Doing More with Less: Fine Needle Aspiration Cytology in Pediatric Neoplasms.

BACKGROUND: Cancer is one of the leading causes of death in the pediatric age group following infections. Among the diagnostic modalities, fine needle aspiration cytology (FNAC) is increasingly recognized as it permits rapid diagnosis with low cost and complication. In this study, we emphasize the diagnostic value of FNAC and describe the cytomorphological spectrum of tumors diagnosed on FNAC in pediatric patients with or without the aid of ancillary tests.
MATERIALS AND METHODS: This retrospective study included a total of 614 patients under the age of 15 years for whom fine needle aspiration (FNA) was done during a period of 3 years with or without guidance. The cytology smears were reviewed, and the morphological spectrum was analyzed with the ancillary studies.
RESULTS: Aspirates from children constituted around 3.5% of the total FNAC performed in our Institute. Of the 614 cases, 336 were male, and 278 were female with age under 15 years. Neoplastic cases constituted around 72%, which included benign (2%) and malignant (98%) tumors. The spectrum include hematolymphoid neoplasms in 39.3%, small round cell tumors (SRCT) in 24.9%, Wilms tumor in 9.2%, germ cell tumors in 4.8%, spindle cell neoplasms in 4.8%, hepatoblastoma in 3.2%, and osteosarcoma in 3% of the cases. The metastatic lesions constituted 8.1% of the cases diagnosed by FNA.
CONCLUSION: FNA proves to be a reliable and efficien modality in diagnosing pediatric neoplasms in the hands of a skilled cytopathologist. Copyright:

INTRODUCTION

In India, 1.6%–4.8% of all cancer cases occur in children less than 15 years of age.[1] Among the various cancer detection methods, fine needle aspiration cytology (FNAC) plays a vital role in diagnosing pediatric malignancies. Though biopsy is said to be the gold standard for cancer tissue diagnosis, the utility of FNA in the pediatric age group is increasingly recognized in recent years due to various reasons. It is a minimally invasive procedure with low complication rates. It assures rapid diagnosis without subjecting the patients to anesthesia. It also proves to be a cost-effective diagnostic method with less turnaround time. This study evaluates the role of FNA in diagnosing neoplasms in children and enumerates the cytomorphological spectrum of childhood tumors. It also highlights the fact that FNA, when combined with ancillary studies, would enable a more specific diagnosis of pediatric malignancies.

MATERIALS AND METHODS

This retrospective study included 614 patients under the age of 15 years who underwent FNA during January 2015–december 2017 in our Institute. The cases were retrieved from the archives of the cytology division, pathology department. As it was a retrospective study and the identity of patients was not revealed in the study, ethics committee approval was not taken. FNA was done using 22–25 gauge needle for palpable lesions by the pathologist. A 21–25 gauge needle was used for deep-seated lesions by the pathologist for performing FNA under ultrasound guidance (USG). Direct smears were prepared which included wet fixed smears stained with Papanicolaou stain and air-dried smears stained with May-Grunwald Giemsa (MGG) stain. The remaining material was processed for cell blocks. For cell block preparation, the material in the syringe was fixed using 10% neutral buffered formalin, centrifuged, and the sediment was packed with 3% agar and subjected to histopathological processing. Special stains like Ziehl Neelsen for acid-fast bacilli w done whenever needed. Immunohistochemistry (IHC) on cell block was also done when indicated using avidin-biotin peroxidase method. For cytogenetic analysis, the FNA material was cultured in RPMI 1640 medium supplemented with fetal bovine serum and harvested, and slides were prepared. Giemsa-Trypsin-Giemsa banding procedure was followed. Histopathological correlation was done wherever available. Fluorescence in-situ hybridization (FISH) to detect Ewing sarcoma breakpoint region 1 (EWSR1) translocation was carried on the cell block and FNA material in five cases. The EWSR1 (22q12) Break Apart Probe Kit consists of a mixture of two FISH DNA probes. The first probe, a ~500 kb probe labelled in Spectrum Orange, flank the 5′ side of the EWSR1 gene and extends inward into intron 4. The second probe, a ~ 1100 kb probe labeled in Spectrum Green, flanks the 3′ side of the EWSR1 gene. The test was interpreted positively when more than 10% of the nuclei showed split or fused signals. Statistical analysis was done using SPSS software. Descriptive analysis of the data was performed. The continuous variables were presented as mean and range. The categorical variables were presented as percentages.

