PAP/NGC Programs Review
Michael Henry, MD
Aspiration biopsies of the salivary glands are common specimens in most pathology
practices and can present with quite difficult diagnostic challenges. The list
of malignant and benign neoplastic lesions as well as other processes that can
present as masses is extensive with considerable cytologic overlap. Several
large series have documented the utility of FNA of the salivary gland with a
reported overall accuracy ranging from 87 percent to 100 percent in distinguishing
benign from malignant. However, most of these series were generated at large
academic centers and may not represent everyday practice in the community.
With this in mind, Jonathan Hughes, MD, PhD, and colleagues used data derived
from the CAP Interlaboratory Comparison Program in Nongynecologic Cytology to
identify common diagnostic errors in salivary gland aspirates (Arch
Pathol Lab Med. 2005;129:26–31). This study is unique in that
the nongyn program assesses the diagnostic accuracy of a diverse group of practicing
pathologists including academic centers, commercial laboratories, and large
and small private practices.
The study had two parts, looking first at overall accuracy in diagnosing salivary
lesions by FNA and then identifying individual cases with a high level of discordance
between the reference diagnosis and the participant responses. There were 4,642
responses from cases with a reference diagnosis of benign and 1,607 responses
from cases with a reference diagnosis of malignant, for a total of 6,249 responses
evaluated for the study. The specificity in making a benign diagnosis was 91
percent with a false-positive rate of eight percent. In these benign cases there
was a 76 percent accuracy rate in making a correct specific diagnosis. The sensitivity
in making a malignant diagnosis was 68 percent with a false-negative rate of
32 percent. The highest false-negative rates were seen in cases of lymphoma
(57 percent), acinic cell carcinoma (49 percent), low-grade mucoepidermoid carcinoma
(43 percent), and adenoid cystic carcinoma (33 percent). The accuracy in making
a correct specific malignant diagnosis was 48 percent.
Selected review of the most discordant cases provided insight into sources
of possible misinterpretation. The failure to recognize diagnostically helpful
components such as stromal elements in adenoid cystic carcinoma, oncocytic cells
in Warthin’s tumor, the monomorphic nature of lymphocytes in lymphoma,
and the architectural disarray of acinar structures in acinic cell carcinoma
seemed to contribute to misinterpretation issues. The importance of using a
Romanowsky type stain, such as Diff-Quik, along with a Papanicolaou stain was
emphasized as well as the usefulness of ancillary studies such as flow cytometry
in atypical lymphoid lesions.
The authors concluded that awareness of these potential pitfalls and the application
of classic cytologic criteria may help improve the performance of salivary gland
FNA in clinical practice.
Dr. Henry, a member of the CAP Cytopathology Committee, is staff pathologist
at Cleveland Clinic Florida, Naples.