Fig. 4.1
Thyroid cyst fluid (Diff-Quik stain, high power). Hemosiderin-laden macrophages in a background of watery colloid. Note that hemosiderin stains deep blue with Diff-Quik stain.
Fig. 4.2
Benign follicular/colloid nodule with “flame cells” (Diff-Quik stain, high power). In this example of a benign colloid nodule, “flame” cells with cytoplasmic vacuoles are seen. These cells are primarily seen in benign nodules with an overproduction of thyroid hormone.
Fig. 4.3
Benign follicular/colloid nodule (Papanicolaou stain, high power). Honeycomb arrangement of follicular cells with evenly spaced, round nuclei and no nuclear features of papillary thyroid carcinoma.
Triage
Benign nodules that are hypocellular or have a predominance of cyst contents may benefit from liquid based cytology to facilitate identification of follicular cells. In cases with a prominent lymphoid population, cytological or clinical features that are concerning for a lymphoproliferative disorder should prompt collection of additional material for flow cytometry. Some laboratories allocate material for molecular studies on all thyroid FNAs at the time of the procedure, in case the final diagnosis is indeterminate.
Differential Diagnosis
The main differential diagnostic consideration is a papillary thyroid carcinoma (PTC) with colloid or cystic changes. Nuclear features help to differentiate benign entities from PTC and are best appreciated on alcohol-fixed material. Lymphocytic thyroiditis also raises the possibility of ectopic cervical thymic tissue or a lymphoproliferative disorder.
Pearls
According to The Bethesda System for Reporting Thyroid Cytology (TBSRTC) [10], which is discussed in detail below, cases with abundant colloid, focal atypia, or features of lymphocytic thyroiditis do not require six groups of ten cells for adequacy. Thus, these cases should not be reported as non-diagnostic, but rather benign (for abundant colloid and features of lymphocytic thyroiditis) or atypia/follicular lesion of undetermined significance (for focal atypia).
In contrast, cases with abundant cyst contents should be meticulously examined and if there are insufficient follicular cells, they should be classified as non-diagnostic with a note that PTC with cystic changes cannot entirely be excluded.
Imaging studies are an important part of the evaluation of a thyroid lesion. When the cytological findings do not correlate with the radiological impression, failure to sample the targeted lesion should be considered.
4.2.2 Malignant Thyroid Nodules
Clinical Features
The main thyroid malignancies in the pediatric population include PTC, follicular carcinoma, Hürthle cell or follicular oncocytic carcinoma, medullary thyroid carcinoma, and lymphoma. Metastatic neoplasms are more common in adults, but can rarely be seen in children as well. PTC accounts for the vast majority (80–95 %) of pediatric thyroid malignancies, and is the third most common solid tumor in the pediatric population. Previous radiation is a risk factor for development of PTC and 7–11 % of patients have a history of previous radiation [11, 12]. Up to 40–80 % of pediatric patients have metastatic disease at presentation, [6, 12, 13] and FNA of radiologically suspicious lymph nodes is frequently performed prior to surgery, and occasionally concurrently with the thyroid FNA to guide decisions regarding dissection of the lymph node chains. Follicular carcinoma accounts for most of the remainder of malignancies (5–15 %). Medullary thyroid carcinoma is uncommon (3–5 %), and frequently associated with familial cancer syndromes [3, 6, 8]. Multiple Endocrine Neoplasia (MEN) Types 2A and 2B are characterized by point mutations in the RET proto-oncogene and patients develop medullary thyroid carcinoma and pheochromocytoma. MEN 2A patients also have hyperparathyroidism, while MEN 2B patients have mucosal ganglioneuromas and Marfanoid habitus. Patients with MEN2 inevitably develop medullary thyroid carcinoma and thus, prophylactic thyroidectomy is recommended in early childhood.
Cytological Features
Follicular carcinomas show predominantly microfollicular architecture with scant colloid and high cellularity. Nuclear features of PTC are not seen in these tumors. Since vascular and capsular invasion cannot be assessed on FNA specimens, these cases are typically classified as suspicious for follicular neoplasm by TBSRTC [10] (Fig. 4.4).
Fig. 4.4
Suspicious for follicular neoplasm (a. Diff-Quik stain, high power; b. Papanicolaou stain, high power). Cellular clusters with prominent microfollicles and overlapping nuclei, seen in a background of scant colloid. This was follicular carcinoma on excision.
