|Year : 2014 | Volume
| Issue : 1 | Page : 16-22
Histopathological features of Papillary Thyroid Carcinoma with special emphasis on the significance of nuclear features in their diagnosis
Deepa Thomas Kunjumon, Krishnaraj Upadhyaya
Department of Pathology, Yenepoya Medical College, Yenepoya University, Mangalore, Karnataka, India
|Date of Web Publication||4-Jun-2014|
Deepa Thomas Kunjumon
Department of Pathology, Yenepoya Medical College, Yenepoya University, Derlakatte, Mangalore - 575 018, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Papillary carcinoma (PTC) is the most common thyroid malignancy comprising 80-85%. In addition to papillary architecture, nuclear features like clear, ground glass or Orphan Annie-eyed appearance, oval shape, increased nuclear size, hypodense chromatin, intranuclear cytoplasmic inclusions, nuclear grooving, nuclear overlapping, and mitotic figures play a vital role in the diagnosis although some of the features may be seen in other diseases of thyroid. Objectives: To evaluate and establish the diagnostic significance of each nuclear feature in PTC. Settings and Design: Among the thyroidectomy specimens received in the department of pathology, only the PTC cases were chosen. Multiple sections were studied from the tumor by two different pathologists with a special emphasis on morphological and nuclear features. Statistical analysis: Fischer's exact test was done to find the correlation between the grading of nuclear features and cell population. Materials and Methods: Forty-one PTC cases were studied. Many H and E-stained slides of the tumor were studied by two different pathologists, and average of both observers was analyzed with special reference to nuclear features in classical and other variants of PTC. Results: The study evaluated that the ground glass nuclei, nuclear grooving, and nuclear overcrowding were the most common features seen in all (100%) cases though percentage of cells exhibiting these features varied from tumor to tumor. Other features mentioned above were less frequently encountered (42%-95%). Conclusion: In PTC, especially in variants, nuclear features are of utmost importance as they have to be differentiated from other thyroid diseases presenting with similar architectural morphology. Hence, more tissue sections have to be screened.
Keywords: Nuclear features, papillary carcinoma, variants
|How to cite this article:|
Kunjumon DT, Upadhyaya K. Histopathological features of Papillary Thyroid Carcinoma with special emphasis on the significance of nuclear features in their diagnosis. Arch Med Health Sci 2014;2:16-22
|How to cite this URL:|
Kunjumon DT, Upadhyaya K. Histopathological features of Papillary Thyroid Carcinoma with special emphasis on the significance of nuclear features in their diagnosis. Arch Med Health Sci [serial online] 2014 [cited 2020 Apr 10];2:16-22. Available from: http://www.amhsjournal.org/text.asp?2014/2/1/16/133786
| Introduction|| |
Thyroid cancer is the commonest of all endocrine malignancies. The overall annual incidence ranges from 0.5-10 cases/100,000 population. Most authors have reported an incidence of around 1% of all malignancies to be of thyroid origin. Most of the thyroid malignancies present as solitary thyroid nodules clinically indistinguishable from benign neoplasms and non-neoplastic nodules and pose great diagnostic challenge. FNAC and histopathology play a major role in solving this diagnostic challenge and help the clinicians in the management of these patients.
PTC comprises about 80-85% of thyroid malignancies. These common tumors tend to be biologically indolent and have an excellent prognosis. They can occur at any age and rarely has been diagnosed as a congenital tumor. Most tumors are diagnosed in patients in the third to fifth decades of life. Women are affected, and female to male ratio ranges from 2:1 to 4:1. Microscopically, PTC shares certain features. The neoplastic papillae contain a central core of fibrovascular tissue, which are lined by one or occasionally several layers of cells with crowded oval nuclei.
Initially, the diagnostic criterion used for the diagnosis of PTC was the presence of papillary growth pattern, but in the latter half of the last century, nuclear criteria gained much importance. In the past few decades, the nuclear features have become the diagnostic hallmark of the tumor.
The nuclei of PTC have been described as clear, ground glass, or Orphan Annie-eyed.  These nuclei are usually oval and larger than normal follicular nuclei containing hypodense chromatin. The other important nuclear features are nuclear grooving and intranuclear cytoplasmic inclusions, but both of which can be seen in both neoplastic and non-neoplastic diseases of thyroid. Nuclear overlapping is also a very common feature.
