Case Of The Month -January 2006

Follicular Neoplasms of Thyroid

INTRODUCTION: THE THYROID GLAND

ANATOMY/PHYSIOLOGY

• Bi lobed endocrine organ; 20 to 25 grams
• Either side of trachea and oesophagus
• Produces thyroxine under influence of TSH

NORMAL HISTOLOGY

• Consists of numerous follicles
• Follicles are lined by single layer of cuboidal (follicular) cells
• Thyroglobulin (colloid) within these follicles where there is a store of T3 and T4 hormones

NORMAL CYTOLOGY

• Follicular cells and colloid
• Colloid stains blue/mauve with Diff Quik
• Not uncommon to find pseudo-giant cells which are intact follicles

DEFINITIONS

• “Follicular lesions” include nodules of goitre, follicular adenomas and carcinomas and follicular variants of papillary ca.
• “Goitre” means any thyroid enlargement – benign or malignant, but generally is in reference to benign, non-neoplastic hyperplasia and colloid storage.
• “Follicular neoplasms” include both follicular adenomas and carcinomas

FOLLICULAR NEOPLASM (ADENOMA)

• Most common of thyroid neoplasms
• Clinically, there is a range of appearances – reflected on cyto preps
• Well circumscribed capsule (solitary mass)
• Difficult to distinguish histologically between ca and adenoma
• Because cytologic changes merge imperceptibly, it is often difficult to differentiate among goitres, adenomas and carcinomas

CLINICAL

• Present as a solitary nodule, usually as a painless mass.
• It may be found during a routine physical examination
• Nodule is smooth and discrete

CYTOLOGY

• Cellular smears
• Many equal sized cell clusters scattered throughout smear (microacinar/rosette like clusters from follicles)
• microfollicles
• Disorganized syncytial cell aggregates
• Scanty colloid which may appear as small inspissated globules
  (resembling psamomma bodies)
• Askanazy cell change
• Generally, epithelial cells appear bland, with minimal variation of appearance and a repetitive pattern of cell groups. However, atypical features may be present: nuclear crowding, karyomegaly, frequency/number of nucleoli raised, nuclear membrane irregularity + irregular chromatin distribution

Case 1

Cytology

The preparations are moderately cellular and show microfollicular groups with some nuclear variation and nuclear overlapping present. The features raise the possibility of a follicular neoplasm and further investigations are recommended.

Histology

MICRO
Sections confirm the presence of a nodule composed of follicular elements. In part the lesion shows a solid pattern of cells, in other parts there is a microfollicular pattern and in yet other areas there is a hyaline sclerosing pattern. Special stains for amyloid and for chromogranin are negative. The lesion extends to the ink cut margin in areas. Elsewhere there is a thin capsule but there is no unequivocal capsular or vascular invasion seen. There is minimal nuclear pleomorphism in the lesion and mitoses are not a feature. The surrounding thyroid tissue shows changes of focal lymphocytic thyroiditis.

SUMMARY:
LEFT THYROID LOBE - FOLLICULAR ADENOMA AND FOCAL LYMPHOCYTIC THYROIDITIS

Case 2

Cytology

A cellular sample comprised of groups of follicular epithelial cells, many showing a microfollicular pattern with oncocytic [Hurthle cell] change. The features are consistent with a follicular lesion, it is not possible to separate Hurthle cell adenoma from Hurthle cell carcinoma in this material.

Histology

MICRO
The sections show an encapsulated nodule of cellular thyroid tissue with a nodular growth pattern, with areas of compressed atrophic thyroid adjacent to the capsule, and normal thyroid on the isthmic aspect. The lesion is composed of nodules which have predominantly trabecular and focally a microfollicular growth pattern. There is no transcapsular or vascular invasion. There is no necrosis. Mitoses are sparse. There is only mild focal cytologic atypia.

The features are consistent with a follicular adenoma.

SUMMARY:
RIGHT LOBE THYROID - FOLLICULAR ADENOMA.

DIAGNOSTIC DIFFICULTIES

• Contamination by blood may make diagnosis difficult
• To distinguish from nodular goitre:
  • May be impossible to do so in some instances
  • Some solitary adenomas with large follicles and abundant colloid will yield the same findings as colloid goitre.
• To distinguish from well differentiated follicular carcinoma (generally):
  • Ca more cellular
  • Ca composed of crowded disorganised clusters, with large nuclei
  • Ca has more prominent nucleoli + more irregular chromatin
• Papillary carcinoma
  • If papillae are not removed intact by needle, the cells present as monolayered sheets – can hence be interpreted as follicular neoplasm
  • Also, these sheets may contain cells with dense cytoplasm, resembling squamous metaplasia or Askanazy cell change – these seen in follicular neoplasm
  • Intranuclear inclusions which can be seen in up to 90% of papillary ca, can occasionally be present in follicular neoplasms

Thanks to Dianne and Abed for submitting this case