Signet-ring cell variant of small lymphocytic lymphoma with a prominent sinusoidal pattern

Pitfalls in Lymph Node Fine Needle Aspiration Cytology

BACKGROUND

Fine needle aspiration cytology (FNAC) is an accurate, minimally invasive, and cost-effective biopsy method for enlarged lymph nodes. While the role of lymph node FNAC in the diagnosis of infectious or reactive conditions and metastatic malignancy is unquestioned, differing views still exist on its role in the diagnosis of lymphoma. Nevertheless, regardless of the practice setting, pitfalls and potential for error exist, and it is incumbent upon the pathologist to be aware of these pitfalls, as this is the first line of defence against errors.

SUMMARY

This discussion will focus on potential interpretational errors, specifically highlighting scenarios leading to false-negative and false-positive diagnosis and errors in tumour classification, with an emphasis on cytomorphology. Potential entities that may fly below the radar of the pathologist - so-called off-radar entities - are also discussed, as a reminder to consider broad differentials in cases with unusual morphologic features. Some reasons for false-negative diagnoses include low-grade lymphomas that mimic a mixed, polymorphous reactive lymphoid population or aspirates with a paucity of lesional cells, through either sampling error or the intrinsic nature of the entity, e.g., nodular lymphocyte predominant Hodgkin lymphoma. Some of the potential causes of false-positive diagnoses that are discussed include viral-associated lymphadenopathy, Kikuchi-Fujimoto lymphadenitis, or benign adnexal lesions mimicking metastatic malignancy. Errors in tumour classification covered include metastatic carcinoma, sarcoma, melanoma, and lymphoma mimicking each other, and Hodgkin lymphoma and its mimics. Finally, less common entities such as follicular dendritic cell sarcoma and others are briefly mentioned, to remind us of conditions that may slip under our diagnostic radar.

KEY MESSAGES

A systematic review of diagnostic pitfalls and traps is elucidated here, with some tips to avoid these traps. The triple approach to the diagnostic workup is emphasised, which includes rigorous clinicopathologic correlation, attention to cytomorphology, and judicious application of ancillary tests.

The broad landscape of follicular lymphoma: Part I

Follicular lymphoma is a neoplasm derived from follicle center B cells, typically both centrocytes and centroblasts, in variable proportions according to the lymphoma grading. The pattern of growth may be entirely follicular, follicular and diffuse, and rarely completely diffuse. It represents the second most common non-Hodgkin lymphoma, after diffuse large B-cell lymphoma and is the most common low-grade mature B-cell lymphoma in western countries. In the majority of cases, follicular lymphoma is a nodal tumor, occurring in adults and frequently associated with the translocation t(14;18)(q32;q21)/IGH-BCL2. However, in recent years the spectrum of follicular lymphoma has expanded and small subsets of follicular lymphoma, which differ from common follicular lymphoma, have been identified and included in the current 2017 WHO classification. The aim of our review is to describe the broad spectrum of follicular lymphoma, pointing out that the identification of distinct clinicopathological variants of follicular lymphoma is relevant for patient outcomes and choice of treatment.

Fine-needle aspiration diagnosis of lymphomas with signet ring cell features: potential pitfalls and solutions

BACKGROUND

Lymphoma with signet ring cell features (LSF) is a rare morphologic variant of non-Hodgkin lymphoma. Although it has been well documented in the surgical pathology literature, to the best of the authors's knowledge, the features of LSF in fine-needle aspiration (FNA) samples have rarely been reported. An accurate cytologic diagnosis of LSF is of important therapeutic significance.

METHODS

The authors retrospectively reviewed 7 FNA cases of LSF for cytologic features, ancillary studies, corresponding histologic findings, and the patients' clinical and radiologic information to illustrate the diagnostic clues and potential pitfalls.

RESULTS

The final diagnoses, based on a multidisciplinary approach, were follicular lymphoma (5 patients), large B-cell lymphoma of follicular center cell origin (1 patient), and low-grade B-cell lymphoma with plasmacytoid features (1 patient). FNAs were obtained from both lymph node and extranodal sites. Common cytologic features included various percentages of signet ring cells in a background of nonvacuolated lymphomatous cells, lymphoglandular bodies, and cytoplasmic rings. The majority of signet ring cells contained a single, large, clear intracytoplasmic vacuole that pushed the nucleus laterally whereas fewer cells contained ≥ 2 vacuoles that indented the nucleus into a scalloped or stellate configuration. These cells resemble, to some degree, other lesions with signet ring cell features. One of the diagnostic clues of LSF was the similarity in nuclear details between signet ring cells and surrounding nonvacuolated lymphoid cells.

