Introduction

Open biopsies are contraindicated because of the risk of tumor cell seeding, which increases the risk of recurrence of both malignant neoplasms and pleomorphic adenomas. Facial nerve injury, wound infection, salivary fistula, or sialocele are reported after open biopsies; in addition, a curative parotid surgery can be complicated by a previous open biopsy.

New surgical procedures for benign tumors such as extracapsular dissection, partial superficial parotidectomy, or deep lobe parotidectomy with preservation of the superficial lobe have been introduced. To avoid an inadequate operation, it is important to know if the lesion is malignant. If malignant, the tumor type and grade are important, as selected low-grade carcinomas may not require total parotidectomy. Currently, the question is, which is more appropriate: fine needle aspiration cytology (FNAC) or core needle biopsy (CNB)? In some centers, frozen section (FS) is standard practice for parotid neoplasms. It is noted that relevant current knowledge is based mainly on retrospective studies.

Fine Needle Aspiration Cytology

FNAC is easy to perform and can be done in an outpatient setting with a 22–25-gauge (G) needle. FNAC allows only limited histo-immunohistochemical analysis of the obtained material, which is composed of variously clustered cells ( Fig. 4.1 ). Numerous studies on the utility and accuracy of FNAC have been published. Due to the different types of reporting, it is difficult to compare the results.

FNAC with foamy macrophages and large cell clusters of tumor cells (within lots of erythrocytes), suspicious of a malignant salivary gland carcinoma (×4).

In 2016, Liu et al. published a meta-analysis including 70 studies with 6784 FNACs. They reported 518 nondiagnostic and 385 indeterminate findings (13.3%). For the diagnostics of malignancy versus benignancy, 63 studies with 5647 FNACs were analyzed. The sensitivity and specificity were 78% and 98%, respectively. Also in 2016, Feinstein et al. analyzed 272 FNACs of parotid gland and 71 of submandibular gland neoplasms. There were 22 nondiagnostic and 39 indeterminate specimens (17.8%). The sensitivity and specificity in the detection of malignant neoplasms of the parotid gland were 75% and 95% and submandibular gland 91% and 94%, respectively. Interestingly, the sensitivity for submandibular gland neoplasms is higher than for parotid gland neoplasms. An analysis, published in 2018, included 477 parotid FNACs and reported a sensitivity and specificity for detecting malignancy of 82% and 90%, respectively. In 26 (5.5%) cases, the FNAC was nondiagnostic. There were 26 (5.5%) false-negative and 29 (6.4%) false-positive findings. The high rate of false-positives is in contrast to most studies reporting higher rates of false-negative than false-positive findings. Few studies analyzed tumor typing: Zbären et al. and Song et al. reported a low accuracy of 35% (24/68 malignant neoplasms) and 18% (10/55 malignant neoplasms), respectively. Accordingly, FNAC may be inappropriate to guide the extent of surgery for malignant neoplasms of the parotid gland.

Major complications such as tumor cell seeding or facial nerve paresis are extremely rare. Shah and Ethunandan analyzed 575 studies including a total of 41,468 FNACs of head and neck masses. Only five cases of seeding were documented, three after FNAC of the parotid gland. Thus, the risk of seeding after FNACS of the head and neck is 0.00012%. The risk of cell seeding seems to be greater in other organs such as the thyroid gland (0.14%) and liver (0.13%). There are no reported cases of facial nerve paresis after FNAC of the parotid.

Core Needle Biopsy

CNB aims at obtaining an adequate sample of tissue with preserved histological architecture ( Fig. 4.2 ). This enables the pathologist to apply a wider range of histochemical stains and immunohistochemical techniques, which may assist in tumor typing and grading. Even extracapsular tumor growth has been occasionally detected in CNB specimens. The CNB is performed under ultrasound guidance after local anesthesia with a 17–20-G needle, depending on the tumor size, location, and the suspected disease process (e.g., lymphoma).

Core needle biopsy-specimen with preserved histological architecture including cyst formation, oncocytic epithelium, and inflammatory cell infiltrate: classical histology of a Warthin tumor.

Kim and Kim in 2018 reported an update of two previous meta-analyses and a systematic review, which included 10 articles published between 2005 and 2016, encompassing 1315 CNBs. The rate of nondiagnostic specimens was 3.6% (46 out of 1268). There were 18 (1.3%) false-positive and 26 (2%) false-negative findings. The pooled sensitivity and specificity in detecting malignant neoplasms were 94% and 98%, respectively. In the two previous meta-analyses of CNB, the accuracy of specific histologic diagnosis was reported to be 96% and 95%; results with respect to tumor grading are lacking.

With the use of CNB, major complications are rarely reported but further data is desirable. In the meta-analysis by Kim and Kim, which, as stated above, included 1315 CNBs, seven (0.5%) hematomas occurred and neither cell seeding nor permanent facial nerve paresis were reported; in one case, a temporary facial nerve weakness was described. In 2016, Shah and Ethunandan analyzed 35 articles including 1803 CNBs of head and neck masses; only two cases of seeding were reported: one in the parotid gland and one in a lymph node. In 2016, Novoa et al. investigated 103 excised needle tracks after CNB of salivary gland lesions, most located in the parotid gland. The examination revealed no tumor displacement in 65 cases, and in 38 cases, the needle track was not identified. The risk of tumor cell seeding after CNB seems to be related to the needle diameter, the tumor type, and the anatomic site of puncture. While needle track recurrences after CNB of breast cancer, thyroid cancer, etc. are described in the literature, no needle track recurrences after CNB of parotid neoplasms have been reported. Authors who are reluctant to endorse regular use of CNB argue that the number of analyzed CNBs of parotid gland neoplasms may be too small and the follow-up too short for detecting needle track recurrences. Also, the risk of injuries of facial nerve branches may potentially be increased in CNBs of neoplasms located in the periphery of the parotid gland, where nerve branches are quite superficial and in some cases lateral to the neoplasm. However, such adverse outcomes have not been reported.

Comparison Between Fine Needle Aspiration Cytology and Core Needle Biopsy

CNB is superior to FNAC in the preoperative diagnosis of parotid neoplasms. CNB has a higher sensitivity in diagnosing malignant tumors, and allows tumor typing and grading in many cases. The specificity of both procedures for discriminating benign from malignant lesions is quite similar. The rate of indeterminate and nondiagnostic specimens is lower with CNB than with FNAC. CNB requires a local anesthesia and is therefore more time-consuming and more expensive than FNAC. The rate of major complications such as tumor cell seeding or facial nerve paresis is low for both procedures. Several authors who performed both FNAC and CNB compared their own experience in retrospective studies and made the same observations. Novoa et al. analyzed in 2016 in a prospective study, comparing FNAC and CNB, 103 patients with salivary gland lesions; they received ultrasound-guided FNAC and CNB. A cytopathologist was present during the FNAC procedure. The sensitivity and specificity in detecting malignant neoplasms for FNAC and CNB were 64 and 94% versus 95 and 100%. The results of CNB were clearly superior to that of FNAC, despite ultrasound-guidance and presence of a cytologist during the FNAC procedure. Others have, however, reported the accuracy of FNAC can be increased by an on-site microscopic evaluation of aspirates performed by a cytologist with ultrasound-guidance. Although CNB is superior to FNAC in the preoperative evaluation of parotid neoplasms, some workers suggest considering CNB when FNAC is equivocal or nondiagnostic.