Pituitary Region Mass With Intrinsic High T1 Signal

Pituitary region mass with intrinsic high T1 signal are relatively frequently encountered, and the presence of high T1 signal narrows the differential somewhat. The differential includes:

• pituitary macroadenoma with haemorrhage / necrosis

Pituitary macrocadenomas are the most common suprasellar mass in adults, and responsible for the majority of transsphenoidal hypophysectomies. They are defined a as pituitary adenomas greater than 10mm in size and are approximately twice as common as pituitary microadenomas ¹⁰.

For a general discussion, including epidemiology, please refer to the article on pituitary adenomas.

Clinical presentation

Patients typically present with symptoms of local mass effect on adjacent structures (especially optic chiasm). Some may present hormal imbalance, with symptoms of hypopituitarism (from compression) or secretion. Hormonal imbalance due to overproduction tends to present earlier and tumours are thus usually small at presentation. This mode of presentation is discussed in the article on pituitary microadenomas.
Rarely pituitary apolplexy may present acutely and often catastrophically.

Optic chiasm compression

The optic chiasm is located directly over the pituitary gland in 80% of individuals. The rest are divided between pre and post fixed chiasms. A prefixed optic chiasm is located anterior to its normal position over the tuberculum sellae, whereas a postfixed chiasm is located over the dorsum sellae ¹⁰.
A macroadenoma growing superiorly out of the pituitary fossa (of for that matter other pituitary region masses) will contact, elevate and compress the central part of the chiasm in most individuals. This central part carries fibers from the nasal retina, and thus results in the classical bitemporal hemianopia ¹⁰. Patients typically complain of bumping into things or having car accidents, but as the macular fibres are often spared, they may not be aware of actual visual deficits.
In cases of prefixed or postfixed chiasms, or when the macroadenoma grows asymmetrically then the optic nerves or optic tracts can be compressed, resulting in a variety of visual deficits.

Cavernous sinus invasion

Some macroadenomas demonstrate invasive growth, and extension into the cavernous sinuses is characteristic. Prolactin secreting tumours are most frequently responsible for cavernous sinus extension, and typically prolactin level increase significantly when the tumour gains access to the sinus ¹⁰. Once in the sinus, tumour are difficult to completely resect.
They may compress cranial nerves resulting in deficits, although this is uncommon, seen in only 1 - 14% of cases ¹⁰. Occulomotor nerve (CN III) is most commonly involved, followed by the abducens nerve (CN VI) ¹⁰.

Pathology

Most macroadenomas are non secretory (endocrinologically inactive). They are a type of benign epithelial tumour composed of adenohypophysial cells

Radiographic features

Pituitary macroadenomas are by definition > 10mm mass arising from the pituitary gland, and usually extending superiorly. Indentation at the diaphragma sellae can give a snowman or figure eight configuration ¹⁰.

CT

No contrast attenuation can vary depending on haemorrhagic, cystic and necrotic components. Adenomas which are solid, without haemorrhage, typically have attenuation similar to brain (30-40HU) and demonstrates moderate contrast enhancement; less marked than one typically sees in meningiomas.
Calcification is rare.

MRI

MRI is the preferred imaging modality, not only able to exquisitely 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 ¹⁰
  • larger lesions are often heterogeneous and vary in signal due to areas of cystic change / necrosis / haemorrhage
• T1 C+ (Gd)
  • solid components demonstrates moderate to bright enhancement
• T2
  • typically isointense to grey matter ¹⁰
  • larger lesions are often heterogeneous and vary in signal due to areas of cystic change / necrosis / haemorrhage
• T2* gradiant echo
  • most sensitive for detecting any haemorrhagic components, which appear as areas of signal loss
  • 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. Less than 90 degrees makes involvement of the sinus very unlikely, where as greater than 270 degrees makes involvement almost certain