FNAB of the thyroid is a very common procedure for the initial evaluation and diagnosis of thyroid lesions. It is a simple, safe, reliable and cost effective procedure as a first line technique for the diagnostic assessment and management of thyroid lesions. It is also a very popular out-patient clinical procedure that can be performed with or without ultrasound assistance depending on the size of the lesion [1
]. Usually, an average of three passes is performed and direct smears are made at the time of the procedure. Some of the smears are air-dried and stained with Diff-Quik stained, and others are alcohol-fixed (spray fixed) and stained with Papanicolaou stained. In addition, the remaining aspirate material from each pass is rinsed and flushed in cell preservative solution, such as Cytolyt Solution or Saccomano's fluid, or in saline. Traditionally, CB has been made from this rinsed material and Hematoxylin & Eosin stained slides are prepared in addition to the direct smears, as is done on FNAB of many other organs, like the lung, liver and pancreas. However, during the last decade liquid-based monolayer slide preparation such as the TP method has gained widespread acceptance in the non-gyn cytology practice after a tremendous success in the gyn Pap test cytology [6
]. As a result, many cytology labs have converted to TP slides preparation from the rinsed aspirate instead of the usual CB preparation. Some laboratories have even elected to make only TP slides without conventional smears or CB slides, especially with thyroid FNAB specimens obtained in physician offices.
There have been several studies comparing the utility and advantages of TP method and the conventional direct smear method in thyroid FNAB samples [12
]. Fewer studies, however, were conducted to compare the utility and advantages of TP slide method with that of CB slides in thyroid FNAB specimens [3
]. A study by Selvaggi and Sanchez found that the contribution of the CBs in the diagnosis of thyroid lesions is minimal because of low cellularity [3
]. They also found that the CBs were not helpful in the majority of cases and were contributory in only 31% of all 82 cases that had CB preparation. More importantly, CBs were contributory in only 5 of 23 (21.7%) of neoplastic thyroid lesions. Another study by Siddiqui et. al. of 197 thyroid FNAB cases found that the majority (57.9%) of cases were diagnosed only on conventional smears, either Diff-Quik or Papanicolaou stained [4
]. The authors also found that CB slides were diagnostic only in 6.1% of the cases.
In our study, we found that TP slides are much more likely to be diagnostic of colloid nodules, colloid nodules with cyst, chronic thyroiditis and atypical/neoplastic lesions than CB slides. Overall, TP slides were diagnostic of various thyroid lesions in 86/126 (68%) of the cases, while CB slides were diagnostic in only 31/128 (24%) of the cases. The CB and TP slides had similar diagnostic yield only in cases of degenerative thyroid cysts, 17/128 (13%) vs. 16/126 (13%), respectively. In cases of colloid nodules or colloid nodules with cystic change, CB had diagnostic yield of 10/128 (8%) compared to 52/126 (41%) on TP slides. We also found that CB slides were diagnostic of chronic thyroiditis in only 4/128 (3%), while TP slides were diagnostic in 14/126 (11%). More significantly, we found that 5 CB slides failed to identify atypical/neoplastic lesions, including 2 follicular neoplasms that were diagnosed on the corresponding smears. On the other hand, 4 TP slides detected atypical/neoplastic lesions, including 1 papillary carcinoma, that were also diagnosed on the corresponding smears. This sharp contrast is perhaps the most important finding in our study showing that TP slides are more likely to detect atypical/neoplastic lesions than CB slides in thyroid FNAB cytologic evaluation.
Our results are essentially in agreement with those of previous studies which demonstrated good diagnostic yield of TP slides of thyroid aspirates. Frost et al found that TP slides of thyroid aspirates have an 85% diagnostic accuracy, and that preparation of only two TP slides is sufficient for accurate cytologic interpretation [15
]. Yet, in a recent study [23
] by Hasteh and Pang, they found that only one TP slide is representative of the specimen and is sufficient to make an accurate diagnosis. Irizar et al in their investigation reported that TP slides improve the diagnostic accuracy of thyroid FNAB samples. On the other hand, Biscotti et al found that TP slides offer similar diagnostic accuracy to that of conventional smear preparations [11
A major advantage of CB preparation is the ability of performing special stains or immunocytochemical stains if needed [18
]. This has been very helpful in FNAB of other organs especially the liver to differentiate metastatic tumors from primary liver carcinoma. However, there have been recent studies demonstrating the ability of performing immunocytochemical stains on TP slides, including those of the thyroid FNAB, with very good results [10
]. A recent study by Rossi et al regarding immunocytochemical stains evaluation of thyroid neoplasms on TP slides from thyroid FNAB revealed that combining the cytomorphology with the immunocytochemical stain panel of HBME-1, Galectin-3 and RET was effective in distinguishing follicular lesions requiring surgery from those lesions requiring only follow-up [24
]. However, the results obtained with this approach have not been directly compared with same specimens processed by traditional method on CB material.
Some authors have also elaborated on the cytologic features of specific thyroid lesions, such as follicular lesions and papillary carcinoma, on TP slides of thyroid FNAB specimens and described the differences from the features seen on traditional smears or CB slides [26
In summary, we conclude that TP slide preparation in thyroid FNAB is more useful than CB slide preparation. Our study shows that the diagnostic yield of TP slides is at least twice that of CB slides in detecting thyroid lesions on FNAB, including atypical/neoplastic lesions, except for degenerative cysts. We further believe that TP slides should be made in addition to but not in lieu of direct (Diff-Quik and Papanicolaou stained) smears as they complement each other.