Histopathology

At low magnification, the pattern of the cysts is similar to a sponge. The cysts contain proteinaceous fluid and are lined by a single layer of cuboidal or flattened epithelial cells. Their cytoplasm is clear and only rarely eosinophilic and granular. The nuclei are centrally located, round to oval in shape, uniform, and have an inconspicuous nucleolus. Due to the presence of abundant intracytoplasmic glycogen, the periodic acid-Schiff (PAS) stain without diastase digestion is positive, whereas PAS-diastase and Alcian blue stains are negative {160}. Mitoses are practically absent and there is no cytological atypia. Occasionally, the neoplastic cells form intracystic papillary projections, usually without a fibrovascu-lar stalk. The central fibrous stellate core is formed of hyalinized tissue with a few clusters of tiny cysts.

Immunohistochemistry

The epithelial nature of these neoplasms is reflected in their immunoreactivity for epithelial membrane antigen and cytok-eratins 7, 8, 18, and 19. In addition, the neoplastic cells may focally express CA19-9 and B72.3 {815, 1752}. They are uniformly negative for carcinoembryonic

Fig. 10.11 Serous oligocystic adenoma. This CT scan shows a macrocystic neoplasm in the head of the pancreas.

antigen (CEA), trypsin, chromogranin A, synaptophysin, S-100 protein, desmin, vimentin, factor VIII-related antigen and actin {49, 119, 445, 689, 815, 1752, 1781, 2151}.

Ultrastructure

Electron microscopy shows a single row of uniform epithelial cells lining the cysts and resting on a basal lamina {49, 160, 915}. The apical surfaces have poorly developed or no microvilli. The cytoplasm contains numerous glycogen granules but only a few mitochondria, short profiles of endoplasmic reticulum, lipid droplets, and multivesicular bodies. Golgi complexes are rarely identified. Zymogen granules and neurosecretory granules are absent.

Genetics

Loss of heterozygosity at the von Hippel-Lindau (VHL) gene locus, mapped to chromosome 3p25, was found in 2/2 serous microcystic adenomas associated with VHL disease and in 7/10 sporadic cases {2026}. In contrast to ductal adenocarcinomas, serous microcystic adenomas have wild-type KRAS and lack immunoreactivity for TP53{815}.

Prognosis

The prognosis of patients with this neoplasm is excellent, since there is only a minimal risk of malignant transformation {1159}.

Serous oligocystic adenoma Definition

A benign neoplasm composed of few, relatively large cysts, lined by uniform glycogen-rich cuboidal epithelial cells.

Synonyms

This tumour category includes macro-cystic serous cystadenoma {257, 1062}, serous oligocystic and ill-demarcated adenoma {445}, and some cystade-nomas observed in children {2057}. Whether these neoplasms form a homogeneous group remains to be established.

Epidemiology

Serous oligocystic adenomas are much less common than serous microcystic adenomas {445, 1062}. There is no sex predilection. Adults are usually 60 years and over (age range, 30-69 years; mean, 65 years); the tumour has been described in two male and two female infants, aged between 2 and 16 months {1781}.

Fig. 10.13 Serous cystadenoma. A cystic neoplasm replaces the head of the pancreas; a portion of duodenum is on the right.

Aetiology

The aetiology of this neoplasm is not known. In children, it has been suggested that the lesions may be of malforma-tive origin and not true neoplasms since in two cases there was a cytomegalo-virus infection in the adjacent pancreas {52, 273}.

Localization

Most serous oligocystic adenomas are located in the head and body of the pancreas {1781}. In the head, they may obstruct the periampullary portion of the common bile duct.

Clinical features

In most cases reported in adult patients, the neoplasms caused symptoms that led to their discovery and removal. The most common symptom was upper abdominal discomfort or pain {1781}. Other symptoms included jaundice and steatorrhoea. In infants, the tumours presented as a palpable abdominal mass {52, 273}.

Macroscopy

These neoplasms typically appear as a cystic mass with a diameter of 4-10 cm (mean, 6 cm) {1781}. On cut surface,

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