Classic PTC is more common in the pediatric population and may show true papillary tissue fragments with dyscohesive tumor cells surrounding a fibrovascular core, in addition to cells in sheets and follicular arrangements. The nuclear features include pale, evenly dispersed, fine chromatin, nuclear grooves, intranuclear pseudoinclusions, and small peripherally placed nucleoli (Fig. 4.5). In contrast to classic PTC, the follicular variant of PTC (FVPTC) and non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) lack true papillary fragments, and often has a greater number of microfollicles. Nuclear features of PTC may be subtle or absent in FVPTC and NIFTP. The background may have thick colloid, multinucleated giant cells, and/or atypical histiocytoid cells with cytoplasmic vacuolization.
Fig. 4.5
Papillary thyroid carcinoma (a. Diff-Quik stain, low power; b. Papanicolaou stain, high power). Papillary tissue fragments composed of crowded follicular cells with oval nuclei. The Papanicolaou stain (b) highlights prominent nuclear grooves, powdery chromatin and small nucleoli.
Medullary thyroid carcinoma typically yields cellular aspirates with loosely cohesive and isolated tumor cells. The tumor cells are most often plasmacytoid, but spindled and/or round forms may also be seen. The cells have abundant granular cytoplasm and round to spindle nuclei with stippled chromatin (Fig. 4.6). Amyloid, which is indistinguishable from thick colloid on Papanicolaou-stained smears and may be metachromatic on modified Giemsa-stained preparations, may also be present in the background. Medullary thyroid carcinoma is positive for synaptophysin, calcitonin, TTF1, and carcinoembryonic antigen (CEA), while negative for thyroglobulin.
Fig. 4.6
Medullary thyroid carcinoma (a. Diff-Quik stain, low power; b. H&E stain, low power). The tumor cells in this case of medullary carcinoma are relatively monomorphic, epithelioid and plasmacytoid. On the cell block (b), they appear oncocytic. Strong positive staining for calcitonin and neuroendocrine markers, in addition to positivity for a RET gene mutation, solidified the diagnosis of medullary thyroid carcinoma arising in the setting of multiple endocrine neoplasia (MEN). (Image courtesy of Dr. Sara Monaco).
Triage
Some thyroid malignancies may benefit from molecular studies. In addition, molecular studies may be helpful prior to resection, especially if there is an indeterminate cytological diagnosis. If medullary carcinoma is suspected, a cell block should be prepared to facilitate confirmatory special and immunohistochemical stains.
Differential Diagnosis
The possibility of a hyperplastic colloid nodule should be considered in cases with abundant colloid and little cytological atypia. In PTC with cystic changes, the epithelial cells may have small cytoplasmic vacuoles and atypical nuclear features, thereby mimicking histiocytes (e.g., atypical histiocytoid cells), but are positive for TTF-1 and cytokeratin, and negative for CD68 [13]. Similarly, PTCs, especially those metastatic to lymph nodes, can mimic clusters of histiocytes, reactive germinal centers, and granulomatous inflammation. However, in this setting, the presence of nuclear features of PTC helps to exclude these entities. In addition, immunohistochemical stains help to confirm the diagnosis of a thyroid malignancy, and distinguish it from other benign and malignant processes.
Pearl
In aspirates from lymph nodes lateral to the jugular vein, benign-appearing thyroid elements (colloid and follicular cells) should prompt serious consideration of a metastatic PTC, even if nuclear features of PTC are not clearly identified. However, in aspirates obtained from what radiologically appears to be a lymph node more medially in the neck, benign-appearing thyroid elements may represent rests of thyroid tissue along the embryological path of descent and warrant cautious interpretation. Similarly, in patients with dyshormonogenetic goiter, a portion of the multilobulated thyroid gland may be radiologically interpreted as a separate discrete mass or “lymph node,” leading to misdiagnosis of metastatic carcinoma.
4.2.3 Reporting of Thyroid FNAs
The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) was developed in 2007–2010 as a standardized system of reporting thyroid fine needle aspiration biopsies with an implied risk of malignancy and recommended clinical management [10]. The system consists of six diagnostic categories with further descriptive diagnoses: Non-diagnostic, Benign, Atypia of Undetermined Significance or Follicular Lesion of Undetermined Significance, Follicular or Oncocytic Neoplasm or Suspicious for a Follicular or Oncocytic Neoplasm, Suspicious for Malignant Cells, and Malignant.
Although TBSRTC was largely developed based on adult data, there are two studies evaluating the application of TBSRTC to the pediatric population, which have shown an incremental increase in the risk of malignancy among the categories [7, 14]. However, in each category, the risk of malignancy is higher in the pediatric population. This is due to an overall higher incidence of malignancy (10–14 % in adults vs 20–35 % in children [3, 7]) and a lower incidence of benign neoplastic nodules (Table 4.1).