CONCLUSIONS

Familiarity with cytologic features, correlation with clinical/radiologic information, and ancillary studies are important for an accurate diagnosis of LSF and for distinguishing it from other lesions with signet ring cell features in FNA samples.

Signet ring lymphoma: a potential diagnostic mishap

Signet ring lymphomas are proliferations of malignant lymphoid cells containing cytoplasmic inclusions or vacuoles that displace the nucleus to the side, imparting a "signet ring" appearance. These signet ring cells, particularly those with cytoplasmic vacuoles, may be mistaken for an adenocarcinoma rather than a lymphoma, if sufficient material is not available to differentiate the case by immunohistochemical stains or flow cytometry. The pathologist must also be aware of this entity so that appropriate studies may be untaken.

Extreme Signet Ring Cell Change in a Large B-Cell Lymphoma of Follicular Origin

We report a large B-cell lymphoma of follicular origin with extreme signet ring cell differentiation. Initially classified as follicular lymphoma on a fine needle core biopsy, the presence of cohesive sheets of extrafollicular signet ring cells triggered an excisional biopsy for further characterization. The excised lymph node revealed focal follicular hyperplasia, follicular lymphoma, and a neoplasm composed of vague nodules and sheets of large atypical cells, all of which virtually exhibited large clear intracytoplasmic vacuoles with peripheral displacement of nuclei. The tumor cells were negative for mucin and lacked immunoreactivity with pancytokeratin, but were strongly immunoreactive with CD20, BCL-2, BCL-6, and CD10 antibodies. Electron microscopy studies revealed electron-lucent vacuoles with no particular internal structure. This case is unique in that extreme signet ring cell differentiation somewhat obscured the true cytological identity of the interfollicular lymphoma and suggested alternative diagnoses.

An unusual uterine tumor with signet ring cell features

In 2004, a 56-year-old woman was diagnosed with Stage IA follicular lymphoma in a cervical lymph node biopsy. The patient experienced total remission after local radiation therapy. In 2009, a control computed tomography scan evidenced a pelvic mass, prompting total hysterectomy. The latter harbored a 4.8-cm intramural uterine tumor corresponding to a mostly diffuse and focally nodular proliferation of medium to large cells, with extensive, periodic acid-Schiff negative, signet ring cell changes, and a pan-keratin negative, CD20+, CD10+, Bcl2+, Bcl6+ immunophenotype. Molecular genetic studies showed the same clonal IGH gene rearrangement in the lymph node and the uterus, establishing the uterine tumor as a relapse of the preceding follicular lymphoma, although no signet ring cells were evidenced at presentation. Uterine localization of lymphomas is rare, and lymphomas with signet ring cell features are uncommon. This exceptional case exemplifies a diagnostically challenging situation and expands the differential diagnosis of uterine neoplasms displaying signet ring cell morphology.

Signet ring cell gastric schwannoma: report of a new distinctive morphological variant

An 89-year-old woman was seen for indigestion, light chest pain, and melanotic stools. Endoscopic examination revealed 2 submucosal gastric masses. A subtotal gastrectomy showed 2 submucosal masses in the stomach: one infiltrating through the muscularis propria into the serosa, the second one, a well-circumscribed submucosal nodule. Histologic examination showed large tumor cells infiltrating diffusely through the muscularis propria into the subserosa. On higher magnification, numerous signet ring cells were present against a myxoid stroma, in addition to large vacuolated epithelioid cells. There was no evidence of invasion, necrosis, nuclear pleomorphism, or mitotic activity. Initial diagnostic considerations based on the histology included signet ring cell carcinoma, malignant melanoma, and a myxoid mesenchymal tumor, including gastrointestinal stromal tumor. A panel of immunohistochemical stains showed diffuse strong positivity for S-100 protein and negative reaction for CD117, bcl-2, cytokeratin AE1/AE3, Melan-A, HMB45, smooth muscle antigen, and other differentiation markers. Electron microscopic examination revealed elongated, complex, and interdigitating cell processes covered by a thin layer of continuous basement membrane material characteristic of peripheral nerve sheath differentiation. The presentation of this tumor was significant in that it was multifocal and infiltrative, mimicking a malignant neoplasm. The extensive myxoid/signet ring cell change represents a heretofore-unreported histologic variant of gastric schwannoma.