Malignant Gastrointestinal Stromal Tumor : Distribution, Imaging Features

1. MalignantGastrointestinalStromalTumor: Distribution, Imaging Features PAN ARAB 2012 H. ZAGHOUANI BEN ALAYA, W. BEN AFIA, Z. ACHOUR, M. BARHOUMI, S. MAJDOUB, H. AMARA, D. BAKIR, CH. KRAIEM Imaging department, Farhat Hached Hospital, Sousse, TunisiaMedical GI43

2. I/PURPOSE:

3. To investigate and describe the anatomic distribution, imaging features, and pattern of metastatic spread of gastrointestinal stromal tumors (GISTs).

4. II/INTRODUCTION:

5. GISTs (Gastrointestinal tumors) are a subset of mesenchymal tumors and represent the most common mesenchymal neoplasms of GI (Gastrointestinal) tract.  • Gastrointestinal stromal tumors are KIT-expressing and KIT (tyrosine kinase receptor - CD117)-signaling driven mesenchymal tumors. • TDM is currently the reference imaging examination in the diagnosis, staging and monitoring post therapeutic

6. III/ MATERIALS AND METHODS:

7. The medical records of all patients at our institution with a histological diagnosis of GIST were reviewed, and scans of the primary tumor were available in 25 patients.

8. IV/ RESULTS:

9. 25 patients with malignant GISTs were identified (15 men and 10 women; mean age, 55 years). • The primary tumor locations in descending order of frequency: the small bowel (n = 9), stomach (n = 7), colon (n = 3), rectum (n = 2), other (n = 1), and not specified (n = 3). • Mean primary tumor size was 13 cm ± 6.

10. V/ DISCUSSION:

11. In the present study, the mean age at presentation was over 50 years, in line with that in other series, male predominance is a feature in most previous studies. • The stomach and small bowel consistently account for the vast majority of cases of GIST, usually with a division that favors the stomach. • Multiplicity of primary tumors is rare. The small bowel rather than the stomach was the most common primary site in our series. A possible explanation for this finding could be the misclassification of a number of mesenteric and omental tumors as being of small-bowel origin.

12. Tumors of small-bowel origin tend to have more aggressive behavior and thus a worse prognosis than that of tumors originating in other gastrointestinal sites. In addition to anatomic site, there are a number of other prognosticators. • A poor prognosis is also conferred by: • Advanced patient age. • Large tumor size (>5 cm). • Irresectability; • Metastases at presentation. • Tumor necrosis. • A high mitotic index .

13. The development of local recurrence and metastases at follow-up is a feature of this disease. The distribution of metastases is predictable, with the liver and peritoneum dominating. The liver is the most common metastatic site. Metastases to bone and the lung have been previously described, but they are distinctly uncommon

14. Imaging including ultrasound, CT,MRI and recently PET scan:  Define the diagnosis Guiding possible percutaneous biopsies in cases of advanced or metastatic lesion.  Monitor and early detection of a therapeutic escape

15. Ultrasound:   review of unscramblingduring perception of pain or an abdominal mass. No specificelements for diagnosis. ultrasoundcan shows: a hypoechoicheterogeneous mass intraperitoneal, sometimescontainingcystic areas The livermetastases or peritonealcarcinomatosis

16. CT:  Review of reference. Technical conditions:A markup tract with water or diluted water-soluble contrast can distend the stomach and a better analysis of gastric tumorSpiral acquisitions before and after injection of PCEntero-CT  is indicated in cases of suspected small bowel injuryThe post-processing techniques (RMP MIP) are useful in the analysis of lesions

17. Positive diagnosis: tissue density peripheral enhancement after injection of iodine: 90% homogeneous enhancement: rare (-) central hypodense areas may correspond to necrosis, hemorrhage or cystic formations calcifications rare: 3%

18. The diagnosis of malignant GIST can be suggested on CT scans with the presence of a large well-circumscribed tumor arising from the stomach or small bowel that is usually predominantly extraluminal and has a heterogeneously enhancing soft-tissue rim surrounding a necrotic center. Metastases, if present, will be to the liver or peritoneum.

19. MRI: MRI is reserved for the local pre surgical assessment of pelvic lesions. These include analysis of the relationship between the lesion and the digestive tunics. 

20. large tissue mass  growing at the expense of the gastric wall with central ulceration.

21. Abdominal ultrasound: Pelvic mass well circumscribed, hypoechoic, vascular Doppler.  Metastatic lesions in segments IV and VIII of the liver.

22. Abdominal CT scan:large heterogeneous soft tissue mass, with invasion of the mesenteric small bowelwall adjacent. Liver metastases: three rounded hypodense lesions with peripheral contrast uptake discreet. The most voluminous in segment IV.

23. Abdominal CT scan: large tissue mass, heterogeneous, retro-bladder, displacing the rectum to the right with invasion of its side wall. It is in intimate contact with the sacral vertebrae

24. VI/Conclusion

25. Malignant GISTs are typically large, well-circumscribed, heterogeneous, centrally necrotic tumors that arise in the wall of the small bowel or stomach. They rarely obstruct viscera, despite their large size and propensity to metastasize to the liver and peritoneum.