RESULTS

Aspirates in children constituted around 3.5% of the total FNA during the study period. Of the 614 cases, 336 were male and 278 were female. The age of the patients ranged from 1 month to 14 years. The cases were classified into four age groups <1 Yr, 1–5 yrs, 6–10 yrs, and 11–14 yrs with 1–5 years being the most common age group. Head and neck lesions (35%) were the commonest site for aspiration followed by the abdomen (30%), lower extremity (22%), chest (8%), and upper extremity (5%). USG aspiration was performed in 57.7% of cases. Cervical lymphadenopathy comprising around 25% of the cases was the commonest indication for FNA. Non-neoplastic cases constituted around 23%, whereas neoplastic cases accounted for 72% of the total cases. In 5% of the cases, the FNA smears were inadequate/unsatisfactory for a definitive opinion.

Among the non-neoplastic lesions, the majority cases were diagnosed as reactive lymphadenitis (57%) followed by granulomatous lymphadenitis (16%) and suppurative lymphadenitis (20%). Among the granulomatous lymphadenitis, five cases were positive for acid-fast bacilli by Ziehl Neelsen staining method. There were two cases of chronic sialadenitis, one case of adenomatous hyperplasia of the thyroid, and one case of Hashimoto's thyroiditis.

The neoplastic lesions were benign in (10/443) 2.2% and malignant in 97.7% (433/443) of the cases. [Table 1] Among the benign tumors, there were two cases of fibroadenoma, three cases of pleomorphic adenoma, one case of schwannoma, two cases of benign vascular lesion, and two cases of lipoma.

Table 1

Spectrum of cases diagnosed on cytology

Spectrum	No of cases
1. Hematolymphoid neoplasms	170/433 (39.3%)
a. Non Hodgkin lymphoma	102/170 (60%)
b. Leukemic infiltration	41/170 (24.1%)
c. Hodgkin lymphoma	27/170 (15.9%)
2. Small round cell tumor	108/433 (24.9%)
a. Ewing sarcoma	37/108 (34.3%)
b. Neuroblastoma	34/108 (31.4%)
c. Rhabdomyosarcoma	12/108 (11.1%)
d. Not categorized	19 (17.6%)
3. Wilm’s tumor	40 (9.2%)
4. Germ cell tumors	21 (4.8%)
5. Spindle cell tumors	21 (4.8%)
6. Hepatoblastoma	14 (3.2%)
6. Osteosarcoma	10 (2.3%)
7. Giant cell tumor of bone	2
8. Langerhans cell histiocytosis	3
9. Chordoma	1
10. Clear cell sarcoma of kidney	3
11. Mucoepidermoid carcinoma	2
12. Synovial sarcoma	1

The hematolymphoid neoplasms were the most common malignancy comprising around 39.3% (170/433) of the malignant tumors. They were further subtyped into non-Hodgkin lymphoma in 60% (102/170), leukemic infiltration in 24.1% (41/170), and Hodgkin lymphoma in 15.9% (27/170) of the cases. Among Non-Hodgkin lymphoma, there were 75.5% (77/102) cases of lymphoblastic lymphoma, 15.7% (16/102) cases of Burkitt lymphoma, 6.9% (7/102) cases of anaplastic large cell lymphoma (ALCL), and 2% (2/102) cases of diffuse large B-cell lymphoma (DLBCL). The smears of lymphoblastic lymphoma cases showed a monomorphous population of intermediate-sized immature lymphoid cells with high mitotic activity. The sub-categorization was done on biopsy in most cases. In a few cases of mediastinal non-Hodgkin lymphoma (NHL), due to difficulty in obtaining biopsy material from the mediastinal region, cell block was done with immunohistochemistry for categorization. Smears of Burkitt lymphoma had a starry sky pattern with malignant lymphoid cells showing nuclei with coarse chromatin, deeply basophilic cytoplasm, and cytoplasmic vacuolations [Figure 1a and b]. In cases of Hodgkin lymphoma, the smears showed a polymorphous population comprising lymphocytes, eosinophils, plasma cells, histiocytes with scattered binucleate, and mononuclear Reed-Sternberg cells [Figure 2]. Granulomas were observed in some of these cases. The cases of ALCL had smears with scattered large cells having multi-lobated nuclei, horseshoe-shaped nuclei, and hallmark cells.

