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Neuroradiology Case of the Week

Case 81

Deepa Popuri, Leena Ketonen, MD, PhD

Clinical Presentation: A 64-year-old female with pituitary tumor. Evaluation of the tumor mass is requested.

Radiological Findings:  MRI examination demonstrates a mass in the pituitary fossa consistent with diagnosis of pituitary macroadenoma. This mass measures 2.4 cm craniocaudally, 1.8 cm in AP, and 2.3 cm in transverse dimensions. It shows enhancement with Gadolinium administration and has a somewhat heterogeneous high-signal intensity on T2 weighted images and isointense to brain on FLAIR and T1 weighted images. The mass is also approximately 50% abutting the surface of the right internal carotid artery. There is no abutment or encasement of the left internal carotid artery.

Diagnosis: Pituitary macroadenoma

Discussion: 
CLINICAL DISCUSSION:

Epidemiology: Pituitary masses make up approximately 10% of all intracranial neoplasms and nearly half of all sellar and juxtasellar masses. Macroadenomas are found twice as often as microadenomas in imaging studies. These masses are more often found in adults, with less than 10% of pituitary neoplasms occurring in children. They occur four to fives more often in females than males [1].

Presentation: Most pituitary adenomas are clinically silent [1]. Three-fourths of all symptomatic cases are due to excessive hormonal secretion. The remaining one-quarter of cases show symptoms of tumoral mass effect including headache, cranial nerve palsy, and cerebrospinal fluid rhinorrhea [2]. Larger tumors may result in displacement of the optic chiasm and visual field defects [3]. Hemorrhage, headache, vomiting, opthalmoplegia, or visual loss may occur [2].

Classification: Pituitary neoplasms are classified according to size and hormonal activity. Microadenomas are masses <10 mm and macroadenomas are masses >10 mm. Types of hormone secreting adenomas include the following:

1. Prolactin cell adenoma results in excessive prolactin secretion
2. Growth hormone secreting adenoma may result in gigantism or acromegaly.
3. Corticotroph adenoma may result in Cushing’s disease.
4. Silent corticotroph adenoma presents asymptomatically.
5. Gonadotroph adenoma results in secretion of fragments of follicle stimulating hormone and leutinizing hormone.
6. Thyrotroph adenoma results in secretion of the thyroid stimulating hormone (TSH) as well as alpha subunit of TSH.
7. Plurihormonal adenoma results in secretion of TSH, growth hormone, and prolactin.
8. Null cell adenoma or oncocytoma results in secretion of nonfunctioning hormonal fragments. Patients with null cell adenoma are often asymptomatic despite presence of macroadenoma [1].

Pathology: Infarction and hemorrhage are possible in macroadenoma due to tenuous blood supply [2]. Most pituitary adenomas are benign and slow growing [1]. Metastases to the brain, liver, lymph node, or lung are possible but quite rare. Invasion into the cavernous sinus is a poor prognostic sign, as it indicates tumor aggressiveness and predicts a more difficult surgical resection. Tumor may block drainage of interstitial fluid through Virchow-Robin spaces to the subarachnoid space. Distention of Virchow-Robin spaces may result to fluid retention that appears as edematous change along the optic tract [4].

Treatment: Management of asymptomatic patients with pituitary adenoma is under controversy. The sphenoid sinus may become blocked, resulting in the accumulation of various secretions. Surgical intervention in this situation involves craniotomy. Another surgical approach is transphenoidal resection with reconstruction of the sellar floor [1,2]. Early decompression of optic nerve is associated with improved prognosis [3]. Gadolinium enhanced imaging provides useful presurgical information as to location and size of the adenoma. Recurrence rates after resection are 16% after eight years and 35% after 20 years [1,2]. Post-surgical findings may be obscured for 3-4 months due to swelling and inflammation [2]. Bromocriptine therapy is useful in treatment of hyperprolactinemia associated with pituitary microadenoma. Reduction in tumor size can be expected within one week of therapy. MR imaging is useful in monitoring responsiveness to therapy or development of hemorrhage, cyst, or necrosis [1,2].

NEUROIMAGING DISCUSSION:
     Macroadenoma: It is important to exclude cavernous sinus invasion, as this is a poor prognostic sign. Invasion may be excluded if the normal pituitary gland appears compressed between the tumor and cavernous sinus. If invasion occurs, the tumor appears encase in the internal carotid artery. Uncomplicated macroadenoma is isodense to the pituitary gland on CT and isointense to gray matter on MR images. Macroadenomas are more variable in appearance on NECT and MR images due to necrosis, hemorrhage, or cyst. Complicated cases will appear heterogeneous and demonstrate patches of intense enhancement. Cavernous invasion is possible with superior bulging of the masses through the diaphragm sellae into the supersellar cistern [2]. Sagittal and coronal T1WI may reveal upward growth of tumor and compression of the optic chiasm. Degree of compression is correlated to severity of visual impairment [3,5]. Arita reports a case in which extension of macroadenoma led to encasement of both optic nerves and disturbance of vessels supplying the pathways [5]. Edematous changes may appear as high-signal along the optic tract on coronal and axial T2-weighted images. These are not present in all cases and are not correlated with visual defects [4].
     Microadenoma: Two-thirds of microadenomas appear hypodense and one-third show early enhancement on CT. Most appear hypointense on T1-weighted images and approximately one-half are hyperintense on T2 images. Gadolinium contrast improves sensitivity and specificity for microadenoma as much as 10% [1]. Following IV Gadolinium contrast injection in a dynamic MR study, the gland shows early enhancement and the microadenoma stays as a nonenhancing area. Later the gland clears and the microadenoma enhances.

References:

1. Osborn A. Diagnostic Neuroradiology. St. Louis: CV Mosby, 1994.
2. Elster, Allen D. Modern imaging of the pituitary. Radiology 1993; 187:1-14.
3. Ikeda H, Yoshimoto T. Visual disturbances in patients with pituitary adenoma. Acta Neurologica Scandinavica 1995; 92:157-160.
4. Saeki, Naokatsu, Uchin Yoshio, Murai Hisayuki et al. MR imaging study of edema-like change along the optic tract in patients with pituitary region tumors. AJNR 2003;24:336-342.
5. Arita K, Uozumi T, Yano T, et al. MRI visualization of complete bilateral optin nerve involvement by pituitary adeonoma: a case report. Neuroradiology 1993; 35:549-550.