Smear technique for intraoperative diagnosis of central nervous system neoplasms

Correspondence: Dr. Srijana Shrestha, MD Consultant pathologist, Grande City Clinic and Diagnostic Services, Jamal, Kathmandu, Nepal E-mail: srijanak82@gmail.com Background: Smear cytology has become increasily popular as an alternative to frozen section for the rapid diagnosis of most of central nervous system lesions. The aim of this study was to assess the utility of smear technique for the rapid diagnosis in the neurosurgical biopsies and to compare the smear cytological features with the final histopathological examination.

technique is superior in displaying abnormal cellularity, nuclear and cytoplasmic details and occasionally even tissue architecture. 1,2  of smear technique safeguards the surgeon being in the wrong location, prevent sampling purely necrotic or reactive tissue, thereby avoiding a need for second anesthesia and invasive procedure.In cases of radical excision of diffusely infiltrating gliomas where margins are not obvious macroscopically, the intraoperative smear technique can be useful to define the margins. 37 Smear technique requires a very small amount of tissue, as small as 0.1cm for its preparation.With increase use of stereotactic technique in neurosurgical field, there is limitation of size if biopsy which might be inadequate for other technique such as frozen section.6]

MATERIALS AND METHODS
This was a prospective interventional study conducted in BPKM Cancer Hospital for a period of one year.It included 60 consecutives cases that underwent for open craniotomy and burr hole biopsy in the neurosurgical department.The biopsy samples were transferred in isotonic saline.Smears were prepared by placing 1-2 mm of biopsy material on at one edge of a clean, dry and labeled slide and crushing with another slide with just enough pressure to spread the tissue into a thin film.The smear was immediately immersed in 95% ethanol and stained with Papaniculaou stain.Remaining biopsy was submitted for paraffin sections.Cytological features were studied in detail, radiological and operative findings were compared with cytological findings.All Smear cytological diagnoses were compared with histological findings.The tumors were classified according to the World Health Organization Classification of CNS.

RESULTS
Overall diagnostic accuracy of smear technique for rapid diagnosis achieved in the present study was 88%.Complete correlation was considered for the cases in which the intraoperative cytological diagnosis was same as the histological diagnosis including the grading.Total discrepancy between cytological and histological diagnosis was in five cases (Table 1).The misdiagnosis in cytology were mainly due to sampling error and the lack of histological architecture.Four cases of gliomas showed partial discrepancy.Partial Discrepancy was considered for the cases where the grading of the tumor not same in cytology and histology diagnosis.In a total of 60 cases, Gliomas (51.6%) were the most frequently occurring tumor (Table 2).

DISCUSSION
Inherent soft nature of CNS tissue of brain tissue and high water content renders poor quality frozen sections.A cytological examination has shown to be great value as an alternative method in intraoperative consultation of CNS pathology.Intraoperative consultation of brain lesions are requested to differentiate neoplastic from reactive lesions; to differentiate metastatic from primary lesions; to estimate the degree of malignancy and to determine the tumor margins. 7,80][11] Most of the gliomas were easily identified in the smears.Presence of Fibrillary background in smear were very useful features to diagnose gliomas (fig. 1) .Regarding grading of tumor in smear, Marshall et al have mentioned in his study that the high grade tumors are liable to undergraded in smear because necrotic tissue which is of the hallmark for high grade tumor in histology would be purposely avoided when selecting the small portion of biopsy to be smeared. 12n the present study, four cases were undergraded due to lack of all the features.As Gliomas could be heterogeneous, many studies have also concluded that it would be unwise to grade the tumors in every cases in rapid diagnosis. 1,7,10,12 the study conducted by Jennifer et al, the most common and distinctive findings in 23 cases of pilocytic astrocytoma were markedly elongated bipolar cells, Rosenthal fibers and eosinophillic granular bodies. 13All these features were evident in our case of pilocytic astrocytoma (fig.2).
Similarly, cytological features of Oligodendrogliomas were very distinct in our cases as in the study of Roessler K et al. 14 Tumor cells were moderately pleomorphic, rather in monolayer sheets, well spreaded, with uniform oval nuclei and conspicuous nucleoli (fig.3).But, histological features such as perinucler halos and chicken wire like vascular channels were not evident in the smear. 10 Two cases of ependymoma were correctly diagnosed in the smear (fig.4).Poorly formed rosettes, mildly pleomorphic glial cells and calcifications were evident in the smears .In contrast to present study; Sidawy et al felt difficulty in distinguishing Ependymoma.The author emphasized the importance of definitive diagnosis of ependymoma, because a surgeon will try to go for complete resection in case of Ependymoma whereas in Diffuse Astrocytoma, surgery usually is terminated in favor of radiotherapy. 10,11sinterpretation of Glioblastoma as metastatic tumor was seen in one case due to presence of bizarre cells, the lack of fibrillary background and lack of architecture.Similar error was encountered in the study of Mouriquand et al.In our study, Out of Seven metastatic lesion, one case of the metastatic tumor was misdiagnosed as Glioblastoma due to presence of abundant gliofibrillary background in the smear. 8,9 h case of Hemagioblastoma and lymphoma and two cases of pituitary adenoma were easily identified in the smear.Discohesive round cells lying discretely in absence of fibrillary background with presence of lymph granular bodies in toluidine blue stain were the features of lymphoma.Pituitary adenoma showed cellular smear consist of round cells with salt and pepper chromatin (fig.5).Meticulous correlation with clinical and radiological features helped to achieve high accuracy in the present study.
Meningiomas were the second most common tumors in our studies (fig.6).In Most of the cases, meningothelial cells were easily identifiable.Meningothelial cells were oval to      round containing vesicular nuclei with conspicuous nucleoli and ill defined wispy cytoplasm.Psammoma bodies, whirling pattern, microcalcification, intracytoplasmic inclusions were readily appreciated in the smears as mentioned in the study of Kobayashi S et al.Two cases of atypical Meningioma were misinterpretated as low grade gliomas due to hyperchromatic irregular cells and prominent fibrillary in the background. 15

CONCLUSION
The current study also found smear /squash technique to be accurate and reliable for the rapid diagnosis of CNS tumors.It is highly recommended technique and can be safely practiced as an alternative to frozen sections.Lastly, the goal of the pathologist while using this technique in intraoperative set up is to give sufficient preliminary information to optimize the surgery.