presents in a child with an absent posterior pituitary "bright spot" . Diffuse enhancement of an enlarged infundibulum is the typical MR appearance. Diffusion restriction on DWI is typical . These lesions crawl along the floor of the 3rd ventricle.

45. CHORDOMA Chordomas are the most common lesions of the clivus , also a favored location for metastases and chondrosarcomas . Large, fungating mass positioned at the level of the clivus . The CT shows some calcifications in this area. Chordomas tend to occur in the midline

46. ARACHANOID CYST

47. EPIDERMOID CYST

48. NORMAL VARIANTS

49. EMPTY SELLA An empty sella (ES) is an arachnoid -lined, CSF-filled protrusion that extends from the suprasellar cistern through the diaphragma sellae into the sella turcica . Rarely completely "empty"; a small remnant of flattened pituitary gland is almost always present at the bottom of the bony sella . An ES can be primary secondary.

50. A primary empty sella occurs when an unusually wide (sometimes called "incompetent") opening in the diaphragma sellae allows intrasellar herniation of arachnoid and CSF from the suprasellar cistern above into the sella turcica below. A secondary empty sella occurs when pituitary volume is reduced with surgery, bromocriptine therapy, or radiation treatment. A rare but important cause of secondary ES is Sheehan syndrome. It results from ischemic pituitary necrosis due to severe postpartum hemorrhage. The great majority of patients with Sheehan syndrome have an empty sella on CT or MR scan

51. Most patients with ES are asymptomatic or have nonspecific symptoms such as headache and in some present as mild endocrine disturbances. Patients with idiopathic intracranial hypertension commonly have an associated partially empty sella . Occasionally, patients present with visual disturbances caused by inferior displacement of the optic chiasm into the ES. It has an association with IIH.When there is an increased intracranial pressure , there is hernaition of arachnoid space through deficient diaphragm

52. IMAGING FEATURES Imaging studies show intrasellar CSF with a thinned pituitary gland flattened against the sellar floor. CT Findings: CSF-density fluid fills a sella that may be of normal size or moderately enlarged. The bony floor of the sella is intact in primary ES, but, in secondary ES, it often shows a surgical defect caused by transsphenoidal hypophysectomy . The infundibular stalk and pituitary remnant enhance normally on CECT scans.

53. The intrasellar fluid behaves exactly like CSF on T1- and T2WI and suppresses completely on FLAIR. DWI shows no diffusion restriction . The major differential diagnosis of an ES is a suprasellar arachnoid cyst that may herniate into the sella turcica . The bony sella is often not simply enlarged but eroded and flattened. Arachnoid cysts follow CSF signal intensity on all MR sequences and completely suppress on FLAIR images .

54. PITUATORY APOPLEXY Etiology • Hemorrhagic or nonhemorrhagic pituitary necrosis • Preexisting macroadenoma (65-90%) Clinical Issues • Sudden onset • Headache, visual defects • Hypopituitarism (80%) • Can be life-threatening because of adrenal crisis and leading to shock. • Can result in permanent pituitary insufficiency • Sheehan syndrome = postpartum pituitary necrosis

55. Imaging • Enlarged pituitary with or without Hemorrhage (85-90%) • Rim enhancement around nonenhancing gland. The major differential diagnosis of PAP is hemorrhagic macroadenoma . Focal hemorrhages in adenomas are common, but, in contrast to PAP, the clinical course is typically subacute or chronic. Most adenomas enhance strongly but heterogeneously, whereas PAP demonstrates rim enhancement around a predominantly nonenhancing , expanded pituitary gland .

56. TO BE REPORTED Most surgical approaches ( transethmoid , transnasal , or transseptal ) pass through the sphenoid sinus to reach the sella . Regardless of which operative technique—microscopic or endoscopic—is used, delineating sphenoid sinus anatomy is important. Four key features of sphenoid sinus anatomy should be identified: the location and extent of pneumatization , the sellar configuration, any septation and the intercarotid distance.

57. Pneumatization : classified as sellar (57%), postsellar (22%), presellar (21%), or conchal (2%).

58. The rare conchal nonpneumatized sphenoid is important to recognize preoperatively, as it makes transsphenoidal surgery more difficult. highly pneumatized sphenoid sinus may make the surgery technically easier but also distorts the anatomic configuration, attenuating the bone and potentially uncovering the carotid arteries and optic nerves. A pneumatized dorsum sellae can be penetrated during surgery, resulting in a CSF leak. Sellar Configuration : The presence (well defined) or absence (ill defined) of sellar bulging in relation to the sellar floor and the degree of sphenoid pneumatization .

59. well- pneumatized sphenoid sinus with a prominent sellar bulge facilitates surgery, which is further eased if the sellar floor is thinned or disrupted by tumor. Septation : The presence or absence of an intersphenoid septum should be determined. The intersphenoid septum must be removed to expose the sellar floor, so determining its location is crucial. Intercarotid Distance :The intercarotid distance is measured between the medial aspects of the two signal "voids" of the cavernous ICA segments as seen on midsellar coronal MR.

60. Intercarotid distance varies widely, ranging from 10-12 mm to 30 mm (mean of 23 mm). Narrow distances (< 12 mm) increase the chance of vascular injury during transsphenoidal surgery. The cavernous internal carotid arteries (ICAs) normally lie lateral to the pituitary gland in the parasellar carotid sulci . Occasionally, the ICAs are positioned medially and actually course inside the bony sella . These "kissing" carotid arteries may compress the pituitary gland, squeezing it upward and making it appear modestly enlarged.

61. The presence of medially positioned ICAs is highly important in presurgical planning for transsphenoidal hypophysectomy , as normally positioned ICAs are not encountered in this approach

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