Table 4.1
Correlation of diagnostic categories by TBSRTC with the risk of malignancy overall and in studies restricted to pediatric populations
Diagnostic category | Risk of malignancy (%)a | Risk of malignancy in children (%)b |
|---|---|---|
Benign | 0–3 | 2–7 |
Atypia of undetermined significance (AUS/FLUS) | 5–15 | 28–40 |
Suspicious for follicular or oncocytic neoplasm | 15–30 | 58–100 |
Suspicious for malignant cells | 60–75 | 40–100 |
Positive for malignant cells | 97–99 | 100 |
4.2.3.1 Summary of TBSRTC Diagnostic Categories
In order to be adequate, an FNA must have a minimum of six groups of cells with at least ten follicular cells per group. Exceptions include cases with cytologic atypia in evaluable cells, nodules in a background of lymphocytic thyroiditis, and colloid nodules showing abundant colloid. A summary of TBSRTC categories is seen in Table 4.2.
Table 4.2
Diagnostic categories for the Bethesda System for Reporting Thyroid Cytopathology
Category | Cytological features | Recommended management |
|---|---|---|
Unsatisfactory/Non-diagnostic | Inadequate samples include cases with fewer than six groups of ten cells each (acellular or hypocellular), cases with technical problems limiting interpretation (staining, preservation, obscuring artifacts), and cases with cyst fluid only. | Repeat FNA after 3 months. However, if the cyst is drained upon aspiration and there is no remaining nodule, then a non-diagnostic FNA may be presumably negative for malignant cells, but radiological correlation is essential. |
Benign | Aspirates typically show abundant colloid and moderate cellularity with follicular cells arranged in a two-dimensional sheets (benign colloid nodule, hyperplastic colloid nodule), or features of lymphocytic thyroiditis. Pediatric follicular cells may show a tighter arrangement than adult benign tissue, but an orderly arrangement without overlapping of nuclei should be visible. | Clinical follow-up, as needed. However, most studies report a 1–3 % false negative rate for benign thyroid FNAs, thus radiological correlation is essential with a negative diagnosis. |
Atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) | Cases with cytologic atypia or architectural atypia that is insufficient for a definitive diagnosis of suspicious for follicular neoplasm or malignancy. This includes cases with prominent microfollicles in a case that is otherwise benign or scantly cellular, cases that show predominantly oncocytic cells in a benign background, cases with cellular crowding due to clotting artifact or other obscuring factors, and cases with focal cytological atypia suggestive of papillary thyroid carcinoma. | Repeat FNA in 3–6 months. However, in the pediatric population, up to 40 % of these cases are malignant on excision [7, 14]. Thus, in conjunction with the clinical and radiological picture, some clinicians may choose to take the patient directly to surgery, especially if the patient has two AUS/FLUS diagnoses where the risk of malignancy approaches that of the suspicious for follicular neoplasm category. |
Suspicious for follicular or oncocytic neoplasm | More cellular smears with significant crowding and overlapping of nuclei. There may be significant microfollicle formation. The nuclei are monotonous and slightly hyperchromatic. The key to diagnosis is the cellularity of the samples, lack of colloid, and the architecture of the clusters. In adults, the majority of cases with this diagnosis turn out to be follicular adenomas or follicular variant of papillary thyroid carcinoma, with a smaller proportion of follicular carcinomas. In the pediatric population, 60–100 % of these cases are malignant, usually papillary thyroid carcinoma [7, 14]. | Partial thyroidectomy is recommended for this category given the risk of malignancy. However, due to the high rate of malignancy in the pediatric population, clinicians may request molecular testing and based on the results, may choose to go directly to total thyroidectomy. |
Suspicious for malignant cells | Most of the cases in this category are suspicious for papillary thyroid carcinoma; however, cases can also be suspicious for lymphoma, medullary thyroid carcinoma, metastatic carcinoma, or other malignancies. These cases usually quantitatively or qualitatively fall short of being diagnostic of malignancy. | Recommended management for cases suspicious for papillary thyroid carcinoma is usually a total thyroidectomy. Cases suspicious for lymphoma or metastatic neoplasms typically undergo repeat biopsy. |
Positive for malignant cells (papillary carcinoma, medullary carcinoma, metastatic malignancy, lymphoma) | Cases of papillary thyroid carcinoma show abundantly cellular smears with characteristic nuclear features, including intranuclear inclusions, nuclear grooves, chromatin clearing. Cases of medullary carcinoma, metastatic malignancies, or lymphoma, are likewise highly cellular with morphologic and immunophenotypic features characteristic of the particular entity. | Recommended management for papillary thyroid carcinoma is total thyroidectomy. In the pediatric population, lymph node sampling should be considered due to the high rate of metastasis at the time of diagnosis. |
4.2.4 Molecular Testing in Thyroid FNA
In the adult population, molecular testing is performed on cytological specimens from the thyroid in order to refine the cytologic diagnosis and thereby aid in management. In the case of an indeterminate cytologic diagnosis (e.g., AUS/FLUS, suspicious for follicular neoplasm, or suspicious for malignancy), the presence of mutations common in malignancy, particularly the BRAF mutation, may lead to more aggressive follow-up or surgical therapy. However, the distribution of genetic mutations is different in the children and adolescents than in the adults, and the utility of genetic testing in the pediatric population is unclear [11, 15–17].
