Diagnostic Utility of CUSA Specimen in Histopathological Evaluation of Tumors of Central Nervous System
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.304072
Source of Support: None, Conflict of Interest: None
Keywords: Artefact, CUSA, diagnostic utility, histopathology, sampling
CUSA, Cavitron Ultrasonic Surgical Aspirator has been utilized as a method to decompress brain tumors since the early 1980s. It works by disrupting the tissue using high frequency ultrasound waves followed by aspiration, which clears the operating field of tissue and blood. Simultaneous irrigation with normal saline helps prevent heat related damage to surrounding tissue. The advantage of utilizing CUSA in neurosurgical practice, is that it facilitates removal of tumor without traction or manipulation. CUSA can also be used to demarcate the boundary between visually abnormal tissue and normal white and grey matter. Coagulation which is also used as a method of tumor decompression causes residual tissue which has to be removed secondarily. Coagulation also results in tissue damage which prevents histopathological assessment of the tissue.
Accuracy in histopathological diagnosis and grading is highly dependent on adequacy of tissue sampling as brain tumors are known to be heterogenous with regions showing high and low-grade areas. Sampling bias occurs due to several reasons. Surgical bias occurs when the surgeon removes tissue for histopathologic examination. As tumors are known to be heterogenous, the tissue sample sent for histopathologic evaluation may not represent a high grade focal area of the tumor. High grade areas tend to be very friable and are difficult to grasp with forceps. Also, presence of suction at the tumor site may result in removal of the high grade region and preferentially a low grade component would be sent for histopathologic analysis. A routine biopsy sample is usually of less than 1 cm3 volume. Most tumors which require operative intervention are greater than 3 to 4 cm in maximum dimension. Sampling bias is introduced both at the level of the operating neurosurgeon as well as the pathologist which has a direct bearing on accuracy of histopathological grading which is critical for patient management and therapeutic decisions. The neurosurgeon invariably does not submit all the tissue removed for histopathology. The CUSA specimen and the contents of the suction bottle are often not sent for histopathological analysis as a routine in most centers. However, inclusion of these specimens would greatly enhance the tissue available for histopathologic analysis and would improve diagnostic yield and accuracy.
But, these samples (CUSA and suction bottle) are subjected to mechanical damage during the surgical procedure. The ultrasonic waves, the force of suction applied while removing the tumor, and the shearing effect on tissues while passing into the receiving bottle, would produce alterations in morphology. The extent of these effects on the final diagnosis needs to be ascertained. Limited studies have evaluated the utility of CUSA samples for diagnosis, as well as for in vitro cell culture and detection of oncogene amplifications.,
In this study, we evaluated histological diagnosis on samples obtained from the CUSA bottle and compared with the gold standard of conventional specimens. The present study ascertained the utility of CUSA in the histopathological evaluation of CNS tumors.
All the tissue samples in which CUSA was used intraoperatively to decompress tumor tissue in the Department of Neurosurgery, NIMHANS from 2013 to 2017 were included in the study. The surgical team had a standardized policy on the use of CUSA as described below.
All intra-axial tumors irrespective of their operative impression; whether high grade or low grade were decompressed using CUSA. CUSA was used to decompress several extra-axial tumors as well. In case of extra-axial tumors, capsular dissection was also adopted along with CUSA based decompression. All surgeries were performed by using the Soering Sonoca CUSA machine. The handpiece used had an external diameter of 2.3 mm. In the case of intra-axial tumors, low intensity CUSA technique was used as a uniform policy. The ultrasound intensity was set at 20%, with aspiration set at 27 barr and irrigation set at 7 ml/min. In the case of extra-axial tumors such as vestibular schwannoma and meningioma, a maximum ultrasound of 75% (corresponding to Setting 3 of the machine) was used.
Conventional tissue specimens were also obtained in 47/73 cases. Only in cases where the tumor was located deep and corridor access was minimal, CUSA based specimens alone were available. All the specimens were subjected to fixation in 10% neutral buffered formalin and processed for paraffin embedding. The hematoxylin and eosin stained sections were evaluated with respect to cellularity, cytomorphology, architecture, background, vasculature, mitosis, necrosis and alterations in morphology, induced by CUSA/suction and its effect on diagnosis. All the above-mentioned features were studied in the CUSA as well as conventional tissue sections (wherever available) and were compared. The analysis was done with respect to individual parameters and the overall diagnostic utility of the specimen.
