A study of squash smear cytology in the diagnosis of non-glial lesions in GMKMCH, Salem

Introduction

The lesions of central nervous system are varied. The incidence of brain tumors in India is approximately 5 - 10 per 1,00,000 people.1 Glial tumors are among the commonly encountered intra-cranial lesions which comprises about 40.3% of all brain tumors.2 The non-glial lesions include a broad spectrum of conditions like meningioma, schwannoma, small round blue cell tumors and metastasis. Due to the infrequent incidence of these conditions, the knowledge of smear study in case of Non-glial lesions remains less explored. It is further difficult when the amount of biopsy material received is small.

Squash cytology is a rapid, inexpensive and effective method with an accuracy rate of 95%.2 It requires only a minimal amount of tissue for diagnosis which is uplifts the paramount importance of squash cytology because resection of even a tiny tissue from functionally significant areas of brain is cumbersome.3 Thus, it serves as a useful first line modality in directing the neurosurgeon towards appropriate management.4, 5, 6, 7 Also, it can be particularly useful in a resource limited setup wherein frozen sections cost more.8 The method of making a smear is comparatively easier and can be stained by usual staining protocols. Kumaraguru et al considered squash cytology to be mirror image of histopathology.9 However, detailed knowledge about smears of various CNS lesions is crucial in making a diagnosis.

This study aims to provide a detailed discussion about the squash cytology of various Non-Glial lesions encountered in our hospital and their distribution according to age and gender which will lead to better diagnostic conclusions and effective managements.

Aim and Objectives

Materials and Methods

It is a retrospective study from November 2019 to November 2021, over a period of two years. A total of 30 cases were included in this study. Samples were obtained from Department of Neuro Surgery as fresh specimen. The labelled specimens were received and given an unique accession number. A tiny portion of the tissue was held between two clean glass slides and the tissue was crushed. The slides were moved in opposite directions to smear the tissue. The smears were immediately fixed in absolute alcohol solution. After 15 minutes, the slides were stained with Hematoxylin and Eosin staining method. The cytological features of the cases were studied and diagnosed. The remaining tissue was fixed with 10% neutral buffered formalin, processed and stained with Hematoxylin and Eosin stains. The cytological diagnosis was then confirmed with histopathological diagnosis.

Distribution of cases

In our study, meningioma was the most commonly occurring Non-Glial lesions, followed by schwannomas. The total number of meningiomas studied was 12 which is double the number of schwannomas. The accuracy rate of diagnosing the lesions by squash cytology is 93.3%.

Figure 1

Showing epitheloid cell clusters in a fibrillary background- Tuberculous abscess (40x view)

Figure 2

Showing whorls of meningothelial cells with focus of psammamatous calcification – Meningioma (40x view)

Figure 3

Showing intranuclear inclusions in meningothelial cells – Meningioma (40x view)

Figure 4

Showing cohesive sheets of spindle cells – Schwannoma (10x view)

Figure 5

Showing cells with scant cytoplasm and hyperchromatic nuclei- (Medulloblastoma- 40x view)

Figure 6

Showing clusters and singly scattered polygonal cells with moderate cytoplasm with pleomorphic vesicular nuclei and coarse chromatin- Metastatic squamous cell carcinoma deposits (40x view)

Figure 7

Showing melanin pigments in malignant cells- Metastatic melanoma (40x view)

Discussion

The present study was conducted from November 2019 to November 2021 over a period of 2 years. Though various studies have been made in this subject, Jindal et al. suggested that it is necessary to know the essential clinical history and radiological imaging before smear evaluation.10 Squash cytology of Non-Glial lesions of a total of 30 cases was studied. The commonly affected age group was 51-60 years. This was similar to a study conducted by Seema Acharya et al,11, 12 and Kaki et al.13 Also, the majority of the patients were adults rather than elderly patients and children. Dogar et al,14 Deshpande et al15 and Goyani et al16 showed that majority of the cases were observed in fourth decade.

Among the 30 cases studied, there was a slight female preponderance in the distribution of cases. Although a study conducted by Deorah et al17 suggests that males are at higher risk in procuring brain tumours than females due to the difference in susceptibility of X and Y chromosomes to the tumour stimuli, the recent WHO classification states that most of the Non-Glial lesions like meningiomas and schwannomas occur commonly in females rather than males.18

The distribution of lesions in our study showed frontal lobe as the common location of majority of tumours. It was followed by cerebellopontine angle where nearly all of the tumours encountered were Schwannomas. One case of temporal abscess was seen which turned out to be a case of Aspergillosis. Both the cases seen in cerebellum turned out to be Medulloblastomas. Fronto-temporal was reported to be the common site by a study conducted by Nanarng et al19 wheareas parietal region was the commonest in studies done by Kaki et al,13 Goyani et al16 and Dogar et al.14

The accuracy rate of Squash cytology with comparison to the final histopathology was 93.5%. The sensitivity and specificity were 96.5% and 98.7% respectively. This proves the utility of squash smear cytology in diagnosing CNS lesions. Chart 4 compares the number of cases diagnosed by squash cytology and their corresponding histopathological analysis.

In our study, one case of meningioma was misdiagnosed as metastatic adenocarcinomatous deposits. This is because of the absence of whorls and psammoma bodies which are the characteristic features of meningiomas. However, it is a commonly encountered pitfall which could be overcome by correct smearing techniques and the identification of broad fibers connecting meningothelial cells.20 Studies done by de Souza Balsimelli et al21 and Mitra et al22 encountered similar diagnostic pitfalls and have suggested solutions to avoid them.

Fungal infections of CNS can occur in immunocompromised individuals, masquerading as mass lesions in radiology. Clinical history and MRI findings are crucial before attempting to diagnose a case of CNS infection. The presence of plasma cell rich infiltrates along with ill-defined granulomas and fungal hyphae helped in the diagnosis of two cases in a report published by Parth A. Desai et al.12 In our study, definitive fungal hyphal elements were not seen and hence the case was reported as inflammatory smears. The sensitivity, specificity and accuracy of squash cytology in diagnosing specific lesions in our study were as follows:

The results of our study were similar to that of a study done by Seema Acharya et al.11 The accuracy rates of the study in diagnosing meningiomas, schwannomas, pituitary adenomas, epidermoid cysts and metastasis were 95.1%, 100%, 100%, 100% and 81.8% respectively.

Conclusion

Squash cytology proves to an effective and rapid technique for the typing of Non-glial lesions. Meningioma is the most common tumor followed by schwannoma. Males are more commonly affected than females. The common age group affected was middle-aged adults. Squash cytology proves to be an effective alternative for histopathology. In our study, the diagnostic accuracy of CNS smears in comparison to histopathology is 93.75%.

Source of Funding

None.

Conflict of Interest

None.