We read with interest the recently published article by Fakhry et al. studying the use of fine needle aspiration cytology (FNAC) and frozen section in the diagnosis of malignant parotid tumours, and would like to make further comment.
Parotid lesions should undergo triple assessment; namely clinical examination, imaging, and then confirmation of pathology with some form of biopsy. The authors state that magnetic resonance imaging (MRI) is the standard imaging method for parotid tumour diagnosis. In current practice, ultrasound is increasingly accepted as the initial imaging modality of choice for parotid assessment, and has shown itself to be highly accurate in parotid lesion characterization and diagnosis. Ultrasound acts as a guide for the need to further imaging, usually MRI, for larger, deep lobe or likely malignant lesions, and can be used to guide needle biopsy.
Biopsy confirmation of lesion histology is critical; an accurate diagnosis allows correct selection and timing of operative intervention, it facilitates the use of parotid sparing surgery if appropriate, informed patient consent can be obtained (facial nerve injury), and surgery can be avoided in some patient groups (elderly, unfit) and tumours (Warthin’s).
The authors discuss the use of a combination of FNAC and frozen section in managing parotid tumours. In their series, a correct diagnosis was obtained with FNAC in 116/138 cases (84%) with 8 false-negative and 14 false-positive results. Frozen section did perform better, with a correct diagnosis in 130/138 cases (94%). FNAC was performed in relatively optimized circumstances by a cytologist, with the opportunity to repeat sampling. These results support existing published data, suggesting that FNAC often performs poorly as a diagnostic technique in the parotids, with levels of false-negative/positive and non-diagnostic rates that are increasingly thought to be unacceptable.
Frozen section has the potential for improving diagnostic yield, but has drawbacks. Parotid tumours are a diverse group, often with complex histological appearances, and making a definitive diagnosis can be challenging for the pathologist in the frozen section operative scenario. More importantly however, the absence of a definitive and accurate diagnosis preoperatively does not allow appropriate operative planning and informed patient consent.
The well-documented problems with FNAC have led to the development of ultrasound-guided core biopsy (USCB) in parotid diagnosis. This technique was not mentioned by the authors, but USCB has become increasingly well recognized and documented. In USCB, diagnostic ultrasound is combined with guiding a small-bore needle (18 or 20 G), which obtains a core of tissue when deployed with an automated biopsy-firing device. The presence of a core of tissue is key, as this can be sent for immunohistochemical analysis, for typing and grading of tumours, and for improved diagnosis of lymphoid hyperplasia (low-grade lymphoma differentiation from reactive nodal hyperplasia). This outpatient procedure is quickly performed under local anaesthesia, and is well tolerated with no significant complications reported. Tumour seeding is not reported to date using these smaller needle gauges. A meta-analysis of 12 USCB series to date reports overall sensitivity of 96%, specificity of 100%, and very low non-diagnostic rates.
It is our view that USCB should be considered as the primary diagnostic tool of choice for parotid swellings. In institutions where FNAC is undertaken and where audited FNAC results show comparable performance, we would advocate USCB as the technique to be undertaken in cases of equivocal or non-diagnostic FNAC. USCB is relatively inexpensive, safe, and highly accurate, allowing a definitive histological diagnosis to be obtained in most patients preoperatively, facilitating timely and appropriate management decisions.