Pituicytoma is not a common term but usually meant to describe a rare tumor of the posterior lobe that is composed of large foamy cells. These are rarely identified during life, and most often incidental findings at autopsy.. The word is often misused to decribe a pituitary adenoma.
These tumors arise from pituicytes, which are stromal (supporting) cells of the posterior lobe. They may present with visual field defects, or by asymptomatic during life and discovered only at autopsy or on MRIs done for other purposes. They usually don't show diabetes insipidus in spite of their location. Surgery seems to be the preferred mode of therapy but as they are so rare, it is difficult to say there is any "definitive" treatment. They tend to be more vascular than standard pituitary adenomas arising from the anterior lobe of the gland, which may make surgery more difficult or tedious. Overall only about 35 or so of these tumors are in medical literature, which gives an idea of their rarity.