4.2.4.1 BRAF Mutations
Mutations in the BRAF gene, virtually all the 1799 T > A point mutation resulting in the V600E single amino acid substitution, are seen in up to 70 % of adult PTC and are associated with a more aggressive clinical course. Accordingly, testing for this mutation is increasingly offered in adult thyroid aspirates. However, this mutation is reported to be much less frequent in the pediatric population, being seen in 0–20 % (overall 7 %) of pediatric cases [16].
4.2.4.2 RET/PTC Rearrangements
Translocations of the RET proto-oncogene on chromosome 10 are seen in 40–70 % of sporadic pediatric PTC, compared to less than 40 % in adults [11, 15]. There are three common translocations referred to as RET/PTC1, RET/PTC2, and RET/PTC3. Some studies have indicated a higher incidence of RET/PTC1 in sporadic PTC and a higher incidence of RET/PTC3 in radiation induced carcinoma [15]. Currently genetic testing for these translocations is performed in the clinical setting in some laboratories.
4.2.4.3 PAX8/PPAR Gamma Rearrangements and RAS Mutations
A translocation between the PAX8 gene and the PPAR gamma gene is seen in 20–50 % of adult follicular carcinoma of the thyroid [16]. Follicular carcinomas that do not have this translocation are frequently associated with RAS mutations. However, these changes are also seen in follicular adenomas and are not specific for carcinoma. Genetic testing for these changes is not commonly performed on aspirates in the clinical setting.
4.3 Salivary Gland
Lesions in the salivary glands include neoplasms, congenital vascular or cystic masses, and inflammatory lesions. True salivary gland epithelial neoplasms are rare in the pediatric population, but are largely benign. Intraparotid lymph nodes may present as a palpable mass or incidental radiologic finding. In addition, tumors of the connective tissues including benign lesions such as nodular fasciitis and solitary fibrous tumor or malignant lesions such as malignant peripheral nerve sheath tumor and rhabdomyosarcoma can involve the salivary glands (Personal archives, 19). Pilomatrixoma or other lesions of the skin or soft tissue overlying the parotid have also been mistaken for parotid masses.
4.3.1 Benign Salivary Gland Lesions
Clinical Features
Most of the benign salivary gland lesions can be grouped into lymphoid or inflammatory lesions and cystic lesions. Benign lymphoid lesions include chronic sialadenitis, lymphoepithelial cysts, and intraparenchymal lymph nodes. Inflammatory lesions include acute sialadenitis or sialolithiasis, and chronic fibrosing sialadenitis (Kuttner tumor).
Cytological Features
Benign intrasalivary lymph nodes and chronic inflammatory processes are characterized by variable amounts of benign salivary tissue in a background of a heterogeneous lymphoid population with a predominance of small lymphocytes and intermixed histiocytes. Squamous or mucinous metaplasia may be present. Chronic sialadenitis can be associated with dense fibrosis, which clinically presents as a hard tumor-like mass, and may yield scantly cellular aspirates with stromal fragments. Acute sialadenitis has abundant neutrophils and inflammatory debris, and special stains for organisms should be performed in these cases. Cystic lesions include sialoceles and lymphoepithelial cysts, as well as extrasalivary cystic lesions such as thyroglossal duct cyst or branchial cleft cyst. Meticulous examination for the presence and type of cyst lining cells and correlation with radiology is essential.
Triage
A cell block can be prepared from the needle rinses or additional dedicated passes, and can be used for special stains, such as for microorganisms, or immunohistochemical stains. If a lymphoid lesion is concerning for lymphoma, additional material should be collected for flow cytometry. Acute inflammatory lesions should prompt collection of additional material for microbial cultures.
