4.4          Case Study – Pituitary adenoma

Adenomas are the commonest primary neoplasms of the pituitary gland.  They are benign and slow growing.  Those smaller than 10mm in diameter are termed microadenomas and those larger than 10mm are termed macroadenomas.  Approximately 75% of patients with pituitary adenomas will have symptoms of hormone excess, while the remaining non-functioning tumours, usually the macroadenomas, present with clinical symptoms related to tumour mass-effect (e.g. headache, visual field defects, cranial nerve palsies (Evanson, 2001).

On high resolution CT scans pituitary adenomas are typically hypodense in comparison with the normal gland on both contrast-enhanced and unenhanced images.  Similarly, on MRI 80-90% of microadenomas appear as focal hypointense lesions compared with the normal gland on unenhanced T1-weighted images.    After Gd-DTPA injection the adenoma is seen to enhance less brightly than the rest of the pituitary gland.  The use of Gd-DTPA increases the sensitivity of MRI in adenoma detection.  Although up to 50% of microadenomas are hyperintense on T2-weighted images, overall, T2-weighted sequences are less sensitive than T1-weighted sequences for the detection of pituitary adenomas.  For this reason they are not used routinely MRI of the pituitary (Evanson, 2001; Rao and Robles, 1999) 

Other evidence of adenoma includes: focal erosion of the sella floor or focal convexity of the superior surface of the gland.  Tilting of the pituitary stalk may also indicate the presence of an adenoma.  Macroadenomas have similar characteristics to microadenomas and can be reliably and accurately identified by CT.

Large solid pituitary macroadenomas appear as masses that are nearly isointense with the brain in both T1 and T2-weighted images and they enhance moderately with Gd-DTPA.  Cystic, necrotic and haemorrhagic components within the tumour have intermediate signal intensity intermediate between that of CSF and that of tumour in T1-weighted images and have high signal intensity in T2-weighted images.  Macroadenomas may grow upwards to compress the optic nerves and chiasma or may extend downward to the sphenoid sinus, which are best appreciated on coronal MR images.  It may also encroach on the suprasellar cistern and may displace the optic chiasm or temporal lobe.  It is important to diagnose cavernous sinus invasion by pituitary adenoma but unfortunately neither CT nor MRI has proved highly accurate in preoperative detection.  The identification of tumour lying laterally to the lateral tangent the intra and supracavernous internal carotid artery on coronal MR images is highly suggestive of cavernous sinus involvement.  Sagittal MR images are especially useful in demonstrating chiasmal compression and posterior extension of the tumour (Evanson, 2001; Rao and Robles, 1999) 

Large pituitary adenomas are prone to develop infarction or haemorrhage owing to their tenuous blood supply.  Pituitary tumours may also undergo ischemic necrosis if blood supply to tumour is impaired which may lead to pituitary apoplexy, which can be only identified at surgery or during MRI (Rao and Robles, 1999)

4.5.1 Patient

This 62-year-old lady presented with the following features:

·        a non-specific headache,

·        decreased visual acuity in both eyes

·        normal pupillary light reaction

·        bitemporal superior quandrantopia (i.e. absence or loss of one quarter of the visual field)  

The patient had a CT scan immediately performed.  A mass in the sellar region was identified by the radiologist however, the results were not specific.  The patient was referred for an MRI scan as follows.

Figure 11 Coronal T2-weighted 3mm cut through pituitary

Figure 12 Coronal T1-weighted 3mm cut through pituitary

4.5.2        Materials and methods

The same materials and methods were used a stated in section 3.5.2

4.5.3        Protocols and pulse sequence parameters

Table 4 Pulse sequences in pituitary MRI

The above protocol is similar to the one suggested by Bradley (1999).  In his recommended protocol the axial PD/T2 FSE is not included.  Our center performs this sequence as a general brain check-up for any pathologies.  FSE is used in this case because it is a fast sequence.  As regards Gd-DTPA administration, the patient was administered a half dose, as this proved effective in pituitary imaging.  The coronal post-contrast sequence was run first as the contrast will diffuse from the normally enhancing gland.  3D FSPGRE has been used to image the pituitary, however, magnetic susceptibility effects from air in the sphenoid sinus often degraded image quality.   Dynamic studies have been also attempted, as recommended in section 4.4.4.1 with T1 FSE however; I have seen no particular difference in the resulting images.

The protocol utilised by the Massachusetts General Hospital (2002) appears quite different to our protocol.  We agree in using sagittal and coronal T1-weighted images pre and post contrast.  They also recommend the use of axial T2 and FLAIR, axial DWI through the whole brain and MRS if possible.  The use of fat saturation through the sella in the post contrast images sequences is recommended.  As an optional sequence they recommend the use of a T1 axial through the whole brain.

4.5.4 Results

On scanning the patient with the above parameters, the radiologist identified a homogenous contrasting tumour measuring 1.5cm, which is abutting the optic chiasma.  No other focal lesion was identified.  The tumour is intra-sellar extending to the supra-sellar region.  The tumour is invading the hypothalamus and causing a dilatation in the left ventricle.  The tumour is encasing the middle cerebral artery.  The tumour probably corresponds to a pituitary macro adenoma.

4.5.5 Evaluation of the examination

The images achieved (figs 11-14) are of good quality.  The patient was co-operative throughout the examination.  The only problem with pituitary examination is scan time due to number of pulse sequences, contrast usage and moreover, in our center we use SE which are long sequences. 

The macroadenoma enhanced after contrast administration.  Nevertheless, areas within the tumour appear less intense than other parts.  On discussing this fact with a radiologist, the outcome was that there could be areas of haemorrhage or necrosis within such a large tumour.

Figure 13 Sagittal T1-weighted 3mm section (post gadolinium)

Figure 14 Coronal T1-weighted 3mm section (post gadolinium)

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