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Case Reports
. 2026 Mar 4;17(4):170-175.
doi: 10.14740/jmc5203. eCollection 2026 Apr.

Extranodal Marginal Zone B-cell Lymphoma Presenting as a Painless Buccal Mass in the Masticator Space

Li Lin  1 , Jiun-Sheng Lin  1   2
Affiliations
Case Reports

Extranodal Marginal Zone B-cell Lymphoma Presenting as a Painless Buccal Mass in the Masticator Space

Li Lin et al. J Med Cases. .

Abstract

Extranodal marginal zone B-cell lymphoma (EMZL, mucosa-associated lymphoid tissue type) is an indolent non-Hodgkin lymphoma that only rarely arises in deep facial spaces. Primary masticator-space involvement is particularly uncommon and can mimic benign buccal soft-tissue lesions. We report a 67-year-old woman with a 4-year history of a painless, slowly enlarging left cheek mass. Examination showed a soft, mobile 3-cm buccal swelling with normal overlying skin and no intraoral lesion. Contrast-enhanced computed tomography demonstrated an infiltrative soft-tissue mass measuring 3.1 × 1.5 × 3.5 cm, centered in the left masticator space, with effacement of fat planes between the masseter, pterygoid, and temporalis muscles. Intraoral incisional biopsy revealed a dense infiltrate of small-to-medium CD20-positive, Bcl-2-positive B cells, with a CD5, CD10, CD23, Bcl-6-negative immunophenotype and follicular colonization on CD21 staining, consistent with EMZL. A multidisciplinary tumor board recommended involved-site radiotherapy to the masticator space combined with rituximab-based immunotherapy. This case represents a rare example of primary EMZL arising in the masticator space, which highlights the need to include lymphoma in the differential diagnosis of persistent head and neck masses, to obtain tissue diagnosis for infiltrative head and neck lesions and to coordinate organ-preserving treatment through multidisciplinary care.

Keywords: Buccal mass; Head and neck lymphoma; MALT lymphoma; Marginal zone lymphoma; Masticator space; Radiotherapy; Rituximab.

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Conflict of interest statement

Li Lin and Jiun-Sheng Lin declare no conflict of interest relevant to this work.

Figures

Figure 1
Figure 1
Physical examination revealed a soft, mobile, subcutaneous mass (about 3 cm) in the left buccal region (arrows).
Figure 2
Figure 2
Contrast-enhanced computed tomography revealed an infiltrative soft-tissue mass measuring 3.1 × 1.5 × 3.5 cm, centered in the masticator space with effacement of fat planes between the masseter, pterygoid, and temporalis muscles.
Figure 3
Figure 3
An intraoral incisional biopsy under general anesthesia with obtained specimen (arrows). The intraoral approach allowed direct access to the bucco-masseteric space while avoiding external scarring.
Figure 4
Figure 4
H&E stain (× 40) demonstrating a diffuse, vaguely nodular infiltrate, expanding the soft tissue and disrupting normal architectural boundaries. Note the presence of mild plasmacytic differentiation (arrows). H&E: hematoxylin and eosin.
Figure 5
Figure 5
(a) Representative immunohistochemistry demonstrating diffuse CD20 positivity in the neoplastic B cells within the masticator-space lesion (× 200). (b) Bcl-2 staining highlights strong cytoplasmic expression in the small B cells, supporting a diagnosis of EMZL rather than reactive hyperplasia (× 200). EMZL: extranodal marginal zone B-cell lymphoma.
Figure 6
Figure 6
(a) CD3 negativity in the tumor cell population confirms that the predominant infiltrate is of B-cell rather than T-cell lineage (× 200). (b) Lack of CD5 expression helps to exclude mantle cell lymphoma and most chronic lymphocytic leukemia/small lymphocytic lymphoma (× 200). (c) The neoplastic lymphoid infiltrate is negative for CD10, supporting a marginal zone origin and helping exclude follicular lymphoma (× 200). (d) The neoplastic lymphoid population is negative for CD23 expression, helping distinguish this case from small lymphocytic lymphoma (× 200). (e) CD43 negativity in the neoplastic B cells is consistent with an EMZL phenotype and argues against other small B-cell lymphomas (× 200). (f) Bcl-6 negativity in the neoplastic lymphoid cells (× 200). This lack of Bcl-6 expression supports a post-germinal center origin and helps exclude follicular lymphoma. EMZL: extranodal marginal zone B-cell lymphoma.
Figure 7
Figure 7
CD21 outlining disrupted follicular dendritic cell meshworks consistent with follicular colonization (arrows).
See this image and copyright information in PMC

References

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