Histological Classification of Neoplasms
Pathological anatomy traditionally relies on the WHO histological classification of tumors. According to this classification, all pancreatic neoplasms are divided into several major categories based on their tissue origin:
- Epithelial tumors. This is the most significant group, subdivided into benign variants (adenoma and cystadenoma) and malignant variants. The malignant spectrum includes adenocarcinoma, squamous cell carcinoma, cystadenocarcinoma, acinar cell carcinoma, and undifferentiated carcinoma.
- Pancreatic islet tumors. Formed from the endocrine portion of the organ.
- Non-epithelial tumors. Develop from stromal elements.
- Mixed tumors. Combine elements of different tissues.
- Unclassified tumors. Neoplasms that cannot be assigned to a specific group.
- Hematopoietic and lymphoid tumors.
- Metastatic tumors. Secondary deposits originating from other organs.
Morphology of Benign Tumors: Cystadenoma
Among benign epithelial neoplasms, cystadenoma deserves special attention. This is a relatively rare pathology with a very specific macroscopic and microscopic picture.
- Macroscopy: The tumor often reaches large sizes. On cross-section, it has a distinct multilocular structure, appearing as a conglomerate of cystic cavities.
- Histology: The cavities of the cystadenoma are lined internally by epithelial cells. A crucial differential diagnostic feature is that this epithelium actively accumulates glycogen while not producing any mucus.
- Diagnostic imaging: During angiography, the appearance changes depending on the study phase. In the arterial phase, the lesion appears as a well-vascularized area with a rich vascular network. In the parenchymal phase, the tumor shadow becomes heterogeneous due to the presence of multiple fluid-filled cysts that do not take up contrast.
Pancreatic Carcinoma: Growth Patterns and Histogenesis
Malignant epithelial tumors can affect virtually any part of the organ, but statistically they are most frequently localized in the head.
- Carcinoma of the head: Macroscopically, the tumor presents as a very dense, gray-white nodule. The margins of this nodule are ill-defined, indicating an invasive growth pattern and infiltration into surrounding healthy tissues.
- Carcinoma of the body and tail: Neoplasms in this location often reach considerable sizes. This is because they grow completely asymptomatic for a long time. Unlike tumors of the head, they do not cause dysfunction of surrounding organs or obstruct vital ducts for a prolonged period.
From the perspective of histogenesis (tissue origin), malignant tumors of the exocrine pancreas are divided into two main types. If the tumor develops from the epithelium of the excretory ducts, adenocarcinoma forms. If the source of malignant growth is the acini of the exocrine parenchyma, acinar (alveolar) cell carcinoma arises.
Pathogenesis of Complications, Metastasis, and Outcomes
Localization of carcinoma in the pancreatic head triggers a severe cascade of complications. The growing dense nodule first causes compression and then direct invasion into the walls of the pancreatic ducts and the common bile duct.
Consequences of this growth:
- Impairment of normal pancreatic function due to ductal obstruction, leading to secondary pancreatitis.
- Impairment of liver function. Obstruction of the biliary tract causes cholangitis and extrahepatic (obstructive) jaundice.
Routes of metastasis:
- Lymphatic spread: The pathway for early metastases. Tumor cells settle in regional lymph nodes located directly around the head of the pancreas.
- Hematogenous spread: Characteristic of late stages of the disease. Via blood vessels, late metastases are carried to the liver and other distant organs.
Death from pancreatic cancer most frequently results from severe body wasting (cachexia), multiple life-incompatible metastases, or superimposed infectious complications such as severe pneumonia.