Figure 1

((a) Burkitt's lymphoma – smear shows malignant lymphoid cells with cytoplasmic vacuolations. MGG × 400. (b) Karyotyping of Burkitt's lymphoma shows classic translocation 46, XX, t (8;14) (q24; q32)

Figure 2

Hodgkin lymphoma – smear shows classical Reed Sternberg cells with a background of reactive lymphoid cells. MGG × 400

The next common neoplasm was the small round cell tumors (SRCT) constituting 24.9% (108/433) of the malignant cases. Among SRCT, there were 34 cases of neuroblastoma, 37 cases of Ewing sarcoma, and 12 cases of rhabdomyosarcoma. A total of 19 cases with small round cell morphology were poorly differentiated and could not be categorized as the material was not adequate for ancillary tests. The cases of neuroblastoma had hypercellular smears with small round cells with salt and pepper chromatin and nuclear molding. Rosette formation with neuropil was observed in some of the cases which were the characteristic findings for rendering a definitive diagnosis. The smears of Ewing sarcoma cases had a biphasic population with smaller darker cells with scant cytoplasm and larger cells with a moderate amount of cytoplasm with vacuolations [Figure 3a–e. The smears of rhabdomyosarcoma had varied morphology with small round cells as one of its components, whereas others like strap cells, spindle cells, rhabdomyoblasts with myxoid background were also observed.

Figure 3

(a) Ewing sarcoma – smear shows a cluster of small round tumor cells. MGG × 400. (b) Cell block section shows sheets and clusters of small round tumor cells. H and E × 100. (c) Tumor cells show strong membranous expression of CD99. IHC × 400. (d) Karyotyping shows classic translocation of Ewing sarcoma with additional numerical abnormalities. (e) Fluorescence in situ hybridization with EWSR1 gene translocation Breakapart probe shows interphase nuclei with one normal fusion signal and one split signal pattern indicating rearrangement of one copy of EWSR1 region

Wilms tumor constituted 9.2% (40/433) of cases. The classic triphasic morphological pattern comprising blastemal, epithelial, and mesenchymal elements was observed in most of the cases. Some of them had predominant blastemal element mimicking a small round cell tumor which were confirmed by correlating IHC on the cell block and radiological findings.

There were 21 cases of germ cell tumors constituting 4.8% [Figure 4d], and 21 cases of spindle cell tumors comprising 4.8% of the neoplastic cases. There were 14 cases of hepatoblastoma constituting around 3.2% of the neoplasms. Smears from these cases had tumor cells arranged in trabeculae and clusters, and few cases displayed lining with endothelial cells. All of them were of epithelial type [Figure 4c].

Figure 4

(a) Osteosarcoma – Smear shows an osteoid matrix with few tumor cells. MGG ×400. (b) clear cell sarcoma of kidney – smear shows polygonal tumor cells with wispy cytoplasm and nucleus with fine chromatin and focal nuclear grooves. Myxoid matrix with spindle cells is seen. PAP ×400. (c) Hepatoblastoma – smear shows epithelial component with polygonal tumor cells resembling fetal epithelial cells. PAP ×400. (d) Germ cell tumor – smear shows a cluster of tumor cells with vacuolations in cytoplasm and eosinophilic matrix material. MGG ×400

Among the bone tumors which constituted around 3.7% (16/433), there were 10 cases of osteosarcoma (2.3%), three cases of Langerhans cell histiocytosis, two cases of giant cell tumor, and one case of chordoma. Smears from cases of osteosarcoma showed a pleomorphic population of the spindle to polygonal cells with multinucleated tumor giant cells and eosinophilic osteoid-like matrix [Figure 4a].