This present study was conducted with the following objectives:
- To diagnose and assess the frequency of classical and other variants of PTC by histopathological study;
- To assess and analyze various nuclear features encountered in these cases;
- To establish the diagnostic significance of the nuclear features.
| Materials and Methods|| |
The study consisted of analysis of histopathology of thyroid malignancies reported from May 2011 to April 2013 with clinical data. Multiple representative sections were taken from these specimens, which were stained by standard Hand E method. There were 41 papillary carcinoma. All were classified to different types- Classical, follicular, solid, microcarcinoma, tall cell, encapsulated, and columnar variants. Five to ten sections of the tumor were studied in detail by two different pathologists and average of both observers was analyzed with special reference to the following nuclear features such as
i. Ground glass appearance,
ii. Nuclear grooving,
iii. Nuclear crowding
iv. Dusty chromatin,
v. Pale chromatin,
vi. Intranuclear inclusion bodies,
vii. Mitotic figures.
Also, additional features like psammoma bodies and papillary architecture were studied. Grading of these features was performed based on percentage of cells exhibiting these specific features. The grading scale was 0- nil, 1+ was for less than 11% of cells, 2+ for 11-30% of cells, 3+ for 31-50%, 4+ for more than 50%. Around 50 high power fields were studied in each slide for each nuclear feature. The counting was done methodically starting from left hand side of section and moving strictly right, up, right, and down directions finishing in the extreme right of the section. A special care is taken to see that with every horizontal movement to the right, a minimum of 1 high power field gap is maintained so that no cells in the previous field are focused in the next field. The data obtained was scrutinized and analyzed. The Fischer's exact test was done to correlate between nuclear feature and cell population.
| Results|| |
Among the 41 cases of PTC, there were 23 classical variants, 12 follicular variants, 2 microcarcinomas, 1 case each of solid, tall cell, encapsulated, and columnar variants. Eleven (27%) were males and 30 (73%) were females. There were 16 females with classical variant (39%).
The tumor had a wide age range with maximum number of cases in the 20-40 years group (54%). In all the groups, the majority of the nuclei was round to oval with mild to moderate pleomorphism and showed varying degree of anisonucleosis. Among the 12 cases of follicular variant, 9 (75%) showed prominent (3+) ground glass nuclei as shown in [Figure 5] along with each of solid, tall cell, and columnar variants, thereby establishing its significance in diagnosis of variants. This is shown in [Table 1].
|Table 1: Grading of ground glass appearance in each papillary carcinoma variant |
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Regarding the nuclear grooving, 44% of cases had 2+ nuclear grooving that included 11 cases of classical type, 3 cases of follicular variant, and 1 case each of solid, microcarcinoma, tall cell variant, columnar variant, and encapsulated variant. This is shown in [Table 2].
Fifty-eight percent of cases showed prominent nuclear crowding (3+), which comprised of 17 classical, 2 follicular, 2 microcarcinoma, 1 each of tall cell, columnar, and encapsulated variants. This is shown in [Table 3].
A significant number of cases showed only 1+ dusty chromatin; this feature was again noted in all the variants. It was absent in only one classical type and one case of follicular variant. This is depicted in [Figure 6].
Pale chromatin was observed in only 49% cases inclusive of 15 classical types and 5 follicular variants as shown in [Figure 7]. Mitotic figures were also seen in 36% of cases only and that again included all the variants, except the encapsulated variant. But, it was not significant.
Intranuclear cytoplasmic inclusions were perceived in 63% of cases as 1+ grading, mainly in classical and follicular variants, but it were absent in the solid, microcarcinoma, tall cell, columnar, and encapsulated variants.
Out of the 12 cases of follicular variants, 11 had no papillary architecture as was the case with the single case of solid variant. The columnar variant showed 3+ grading and 1 microcarcinoma along with the tall cell variant showed 2+ grading of papillary architecture as shown in [Table 4].
