Intraoperative Imprint Cytology of SMARCB1-Mutant Desmoplastic Myxoid Tumor of the Pineal Region: A Case Report with Cytologic Differential Diagnosis and Literature Review.

OBJECTIVE: Desmoplastic myxoid tumor of the pineal region (DMTPR), SMARCB1-mutant, is a recently recognized and rare pineal region tumor with distinctive clinicopathologic features that contrast sharply with those of atypical teratoid/rhabdoid tumor, a well-known SMARCB1-deficient neoplasm. Although DMTPR generally exhibits low- to intermediate-grade histologic features and relatively indolent clinical behavior, its rarity and morphologic overlap with other pineal region neoplasms may pose significant diagnostic challenges, particularly during intraoperative consultation when tissue is limited.

CASE REPORT: We report a case of DMTPR in a 38-year-old woman, with particular emphasis on its intraoperative touch imprint cytologic findings and their correlation with histologic features. The imprint preparations were composed of bland, relatively monomorphic oval-to-spindled tumor cells with delicate fibrillary processes embedded in a myxoid background. Small fibrillary acellular zones with variably collagenous areas were also identified, closely mirroring the tumor's characteristic myxoid to myxofibrillary histology with irregular anastomosing collagenous structures.

CONCLUSION: This case expands the limited literature describing the cytologic features of DMTPR and highlights the value of touch imprint cytology as a useful adjunct to frozen-section evaluation. Recognition of its distinctive cytomorphologic features is important to avoid misclassification as other pineal region tumors during intraoperative assessment and to guide appropriate patient management.