There were three cases of clear cell sarcoma of the kidney [Figure 4b], two cases of mucoepidermoid carcinoma, and one case of synovial sarcoma.

The metastatic lesions constituted 8.1% of the cases diagnosed by FNA. The cytomorphological spectrum included small round cell tumors, Wilms tumor, nasopharyngeal carcinoma, germ cell tumor, and osteosarcoma.

Cellblock was done in 33% (143/433) of neoplastic cases. IHC on cell block was done in 13.62% (59/433) of the cases which helped in categorizing SRCT and in sub-typing a few mediastinal lymphoma cases. Cytogenetic study supported the diagnosis in 7.6% (33/433) of neoplastic cases. FISH to detect EWSR1 re-arrangement was done on cell block for four cases and on FNA material for one case with EWSR1 break-apart probe. Four out of five cases showed EWSR1 rearrangement complementing the diagnosis of Ewing sarcoma.

Histopathological correlation was available in 25.2% (109/433) of the neoplasms, among which concordant diagnosis was seen in 94.5% (103/109) of the cases. Cyto-histo discordance was observed in 5.5% (6/109) of the cases. Two cases of granulomatous lymphadenitis, one case each of inflammatory lesion, atypical lymphoid cells in CML, synovial sarcoma, Hodgkin lymphoma reported on FNAC turned out to be Hodgkin lymphoma, benign skin adnexal neoplasm, reactive lymph node, Ewing sarcoma, and metastatic undifferentiated carcinoma, respectively [Table 2].

Table 2

Cases with discordance in cyto-histo correlation

Cytodiagnosis	Histopathology diagnosis
1. granulomatous lymphadenitis (2 cases)	Hodgkin lymphoma
2. Inflammatory lesion	Benign adnexal neoplasm
3. Atypical lymphoid cells in a case of CML	Reactive lymph node
4. Synovial sarcoma	Ewing sarcoma
5. Hodgkin lymphoma	Metastatic undifferentiated carcinoma

DISCUSSION

Pediatric tumors are different from adult ones and show distinctive histology and biologic behavior. Though biopsy is considered to be the gold standard in diagnosing these tumors,

FNAC has many advantages over biopsy which include ease of performance, repeatability with no morbidity, and no risk of tumor upstaging.[234] The FNA material can be triaged and can be used for ancillary studies, which can enable a pathologist to give a specific diagnosis.

In the present study, cytohisto diagnostic concordance was high around 94.5%, which signifies the diagnostic ability of the FNA technique.

In this study, majority of the cases (34%) were in the age group of 1–5 years with male preponderance (55%), whereas in the study by Maheshwari et al.[5] majority of cases (40.82%) were in the age group of 11–14 years with male preponderance (66.67%). Our institute being a tertiary oncology center, the number of neoplastic cases was more compared with reactive/infectious conditions.

Head and neck region was the most common site for aspiration comprising around 35% of the cases and cervical lymphadenopathy constituting 25% was the commonest cause for aspiration. Prathima et al.[6] also reported in their study that cervical lymphadenopathy (48.3%) was the commonest cause for aspiration in pediatric patients. FNA plays a very important role in the assessment of lymphadenopathy in children.[7] It helps to avoid unwanted surgical excisions in reactive conditions and also document recurrence/relapse of primary hematopoietic malignancies or metastatic disease. In this study, the largest malignant group was lymphoma which comprised 39.3% of malignant cases and was similar to the study by Maheshwari et al.[5] where the authors also documented lymphoma as the largest malignant group comprising 25.1% of the cases. However, this was in contrast to the study by Kusumakumary et al.[8] who observed lymphoma to be the third most common malignancy.