Total of 73 cases were included in the study. Conventional biopsies were available for comparison in 47 cases. In 26 cases, CUSA samples were the only material available. The categories of tumor studied included Gliomas, Medulloblastomas, Schwannomas, Meningiomas, and metastasis.
Twenty-eight gliomas comprising 11 glioblastoma (GBM), 2 gliosarcoma, 6 oligodendroglioma, 3 astrocytoma, 1 pilocytic astrocytoma, and 5 mixed gliomas were included in the study. Cellularity, cytomorphology, and architecture were as well represented in CUSA as in the conventional specimen. Astrocytoma/oligodendroglioma typing could be made on CUSA specimen. In two of the oligodendroglioma, classical features including calcification was also detectable in CUSA specimen. Astrocytic and oligodendroglial components of the mixed gliomas were seen in both the conventional as well as the CUSA specimen. The major disadvantage with CUSA specimens in gliomas was with respect to detecting necrosis and mitotic activity, essential for grading of gliomas. These features were better appreciated in conventional biopsy sections compared to CUSA. Artefactual hemorrhage, necrosis, and fibrinous debris were seen in CUSA, which interfered with interpretation. However, in one of the cases of GBM, the tumor was better represented in CUSA than in conventional section which included normal and infiltrating area of the brain parenchyma in contrast to the CUSA specimen which had majority of the tumor. In 9 out of 28 gliomas studied, the grading on CUSA was lower than on the conventional sections [Figure 1]a, [Figure 1]b. Immunohistochemistry results however were optimal with CUSA tissue, wherever performed.
Sarcomatous component of gliosarcoma was identified in one each of the conventional biopsy tissue and CUSA included in the study [Figure 1]c, [Figure 1]d. The case of pilocytic astrocytoma was diagnostic in CUSA.
There were three cases of ependymoma, all of them were equally represented and diagnostic in CUSA as compared to the conventional section. Characteristic perivascular pseudorosettes were noted.
There were three cases of meningioma. One of them was an atypical meningioma, which could not be accurately graded on CUSA, due to difficulty in identifying sheeting pattern and mitotic activity in the CUSA specimen [Figure 2]a, [Figure 2]b. A case of metaplastic meningioma was included. The metaplastic component (ossification) and brain invasion by the tumor was not represented on CUSA section. The other case was a rhabdoid meningioma which was diagnosed on CUSA as well as the conventional biopsy sections.
Eighteen schwannomas with only CUSA specimen were found to be diagnostic with spindle shaped cells arranged in fascicles and exhibiting nuclear palisades. Two schwannomas, where CUSA and conventional specimen were available were equally representative.
Two cases of metastasis could be diagnosed on CUSA. They had tumor cells arranged in nests, with round to polygonal cells exhibiting pleomorphism and mitosis.
Nine cases of medulloblastomas were included in the study. All the cases showed presence of crushed cells and necrotic foci as an artefact induced by CUSA. Histological subtyping of medulloblastomas and appreciation of cytomorphology was affected in CUSA sections [Figure 2]c, [Figure 2]d. In a single case of anaplastic medulloblastoma, features of anaplasia were appreciated in the conventional sections, but could not be observed on CUSA. Medulloblastomas could be diagnosed on CUSA but subtyping was difficult. Artefacts were prominent.
Single case of craniopharyngioma was diagnostic on CUSA.
Common artefacts noted on CUSA specimen as a result of aspiration were necrosis-like foci, hemorrhage and artefactual empty spaces in the sections [Figure 3]. Cellular tumors showed significant crush artefacts.
CUSA, as a technique for operating the CNS tumors is being employed widely in current neurosurgical practice. In this study, we have analyzed the alterations induced by the ultrasonic fragmentation at the histological and cytological level and also attempted to determine the diagnostic utility of tissue obtained from CUSA in comparison to the conventional biopsy/resection specimen.
As the technique allows the surgeon to selectively resect the tumor without causing much distortion of the surrounding normal brain parenchyma, this procedure is advantageous. From the pathologist's perspective, the artefacts induced by CUSA do result in distortion of morphology at cellular level. But, as the technique allows obtaining tissue from multiple areas of the tumor, in contrast to the conventional biopsy, it is probably more representative of the entire tumor, provided the entire sample is processed.
