Normal thyroid seen microscopically consists of follicles lined by a an epithelium and filled with colloid. The follicles vary somewhat in size. The interstitium, which may contain "C" cells, is not prominent.

Normal thyroid follicles appear at the lower right. The follicular adenoma is at the center to upper left. This adenoma is a well- differentiated neoplasm because it closely resemble normal tissue. The follicles of the adenoma contain colloid, but there is greater variability in size than normal.

At the center and to the right is a medullary carcinoma of thyroid. At the far right is pink hyaline material with the appearance of amyloid. These neoplasms are derived from the thyroid "C" cells and, therefore, have neuroendocrine features such as secretion of calcitonin.

The circumscribed mass lesion present here in the sella turcica is a pituitary adenoma. Though pituitary adenomas are benign, they can produce problems either from a mass effect (usually visual problems from pressing on the optic chiasm and/or headaches) or from production of hormones such as prolactin or ACTH.

The microscopic appearance of the pituitary adenoma is shown here. Note the monotonous appearance of these small round cells.

An islet cell adenoma is seen here, separated from the pancreas by a thin collagenous capsule. A few normal islets are seen in the pancreas at the right for comparison.

The normal histologic appearance of prostate glands and surrounding fibromuscular stroma is shown here at high magnification. A small pink concretion (typical of the corpora amylacea seen in benign prostatic glands) appears in the gland just to the left of center. Note the well-differentiated glands with tall columnar epithelial lining cells. These cells do not have prominent nucleoli.

At the right are normal prostatic glands containing scattered corpora amylacea. At the left is prostatic adenocarcinoma. Note how the glands of the carcinoma are small and crowded. Prostatic adenocarcinomas are given a histologic grade (Gleason's grading system is used most often, and includes a score of 1 to 5 for the most prominent component added to a score of 1 to 5 for the next most common pattern). For example, this adenocarcinoma could be given a Gleason grade of 3/3.