FNAC has become an important modality in diagnosing SRCT.[910] SRCT constituted 24.9% and formed the second largest group in our study. Maheshwari et al. also reported similar findings in their study with 21.3% of the SRCT cases.[5]. Poorly differentiated tumors cannot be exactly categorized at the level of light microscopy.[11] Ancillary techniques such as immunohistochemistry, cytogenetics, and molecular genetics are required to diagnose those poorly differentiated tumors. In such cases, FNA yields an adequate number of dissociated viable cells making it suitable for ancillary techniques.[12] Thus, FNA obviates the need for biopsy which is a time-consuming procedure and also becomes a productive diagnostic tool for documenting primary and metastatic SRCT in pediatric cases. In this study, cytogenetics supported the diagnosis of Ewing sarcoma in 11 cases and neuroblastoma in 6 cases.

FNAC has a definite advantage over surgical excision biopsy to arrive at a tissue diagnosis before initiation of therapy. There are several studies demonstrating the usefulness of FNA in diagnosing pediatric renal tumors.[1314] It has already been documented that neither trucut biopsy nor FNA upstages pediatric renal tumors.[15] Using this rationale in our institute, FNA is done not only for those inoperable cases before starting preoperative chemotherapy but also inoperable cases to document diagnosis before surgery. In this study, we had 40 cases of Wilms tumor, most of which were diagnosed on cytomorphology alone. However, in few cases where there were only blastemal elements mimicking other small round cell tumors, we applied an immunohistochemistry panel on the cell block to confirm the diagnosis. WT1 positivity in the blastemal component helped us to arrive at the diagnosis. We also had two cases of clear cell sarcoma, the smears of which showed both cord cells which were polygonal with wispy cytoplasm and nucleus with fine chromatin and focal nuclear grooves and septal cells which were spindle-shaped with myxoid material in the background. These findings are similar to those described by Iyer et al.[16]

The role of FNA in diagnosing germ cell tumors in extragonadal sites such as retroperitoneum, mediastinum, liver, gluteal, and sacrococcygeal regions has been documented in the literature.[1718] In this study, there were 21 cases of germ cell tumor diagnosed on FNA at extragonadal sites. All these cases were correlated with the serum tumour markers.

Although rare, hepatoblastoma is the most common primary malignant neoplasm of liver occurring predominantly in infants and children younger than 3 years.[1920] In the present study hepatoblastoma constituted 3.2% of malignant neoplasms and were morphologically subtyped as epithelial type.

Among the soft tissue tumours spindle cell morphology was the most commonly observed. On FNA smears they could be categorised as benign spindle cell neoplasm/sarcoma. Exact categorisation could not be done in some cases due to low cellularity and the absence of tissue architecture. Dey et al.[21] in their study had expressed similar views on inability to categorise soft tissue tumours on FNA due to heterogeneity and diagnostic overlap between various histological subtypes of these soft tissue neoplasms.

In 5% of the cases, the smears were unsatisfactory and inadequate for definitive diagnosis. This may be due to the sampling error which was one of the few limitations of FNAC. The other causes included tumour characteristics like necrosis, cystic degeneration and fibrotic nature. This could be reduced by doing the aspiration under guidance and repeating the procedure when required with an experienced hand.

In our study there was discordance between cytodiagnosis and histodiagnosis in six cases. 2 cases of Hodgkin lymphoma which were diagnosed as granulomatous lymphadenitis on cytology and 1 case of benign skin adnexal neoplasm which was reported as inflammatory lesion on cytology were due to sampling error. In the other cases the discordance was due to the interpretation error. This could have been reduced by using ancillary studies like cell block, immunohistochemistry, cytogenetics and molecular studies.

To conclude, this study is a comprehensive one describing the spectrum of pediatric malignancies diagnosed on FNAC. It also emphasises the utility of ancillary studies which increases the diagnostic accuracy and reduces the need for biopsy in pediatric cases especially in those cases where neoadjuvant chemotherapy can be planned. Though there are few limitations, FNA proves to be a reliable and efficient diagnostic modality in the hands of a skilled cytopathologist.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.