Follicular thyroid adenoma

Follicular thyroid adenoma
Diagnosis in short
Follicular adenoma. H&E stain.
Synonyms	follicular adenoma
LM	cellular appearance (low magnification), microfollicles, thick fibrous capsule without invasion, negative for nuclear features of papillary thyroid carcinoma
LM DDx	thyroid gland nodular hyperplasia, follicular thyroid carcinoma, noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), Papillary thyroid carcinoma follicular variant
Gross	lesion with thick capsule
Site	thyroid gland
Signs	thyroid mass
Prevalence	uncommon
Prognosis	benign
Clin. DDx	follicular carcinoma, other thyroid tumours
Treatment	excision to exclude carcinoma

Follicular thyroid adenoma, abbreviated FTA, is a benign lesion of the thyroid gland.

General

• Most common neoplasm of thyroid.
• Encapusled lesion (surrounded by fibrous capsule).
• Cannot be diagnosed on thyroid FNA, as one cannot exclude invasion through the capsule without examining all of it.

Gross

• Thick capsule.

Notes:

• The entire capsule should be submitted.
  • A good start for most thyroid specimens with a thick capsule is 10 blocks.

Images

• 

  FTA. (WC/Euthman)

Microsopic

Features:

• Cellular.
• Thick capsule - key feature.

Negatives.

• No invasion of the capsule - see follicular thyroid carcinoma.
• No nuclear features suggestive of papillary thyroid carcinoma.

DDx:

• Thyroid gland nodular hyperplasia with an encapsulated nodule - not as cellular.
• Follicular thyroid carcinoma.
• Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP).
• Papillary thyroid carcinoma follicular variant.

Images

• 

  FA - extremely low mag. (WC)

• 

  FA - very low mag. (WC)

• 

  FA - low mag. (WC)

• 

  FA - intermed. mag. (WC)

• 

  FA - high mag. (WC)

• 

  FA - very high mag. (WC)

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Left Hemithyroid, Hemithyroidectomy:
- Follicular adenoma.
- Parathyroid gland.
- Five benign lymph nodes (0/5).
- NEGATIVE for evidence of malignancy.

Block letters

LEFT THYROID, SUPERIOR POLE, EXCISION:
- FOLLICULAR ADENOMA, MAXIMAL DIMENSION 5 MM.
- LYMPHOCYTIC THYROIDITIS.
- NODULAR HYPERPLASIA.
- NEGATIVE FOR MALIGNANCY.

Micro

The section shows a well-circumscribed lesion encapsulated by a thick fibrous capsule (~0.4 mm thick).

The lesions consists of microfollicles with a dense appearing colloid. The nuclei have round regular nuclear membranes. Small indistinct nucleoli are seen at high power.

Focally, the lesional cells overlap. However, the chromatin is not cleared. Nuclear grooves are not readily apparent and nuclear pseudoinclusions are not readily identified.

See also

• Thyroid gland.