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Neuroradiology Case of the Week

Case 150

Alisa Johnson, Sudhir Kathuria MD, Ravinder Sidhu MD,
and PL Westesson MD, DDS, PhD

Clinical Presentation: The patient is a 42-year-old female presenting with headaches and increased prolactin levels. The present MR examination is requested to evaluate for any pituitary mass lesion.

Radiological Findings: There is a cystic rounded mass in craniocaudal dimensions showing bright signal on T2, and low signal on T1-weighted images. In the dynamic images, this lesion is not enhancing, with no enhancement seen after post-contrast images. The pituitary stalk is slightly deviated towards the right side. The optic chiasm appear unremarkable, with no mass effect on them.

Differential Diagnosis: 

• Non-neoplastic cyst (Rathke cleft or pars intermedia)
• Craniopharyngioma
• Pituitary hyperplasia

Diagnosis: Cystic Pituitary Microadenoma

Clinical Discussion: Pituitary adenomas are the most common tumor of the pituitary in adults. There are microadenomas (<10mm) and macroadenomas (>10%), together they represent 10-15% of intracranial tumors. Microadenomas are more common and tend to present earlier because they are generally hormonally active. Where as the macroadenomas will present later with symptoms caused primarily by the mass effect of the macroadenoma.
     Microadenomas can produce a variety of hormones but are usually asymptomatic. If patients are symptomatic they can present in a variety of ways including amenorrhea or galactorrhea indicating a prolactinoma, giganism/acromegaly indicates a growth hormone producing tumor, infertility and menstrual abnormalities indicated a gonadotropin producing tumors, and hyperthyroidism indicates a thyrotropin producing tumors. Prolactinomas usually present in patients between 20-35 years of age and between 30-50 year olds for growth hormone producing microadenomas. Prolactinomas are usually treated with bromocriptine or cabergoline. If the patient is symptomatic due to secretion of a hormone other than prolactin, surgical resection will be considered [1].

Neuroimaging Discussion: Most imaging of the pituitary gland is done with MRI.; CT is only used when MRI is contra-indicated. Studies indicate a detection rate of 80% with CT but in practical work, CT is far inferior to MRI and should only be used when MRI is clearly contra-indicated. On non-contrast CT, pituitary adenomas are isodense. When contrast is administered, 2/3 appear hyodense to normal pituitary on dynamic scans. MRI has a detection rate of 85% which is increased to 95-100% with dynamic MRI studies [2]. Dynamic studies are done after a bolus of contrast with thin (3mm) slices in coronal projection every 30 seconds. Dynamic studies are helpful because the best diagnostic clue for pituitary adenomas is an intrapituitary lesion that enhances less rapidly than surrounding normal gland. 10-30% of pituitary microadenomas can only be seen on dynamic scans [3]. If hemorrhage and necrosis are present then the T1WI will have variable signal intensity from isointense to hyperintense. T1WI with contrast will show a hypointense mass 70-90% of the time in the pituitary because the adenoma will enhance more slowly than the normal pituitary tissue [2]. T2WI typically shows pituitary adenomas as isointense to normal pituitary gland. T2WI with contrast will show hypointense mass in the pituitary 70-90% of the time [3].

References:

1. Klachko DM. Pituitary microadenomas. http://www.emedicine.com/med/topic2973.htm, May 23, 2005.
2. Castillo M. The Core Curriculum: Neuroradiology. Lippincott Williams & Wilkins, Philadelphia: 2002.
3. Osborn AG. Diagnostic Imaging: Brain, 1st ed. Amirsys Inc: Altona, 2004