Endoscopic Ultrasound-Guided Fine-Needle Aspiration Cytology Diagnosis of Solid-Pseudopapillary Tumor of the Pancreas: A Rare Neoplasm of Elusive Origin but Characteristic Cytomorphologic Features

Clinical histories, endoscopic ultrasound (EUS)-guided fine-needle aspiration (FNA) material, and immunohistochemical stains performed on cell block samples of 6 solid-pseudopapillary tumors of the pancreas (SPTPs) were reviewed in the cases of 5 females (13-58 years) and 1 man (57 years); all had abdominal pain. Preliminary cytologic diagnoses at endoscopy included 1 SPTP, 2 low-grade neoplasms, and 3 pancreatic endocrine tumors. Variable numbers of branching fragments with central capillaries and myxoid stroma were seen in the smears of 5 of 6 cases but were more apparent in the cell block material of all cases. The cells had bland nuclear features and rare grooves. Extensive necrosis was noted in 1 case and rare mitotic figures in 1. SPTPs showed strong cellular immunoreactivity for vimentin and focal weak keratin reactivity. Neuron-specific enolase, α₁-antitrypsin, and α ₁-antichymotrypsin stains performed in 2 cases were strongly positive. Subsequent surgical resection confirmed all diagnoses. EUS-guided FNA diagnosis of SPTP is accurate. The characteristic branching papillae with myxoid stroma are best seen in cell block slides. Clinical setting, cytomorphologic features, and immunostains of the cell block help distinguish SPTP from pancreatic endocrine tumors, acinar cell carcinoma, and papillary mucinous carcinoma.