Distortion caused by CUSA affects tumors that are more cellular (small round cell tumors) and which have less stroma/matrix (gliomas) in contrast to fibrous/firm tumors like metastasis/schwannoma where there is minimal/negligible differences between the tissues obtained by the two techniques.
In our study, we have observed that the diagnostic utility of CUSA is comparable to the conventional tissue in tumors such as schwannoma, metastases where grading is not a component of assessment. In conventional, non-syndromic schwannomas identification of classical architecture is diagnostic. In the other most common mesenchymal tumor, meningioma, CUSA allows diagnosis, though grading accuracy is hindered as parameters such as brain invasion and identification of mitosis are better represented on conventional tissue sections.
In gliomas, though subtyping of the tumor as astrocytoma or oligodendroglioma is not affected by the type of tissue submitted, grading of the tumor gets affected when CUSA sample alone is submitted for examination (mainly due to artefacts). CUSA specimen examined in conjunction with conventional specimen, greatly enhances the diagnostic yield due to wider sampling, in addition to surgical advantage.
In cellular, small round cell tumors such as medulloblastoma, the cytology is markedly distorted due to smearing of fragile DNA in rapidly multiplying cells (Azzopardi phenomenon). Currently, although molecular subtyping has been introduced in the classification of medulloblastoma, it is known that histo-molecular subtyping is essential for prognostication. Hence histological subtyping of medulloblastomas is vital, which requires examination of conventional tissue sections.
Earlier studies have analyzed the utility of CUSA specimen for diagnosis of CNS tumors.,,,,,, In the first study by Blackie et al., the best preservation of morphology was noted with neurilemmomas, meningiomas, and metastatic carcinomas, similar to our study. Minor histological distortion was observed with respect to glioma samples.
Silvermann et al. evaluated the cytomorphologic appearances of 22 central nervous system tumors in CUSA samples and compared with the findings in biopsy or resection specimens. They recommended that CUSA tissue could be used to prepare cell block and cytologic smears.
Finley JL et al. studied eleven cases of meningioma, three cases of glioblastoma, one astrocytoma, and two schwannomas and evaluated the utility of CUSA tissue for immunocytochemistry. They concluded that reliable morphologic and immunoperoxidase studies can be performed on cytologic material obtained by the CUSA, which could aid in making an accurate and specific diagnosis of a variety of CNS tumors. Utility of CUSA tissue for flow cytometry and in-vitro cell culture studies has also been reported.,,
The highest utility would be in two scenarios. One in which the diagnosis is difficult from a small amount of tissue, the CUSA sample would provide a larger volume which can be sampled. The second is in grade II gliomas where isolated small foci with high grade areas may be present. The CUSA sample reduces the sample bias and has the potential of bringing to notice high grade areas within a low-grade glioma.
CUSA samples submitted for histopathology, when analyzed with conventional samples improve the diagnostic accuracy. In non-glial tumors (mainly mesenchymal tumors), the diagnostic utility of CUSA samples is comparable to the conventional samples. However, there is a limitation with respect to grading of glial tumors utilizing CUSA samples alone. Thus, in gliomas, examination of both conventional as well as CUSA samples is essential for accurate characterization and grading. In case of medulloblastomas, it is mandatory to submit and examine conventional tissue samples for histological subtyping of medulloblastomas. As a surgical policy, it would be beneficial that all removed tissue samples including those from the CUSA bottle and suction be sent for analysis. The additional tissue would be essential in cases where the histopathological grading is critical for patient management. Additionally, in sites, where obtaining conventional biopsy poses a major risk, CUSA forms an ideal alternative, keeping in mind the limitations discussed in the study. Technologies such as digital histopathology, molecular analysis are developing at a rapid pace. One of the major advantages of these technologies involves rapid processing of large amount of tissue samples. In such a context, it is only fair that the entire operative specimen is available for histopathologic analysis.
The authors wish to acknowledge the assistance of Mrs. Hemavathy U, Chief Technician, Department of Neuropathology, NIMHANS, Bengaluru in performing immunohistochemistry and Mr. Manjunath K, Department of Neuropathology, NIMHANS, Bengaluru for photographic montages.
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Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3]