الفهرس 
COLORECTAL ANATOMYOnly 14 pages are availabe for public view
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Abstract
C
olorectal cancer is the third leading cause of cancer worldwide; it accounts for a large number of tumor related deaths.
Optical colonoscopy represents the reference standard in terms of cancer detection and tissue sampling. However optical colonoscopy only offers an endo-luminal view. Complete ”conventional” staging concepts require additional imaging procedures to assess potential metastatic spread to lymph nodes and solid organs Of these conventional imaging procedures, contrast enhanced computed tomography (CT) is the most common for both the abdomen and pelvis.
CT provides only morphological data for the evaluation of tumor stage, , which may help in determination of lesion size, potential infiltration of adjacent organs or involvement of loco-regional lymph nodes However, A limitation of CT and other radiological imaging procedures pertains to their lack of functional data, inability to determine if a mass is benign or malignant, or to determine if enlarged lymph nodes contain cancer, unable to detect small tumor foci in lymph nodes or elsewhere, inability to determine whether a residual–recurrent abnormality present after treatment represents scar or tumor and extreme difficulty in separating benign postoperative or post radiation changes from viable tumor.
On the other hand, Positron Emission Tomography (PET); which is a tomographic scintigraphic technique in which a computer generated image of local radioactive tracer (FDG) distribution in tissues is produced through the detection of annihilation photons that are emitted when radionuclides introduced into the body decay and release positrons by surrounding the patient’s body (or a part of the patient’s body) with multiple rings of specialized detector crystals, provides functional information but its main drawback of showing few anatomic landmarks impedes precise localization of sites of pathologic 18F-FDG uptake. In addition, there are some issues regarding specificity, because 18F-FDG is taken up not only by many malignant tumors but also by sites of active inflammation and physiologically by some organ.
Thus fusion of functional with morphological data may be of benefit for tumor staging. As a consequence, combined ’’POSITRON EMISSION TOMOGRAPHY – COMPUTED TOMOGRAPHY’’ [PET/CT] scanner has been introduced into clinical practice. Its ability to detect and characterize malignant lesions with advantages over morphology and function alone has been documented for different tumors including colorectal cancer.
This work discusses the role of PET-CT in colorectal cancer.
The anatomy of the colorectum was shown and the pathology of colorectal tumors was discussed.There are 3 pathological types of colorectal tumors: Benign, precancerous conditions and malignant tumors.
Early diagnosis and precise staging of the colorectal cancer is one of the most important factors in determining prognosis and treatment options.
Integrated PET/CT produce directly functional PET and anatomical CT data in one session, after certain patient preparation, without moving the patient and with minimal delay between the reconstruction and fusion of the two image data sets.
Advantages of PET/CT over other imaging modalities include: differentiating benign from malignant lesions, selecting the region of a tumor most likely to yield diagnostic information for biopsy Guiding treatment and radiation therapy planning with Monitoring the effect of therapy, detecting tumor recurrence especially in the absence of elevated levels of tumor markers, ability to distinguish viable metabolically active tissue from scars, helps identify cancer that has spread even if other tests (CT, MRI, ultrasound) cannot find it and better restaging in patients with suspected recurrent and metastatic disease.
The main drawbacks of PET/CT in management of colorectal cancer include: Radiation exposure, cost, attenuation correction and motion artifacts, False positive results in case of physiological uptake, inflammation (e.g., diverticulitis, colitis), polyps and stoma site/postoperative changes and False negative results in case of small volume disease < 1cm and mucinous secreting tumors.
In practice, PET-CT is rarely used for primary diagnosis of CRC. Yet, PET-CT has been reported to have a 92% accuracy in CRC staging specially stages III and IV, 100% sensitivity and 97% specificity 97.3% accuracy in detection of local and distant recurrence. It has a 94% sensitivity and 75% specificity in detecting hepatic metastasis. Altering management plan has been reported in 25% of patients with colorectal cancer after examination with PET-CT.
To conclude, PET-CT imaging technique plays an important role in patients with colorectal cancer specially in staging, restaging and detection of recurrence, treatment planning and selection of patients with hepatic metastasis for hepatectomy.