By EbtsamA.Abdelbary Imaging of Pituitary Tumours
The pituitary gland (or hypophysiscerebri), together with its connections to the hypothalamus,acts as the main endocrine interface between the central nervous system and the rest of the body. Gross anatomy The pituitary gland sits at top of the base of the skull in a concavity within the sphenoid bone called the sellaturcica (pituitary fossa), immediately below the hypothalamus and optic chiasm. The pituitary is usually divided into anterior and posterior parts; Anterior pituitary Posterior pituitary(neurohypophysis)
Relations The pituitary, located within the pituitary fossa, It has complex relations. • Inferiorly • sphenoid bone (basisphenoid) • sphenoid sinus • Superiorly • diaphragmasellae and hypophyseal cistern • suprasellar cistern • pituitary stalk • optic chiasm • circle of Willis • hypothalamus • Laterally • cavernous sinuses (and its contents) • Anteriorly • anterior intercavernous sinus • anterior clinoid processes • Posteriorly • posterior intercavernous sinus • dorsum sellae
Pituitary tumours • Pituitary tumours, are tumours which arise from the pituitary gland itself, include: • Pituitary adenoma • pituitary microadenoma • pituitary macroadenoma • Pituitary carcinoma • Pituicytoma • Pituitary metastases • Spindle cell oncocytoma (rare)
Pituitary adenomas • Pituitary adenomas are primary tumours that occur in the pituitary gland and are one of the most common intracranial neoplasms. • Depending on their size they are broadly classified into: • Pituitary microadenoma: less than 10 mm in size • Pituitary macroadenoma: greater than 10 mm in size
Pituitary microadenomas • Pituitary microadenomas are a minority of all pituitary adenomas, but has imaging and management challenges on account of their size and clinical presentations. • By definition, a microadenoma is less than 10 mm in size. If the same tumour is greater than 10 mm in size, it is then considered a pituitary macroadenoma. • Differences in presentation and imaging merely represent a difference in size rather than any fundamental difference in biology.
Radiographic features CT Although CT was able to detect up to 80-90% of microadenomasbetween 5-10 mm in size, it was highly technique and radiologist dependent, and had difficulty in identifying smaller nodules
MRI • MRI is the mainstay of imaging for pituitary microadenomas, and required dedicated pituitary sequences (thin slice, small field of view, dynamic contrast acquisition). Contrast-enhanced MRIs have a sensitivity of 90%. • Post contrast and especially thin section dynamic contrast-enhanced imaging is an important part of a pituitary MRI and has significantly improved diagnostic accuracy. • Some often subtle morphology changes can be identified on non-contrast images, however. These include bulkiness of the gland on the side of the microadenoma, subtle remodeling of the floor of the sella, deviation of the pituitary infundibulum away from the adenoma. • T1: usually isointense to normal pituitary • T1 C+ (Gd) • dynamic sequences demonstrate a rounded region of delayed enhancement compared to the rest of the gland • delayed images are variable, ranging from hypo-enhancement (most common) to isointense to the rest of the gland, to hyperintense (retained contrast) • T2: variable, but often a little hyperintense.
A rounded hypoenhancing lesion measuring 8 X 6 X 6.5 mm centered within the right aspect of the pituitary gland.No compression of the optic chiasm, infundibulum remains deviated to the left and no evidence of invasion of the cavernous sinus.
Pituitary macroadenomas • Pituitary macroadenomasare the most common suprasellar mass in adults, and responsible for the majority of trans-sphenoidalhypophysectomies. They are defined as pituitary adenomas greater than 10 mm in size and are approximately twice as common as pituitary microadenomas.
Radiographic features • Pituitary macroadenomas are by definition >10 mm diameter masses arising from the pituitary gland, and usually extending superiorly. Bilateral indentation at the diaphragmasellae can give a snowman or figure eight configuration.
Sagittal T1W image +C demonstrating intentation of the diaphragm sellae that gives a snowman or figure 8 configuration to the macroadenoma.
CT • Adenomas which are solid, without haemorrhage, typically have attenuation similar to the brain (30-40 HU), Non-contrast attenuation can vary depending on haemorrhagic, cystic and necrotic components. After contrast administration, it demonstrates moderate contrast enhancement; less marked than one typically seen in meningiomas. Calcification is rare.
MRI • MRI is the preferred imaging modality, not only able to delineate the mass, but also clearly visualise the optic chiasm, anterior cerebral vessels and cavernous sinuses. • Overall signal characteristics can significantly vary depending on tumour components such as haemorrhage, cystic transformation or necrosis. • T1 • typically isointense to grey matter • larger lesions are often heterogeneous and vary in signal due to areas of cystic change/necrosis/haemorrhage • T1 C+ (Gd) • solid components demonstrate moderate to bright enhancement • T2 • typically isointense to grey matter • larger lesions are often heterogeneous and vary in signal due to areas of cystic change/necrosis/haemorrhage • GRE/SWI • most sensitive for detecting any haemorrhagic components, which appear as areas of signal loss N.B: calcification is rare but should be excluded by reviewing CT scans • Assessment of cavernous sinus invasion can be difficult. The most convenient method is to assess the degree of encasement of the cavernous portion of the internal carotid artery.
MRI of the pituitary demonstrating a large mass extending into the suprasellar cistern and compressing the optic chiasm. Note the invasion into the left cavernous sinus with encasement of the ICA.