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Lesiones foliculares citológicamente benignas

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Características citológicas diagnósticas       

  • Baja o moderada celularidad
  • Células cohesivas
  • Patrón de predominio microfolicular
  • Células foliculares uniformes, regularmente espaciadas.
  • Núcleos redondos, cromatina finamente granular
  • Citoplasma escaso o moderado
  • Algunos macrófagos
  • Núcleos desnudos

El coloide es usualmente abundante, aparece como gotas amorfas o como una película delgada translúcida con burbujas y fisuras lineares.

Algunas lesiones foliculares benignas son hipercelulares y  pueden presentar atipia citológica focal. Pueden encontrarse ocasionales células alargadas, en forma de huso, representando elementos del estroma reactivo o células foliculares alteradas recubriendo áreas de degeneración quística. También pueden ocurrir cambios de células de Hurtle focales. Si los microfolículos son escasos y la atipia es focal, se debe realizar un diagnóstico de un nódulo benigno citológicamente, aun si la muestra es celular. Los pacientes con este diagnóstico tienen que tener un seguimiento a intervalos apropiados.

A microbiopsy from a nodular goitre. A thick fragment in which round 3D follicles are separated by collagenous stroma. Orangiophilic colloid is visible inside some follicles whose contours are round. Where thinner a monolayer arrangement can be identified. 
Bland thyrocytes in a microfollicular arrangement. A monolayered sheet of bland thyrocytes with bland chromatin and moderate amount of pale, delicate cytoplasm. In the upper corner a follicle lined by similar cells is observed.  
Bare nuclei and microfollicles. Few microfollicles lined by uniform cells with delicate cytoplasm, round nuclei with fine chromatin and surrounded by bare nuclei (MGG).
A very low power view of a cellular lesion. A very lower power view of a MGG stained smear from a follicular lesion. It is very cellular, colloid is not visible and the cells are arranged in sheets, follicles or lie singly. At this magnification no commitment can be made as whether it is benign, suspicious or malignant. 
At high power the cells are uniform. A microfollicular pattern of regular, uniform thyroid cells exhibiting some “flaring” at their surface, usually seen in functioning cells; they are also monolayered and no reowding is observed.
A trabecular arrangement. The same cells may exhibit a trabecular arrangement; in this case the minimal degree of anisonucleosis is well within normal limits. Anisonucleosis (variability in the volume but not the shape of nuclei) is of very little significance in all endocrine glands and is certainly not a criteria for malignancy (MGG).
Bland, less cohesive thyrocytes. Nuclear detail is better seen in Papanicolaou stain: chromatin is fine and small chromocentres can be seen. Nuclear membrane is regular and thin while cytoplasm is delicate and transparent.
A cellular aspirate at low power. A medium power view of a microfollicular adenoma (MGG). At this magnification lack of background colloid, uniformity of cells and microfollicular pattern are obvious. In the absence of nuclear atypia, crowding or papillary architecture these lesions are classified differently either as follicular lesion, cytologically benign, Thy3 or follicular lesion – indeterminate. In all cases the physician must know that criteria to predict a well differentiated follicular carcinoma are only histological following excision of the lesion to search for capsular or vascular invasion. However an aggressive surgical approach will result in many benign lesions being excised.  
The cells are uniform and arranged in follicles. The same lesion at higher power confirms lack of nuclear atypia and a dominant microfollicular pattern. Bare nuclei are seen in the background, a feature which is reassuring as it is usually associated with benign lesions. 

A microfollicular pattern:

A microfollicular pattern. A microfollicular pattern (MGG); cells appear uniform and no crowding is observed, however few discohesive cells maintain their cytoplasm. 
A stromal fragment with mesenchymal nuclei. At MGG stroma is pinkish and fibrillary with mesenchymal cells appearing as elongated and usually hyperchromatic nuclei; the thyroid cells maintain a follicular architecture and are not arranged perpendicularly to the stroma as expected in a papillary lesion. 
A monolayered sheet of bland thyrocytes. A sheet of monoyared bland thyrocytes surrounded by smaller follicles and bare nuclei. 
A microfollicular arrangement. Bland follicles and bare nuclei. 

Adenoma follicular

Esta es una neoplasia benigna, que se presenta como un nódulo individual, usualmente no es mayor de 3cm de diámetro. Algunos de estos pueden producir hormonas tiroideas y consecuentemente causar hipertiroidismo (adenomas funcionales o “calientes”). El patrón histológico puede variar: macrofolicular (compuesto de grandes folículos llenos con coloide), microfolicular (con folículos mas pequeños), trabecular (con células foliculares organizadas en cintas)

Clasificación (Sin significado pronóstico)

  • Simple
  • Microfolicular
  • Trabecular
  • Oxifílico
  • Atípico
  • Papilar
  • Células en anillo de sello
Nodular hyperplasia Follicular neoplasia
multiple solitary
poorly encapsulated encapsulated
architectural heterogeneity uniformity of the architecture
cytologic heterogeneity cytologic homogeneity
comparable areas in adjacent gland different from surrounding gland
no compression of surrounding gland compression of surrounding gland

Microfollicular groups:

Microfollicular groups – These microfollicles are lined by thyrocytes showing a round nucleus with ‘open’ chromatin, abundant clear delicate cytoplasm with ‘flares’. These findings are in keeping with functioning cells. 
Microfollicular groups – This follicular aggregate shows uniform, bland thyrocytes with delicate, clear cytoplasm but no ‘flares’. There is no cytological atypia. A benign follicular lesion may be suggested if the colloid/cells ratio is low and bare nuclei are present in the background. 
Microfollicular adenoma (histology) – A low power view of a histologic section of an adenoma which is clearly separated from the surrounding thyroid tissue (Masson Trichrome stain).