Differential Diagnosis
The main differential diagnostic considerations for lymphocytic lesions include reactive lymphoid processes in extrasalivary lymph nodes or adjacent soft tissues and lymphomas. In addition, lymphocyte-rich aspirates with a dirty background should raise the possibility of Warthin tumor, although this entity is exceedingly rare in the pediatric population. Acute sialadenitis can mimic an abscess or acute suppurative lymphadenitis.
Pearls
Many benign or inflammatory salivary gland lesions can be associated with metaplastic changes, such as squamous or mucinous metaplasia, which may raise concern for neoplasms such as low grade mucoepidermoid carcinoma. A conservative approach is recommended if mucinous and/or squamous features are focal, to avoid an erroneous diagnosis of malignancy.
4.3.2 Salivary Gland Neoplasms
4.3.2.1 Introduction and Classification
Clinical Features
Salivary gland neoplasms are rare in the pediatric population, accounting for 3–8 % of all salivary gland neoplasms and 0.5 % of all pediatric malignancies [19, 20]. Most pediatric salivary gland lesions are benign (60–75 %) with pleomorphic adenoma comprising the vast majority of benign neoplasms (>90 %) [18, 19, 21, 22]. Scattered cases of myoepithelioma, Warthin tumor, and sebaceous lymphadenoma have been reported [19, 21]. Malignant lesions of the salivary gland are much less common, comprising 25–40 % of cases. The majority of these cases (50–80 %) are mucoepidermoid carcinoma, followed by a smaller proportion of acinic cell carcinoma (13–25 %) [18, 19, 21, 22]. Most lesions occur in adolescents; less than 10 % of patients are less than 10 years old at diagnosis [19, 21]. There is a slight female predominance. Tumors in very young patients (<5 years old) may include metastatic or mesenchymal malignancies, of which neuroblastoma, rhabdomyosarcoma , undifferentiated sarcoma, and epithelioid sarcoma have been reported [24, 25]. The parotid gland is most often affected (45–80 %), followed by the submandibular gland (10–25 %) [19, 22].
Cytological Features
Salivary gland neoplasms are best characterized by the type of cells present, the degree of atypia, and the presence or absence of stromal material. Cases with cells and stroma, so-called biphasic lesions, should describe the qualities of the cells (e.g., basaloid with scant cytoplasm, oncocytic with moderate-to-abundant granular cytoplasm, or pleomorphic with marked nuclear pleomorphism) and the qualities of the mesenchymal material (e.g., fibrillary, dense/hyaline, or rounded globules). If mucin is present, this should also be noted. A summary of the differential diagnosis for the various cytomorphological patterns described in the literature is seen in Table 4.3 [23].
Table 4.3
Correlation of cytomorphological pattern with morphological features and differential diagnosis in salivary gland lesions
Cytomorphological pattern | Cytomorphology | Differential diagnosis |
|---|---|---|
Basaloid neoplasm without stroma | Cellular smears with monomorphic cells containing scant cytoplasm. The cells should show at least some cohesion, but also can be seen as single, plasmacytoid or spindled cells. | • Cellular monomorphic adenoma • Basal cell adenoma/carcinoma • Basaloid squamous cell carcinoma • Lymphoma • Neuroendocrine tumors • Pilomatrixoma • Metastatic round blue cell neoplasm |
Basaloid neoplasm with stroma (Biphasic neoplasm) | Cellular smears with monomorphic cells with scant cytoplasm, within a background of metachromatic stromal material such as fibrillary fragments or dense hyaline globules. | • Pleomorphic adenoma • Adenoid cystic carcinoma • Polymorphous low grade adenocarcinoma • Mammary analog secretory carcinoma • Mesenchymal neoplasms (e.g., solitary myofibroma) |
Oncocytic neoplasm | Cellular smears with monomorphic cells with moderate-to-abundant granular cytoplasm. Background may show lymphoid cells in the setting of Warthin tumor. | • Oncocytoma • Warthin tumor • Acinic cell carcinoma • Salivary duct carcinoma |
Pleomorphic neoplasm | Cellular smears with malignant cells with marked nuclear pleomorphism. | • Salivary duct carcinoma • Squamous cell carcinoma • High grade lymphoma • Sarcoma (e.g., MPNST) • Metastatic malignancy |
Lymphocyte-rich lesion or neoplasm | Cellular smears with discohesive cells with scant cytoplasm within a background of lymphoglandular bodies. | • Lymphoepithelial cyst • Warthin tumor • Intraparotid lymph node • Lymphoma • Metastatic round blue cell tumor • Acinic cell carcinoma • Mucoepidermoid carcinoma |
