The TNM classification system for jejunoileal neuroendocrine tumors uses three key classifications to determine the stage of the tumor: tumor classification, lymph node classification, and distant metastasis. Users provide their selections among specific predefined options for each category. Based on these selections, the system computes the tumor stage using established criteria.

For tumor classification, the options include:

- Tx: Primary tumor cannot be assessed
- T0: No evidence of primary tumor
- T1: Tumor less than or equal to 1 cm and invades lamina propria or submucosa
- T2: Tumor greater than 1 cm or invades muscularis propria
- T3: Tumor invades through muscularis propria into subserosal tissue without penetration of the overlying serosa
- T4: Tumor invades visceral peritoneum or other organs or adjacent structures

Lymph node assessment options are:

- Nx: Regional lymph nodes cannot be assessed
- N0: No regional lymph node metastasis
- N1: Regional lymph node metastases in fewer than 12 nodes
- N2: Large mesenteric masses (more than 2 cm) and/or extensive nodal deposits (12 or more), especially encasing superior mesenteric vessels

Finally, distant metastasis options include:

- M0: No distant metastasis
- M1a: Metastasis confined to the liver
- M1b: Metastases in one or more extrahepatic sites, such as the lung, ovary, nonregional lymph node, peritoneum, and bone
- M1c: Metastases in both hepatic and extrahepatic sites

The system then applies a logic to map combinations of these selections to specific cancer stages:

- Stage I is identified when the selections are T1, N0, and M0.
- Stage II is determined by T2 or T3, combined with N0 and M0.
- Stage III encapsulates conditions where selections meet one of these patterns:
  - Tumor classifications T1, T2, or T3 with lymph node classifications N1 or N2, and M0.
  - A tumor classified as T4 with any lymph node classification and M0.
- Stage IV is assigned when any tumor classification (T1 through T4) with any lymph node classification and distant metastasis (M1a, M1b, or M1c) are selected.

Using these combinations, the TNM classification system effectively interprets and provides a stage designation for jejunoileal neuroendocrine tumors, guiding clinical decision-making by carefully considering tumor size, location, lymph node involvement, and metastasis status.

The TNM classification for jejunoileal neuroendocrine tumors is a clinical staging system developed by the American Joint Committee on Cancer (AJCC). It is designed to stratify patients with jejunoileal neuroendocrine tumors based on the extent of the disease, which aids in guiding treatment decisions and predicting prognosis. 

The primary components of this classification system include the size and extent of the primary tumor (T), the presence and extent of regional lymph node involvement (N), and the presence of distant metastasis (M). Each of these components is assigned a numerical value, with higher values indicating more advanced disease. 

The T category is determined by the size of the primary tumor and its extent of invasion into the surrounding tissues. The N category is determined by the number and location of regional lymph nodes involved. The M category is determined by the presence or absence of distant metastasis. 

The final TNM stage is determined by combining the T, N, and M categories. This stage provides a comprehensive picture of the patient's disease status and is used to guide treatment decisions and predict prognosis. 

Exclusion criteria for this classification system include patients with neuroendocrine tumors of other gastrointestinal sites, as the TNM classification for jejunoileal neuroendocrine tumors is specific to tumors originating in the jejunum and ileum.