A majority of cases (87%) did not show any psammoma bodies, thereby indicating that this feature was not frequently encountered. All the diagnostic features with their grades are shown in [Table 5].
| Discussion|| |
The study by Elsheikh et al. revealed that some experts have exhibited a relatively lower threshold for the identification and/or diagnostic significance of PTC like nuclei than others.  Only a limited number of studies have been done in the past to evaluate the diagnostic significance of various nuclear features encountered in PTC. In addition, methodical quantification of the individual nuclear features was not commonly seen in the literature. Hence, in the present study, special emphasis has been placed to scrutinize the nuclear features in PTC and analyze the data in a systematic manner.
Many thyroid lesions can present with a papillaroid architecture mimicking PTC and pose diagnostic problem. These lesions include chronic lymphocytic thyroiditis, benign papillary hyperplastic lesions, hyalinizing trabecular neoplasms, and also the post-FNA tissue changes.  Hence, we have to be careful in identifying the true complex branching papillary architecture of PTC. Further, papillary architecture is never seen in variants of PTC, especially in the follicular variant. Therefore, diagnosis was purely based on the nuclear features.
Psammoma bodies are formed by focal areas of infarction of the tips of papillae, thereby depositing calcium on dying cells after which it leads to lamellation. Similar features are encountered in Hurthle cell hyperplasia and Hurthle cell neoplasms. But here, lamellation is absent. In our study, they were seen only in 5 out of 41 cases (12%) in contrast to 29% in a study by Hunt et al.  and 40% in other series.  This can probably be attributed to smaller number of cases in our study and relatively less number of fields screened in our study when compared to other series.
In reality, nuclear changes can be divided into 2 major categories:
- The clearing is said to be due to the disappearance, fine dispersion, or displacement of chromatin, thus giving a vesicular appearance of the nucleus;
- A number of morphologic alterations of the nuclear membrane, which then folds into itself to lead to semi-lunar nuclear forms having a finely serrated contour, longitudinal grooves, and pseudo inclusions. 
Ground glass appearance is not pathognomonic, because benign lesions such as nodular hyperplasia, follicular adenoma, Graves disease, and Hashimoto thyroiditis can also exhibit clear nuclei focally.  It was seen in 80% of the thyroid lesions  in other studies. In our study, ground glass appearance is the most common finding. One-hundred percent of cases presented this feature with 61% of them exhibiting 3+ grade. Although previous studies on nuclear features of PTC have revealed that ground glass nucleus and nuclear grooving can be seen in other neoplastic and non-neoplastic lesions of thyroid like Hashimoto's thyroiditis, adenomatous hyperplasia, diffuse hyperplasia, and in hyalinizing trabecular tumor, these features are significantly less common and less prominent in these lesions. The incidence of ground glass nuclei and nuclear grooving was 100% in our study in contrast to 33% in benign lesions of thyroid.  The ground glass appearance of nucleus is shown in [Figure 1].
Grooved nuclei can be well appreciated in cytologic preparations, and constitute a helpful diagnostic criterion of PTC in FNAC. However, nuclear grooving cannot be considered pathognomonic because it may be seen in other thyroid lesions including Hashimoto's disease, adenomatous hyperplasia, diffuse hyperplasia, and in hyalinizing trabecular tumor.  The ground glass empty-looking nucleus having peripherally marginated dusty chromatin is believed to be an artefact of formalin fixation because it is not seen in frozen section or cytological preparations. , Dusty chromatin is shown in [Figure 3]. Sometimes, if nuclei are not ground glass, the chromatin looks more evenly distributed or pale.This is shown in [Figure 4]. Sixty-eight percent had 1+ dusty chromatin and 49% had 1+ pale chromatin in our study. Occasionally, the nuclei may even exhibit coarse chromatin pattern with considerable pleomorphism. In such cases, the diagnosis of PTC would have to rest more on the architectural features, and on the identification of foci showing more diagnostic features. Nuclear grooving is shown in [Figure 2].
|Figure 2: Nuclear grooving (black arrow) and nuclear crowding (red arrow) - 40 X|
Click here to view
Nuclear pseudo-inclusions, which represent intranuclear herniation of pockets of cytoplasm, appear as pale-staining membrane-delineated vacuoles. They are typical of PTC, but are usually found in only a minority of the tumor cells and are not entirely pathognomonic.  In our present study, intranuclear inclusions were encountered only in 6% of classical and follicular variants similar to other studies. 
The enlarged irregular nuclei that are oval-shaped show nuclear crowding because of nuclear enlargement.  Both increased nuclear size and nuclear crowding were significant findings in our study, seen in all the 41 cases. Majority of the other studies have not given significant importance to these features. Nuclear crowding is shown in [Figure 2].
Mitotic figures are generally absent or sparse. However, in some highly invasive tumors, mitotic figures can be found more easily.  In our study, it was seen in all the variants but had a lower grade. Ninety-eight percent of cases were mitotically not active, exhibiting only 0-1 mitoses per 10 hpf; only in 2% cases, mitoses was more than 1 per 10 hpf implying that majority of the cases in our study are of low mitotic potential. This indicates that mitotic rate is not of great significance in PTC.
The neoplastic cells are said to be polygonal to cuboidal, dome-shaped, hobnailed, or columnar. The cytoplasm is lightly eosinophilic to amphophilic, but can exhibit oxyphilic or clear cytoplasm also. 
Since the differentiation of follicular variant of PTC from other follicular lesions like follicular carcinoma and follicular adenoma is extremely important, the diagnosis is exclusively based on nuclear features. ,
LiVolsi and Baloch preferred a scheme in which a diagnosis of follicular variant was made on an encapsulated lesion that shows any area having characteristic cytological features of PTC. ,
Chan suggested using stricter criteria for the diagnosis of follicular variant, which included evaluation of major and minor features. The four major features were as follows:
- Relatively oval nuclei than round,
- Crowding of nuclei with lack of polarity,
- Clear nuclear chromatin pattern or prominent nuclear grooves, and
- Presence of psammoma bodies. 
When only a one of these features is identified, the presence of all of the following listed subsidiary criteria should be present for the diagnosis. These minor criteria include:
- Occurrence of abortive papillae,
- Predominantly elongated and unevenly shaped follicles,
- Dark-staining colloid,
- Nuclear pseudo inclusions, and
- Multinucleated histiocytes in the lumen of the follicles. 
In our present study, majority of follicular variants showed most of the PTC-like nuclear features when compared to other studies.
When the solid growth represents 50% of the tumor mass, a diagnosis of solid variant of papillary carcinoma may be made. The nuclear features should be those of PTC.  The tall cell variant  is usually papilliferous and invasive. The nuclei, which are typical of those of PTC, are mostly basally located. In most of the studies, it constitutes 10.4% of PTC, but in our study, it was only 2.4%, which is comparable to 4% in Johnson's study.  In a study by Evan et al. of the columnar variant,  cells showed stratified, hyperchromatic nuclei, with inconspicuous nuclear grooves and single prominent nucleoli. Psammoma bodies were absent.  In our study, nuclear grooving was observed sparsely. The encapsulated variant constituted 2.4% of the cases in contrast to the 14% encountered in other studies. 
Similarly, 'papillary microcarcinoma,  was 4.8% as against a study in which it was 1.2%. 
In spite of these morphological features, the nuclear features are given greater significance for the diagnosis of PTC.
Fischer's exact test was done in our study, and it was found that for the PTC-like nuclear features like ground glass appearance, nuclear grooving, nuclear crowding, intranuclear inclusions, and papillary architecture, there was significant correlation for the grading. (P values = 0.003, 0.001, 0.0001, 0.0001, and 0.0001, respectively)
| Conclusion|| |
- In any of suspected cases of PTC, a detailed study of tissues should be performed to evaluate PTC-like nuclear features like ground glass appearance, nuclear crowding, and nuclear grooving for confirmation of diagnosis.
- In the diagnosis of PTC, especially the follicular variant, nuclear features are the only basis for the diagnosis.
- Although ground glass appearance, nuclear crowding, and nuclear grooving are not pathognomonic of PTC, presence of more than one feature is highly indicative of PTC, hence the need for detailed study.
Any thyroid neoplasm should be well evaluated by detailed study of nuclear features in order to rule out the possibility of PTC as it has excellent prognosis when compared to other malignancies of thyroid.
| Acknowledgement|| |
We thank Dr. K. Pushpalatha Pai, Senior Professor and Head of Department, Department, Yenepoya Medical College for her constant support and encouragement.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]