Imaging in gastrointestinal stromal tumours: current status and future directions

Small Bowel Gastrointestinal Stromal Tumors: The Value of CT Enterography in Assessing Pathological Aggressiveness

OBJECTIVE

This study aimed to characterize the computed tomography (CT) enterography features of the small bowel gastrointestinal stromal tumors (GIST) and to determine the association with pathological aggressiveness.

METHODS

Computed tomography enterography images of 30 patients with the histologically confirmed small bowel GIST were retrospectively enrolled. Tumor size, location, border, growth pattern, enhancement pattern, necrosis, calcification, ulceration, internal air, nodal metastasis, liver metastasis, peritoneal metastasis, and draining vein were evaluated. Relationships between imaging features and pathological aggressiveness were analyzed using χ2 test or Fisher exact test. Correlations among CT features were analyzed using Spearman correlation analysis.

RESULTS

There were significant differences in tumor size between different risk levels (F = 8.388, P < 0.001). There were statistically significant differences in the 5 imaging manifestations of necrosis, ulcer, tumor boundary, drainage vein, and intratumoral gas (P < 0.05). There was a significant negative correlation between tumor size and enhancement type as well as clear tumor boundary. There was a significant positive correlation between tumor size and necrosis, ulcer, drainage vein, intratumoral gas, liver metastasis, and peritoneal metastasis.

CONCLUSIONS

Some CT enterography imaging features might be useful in the determination of the pathological aggressiveness in the patients with small bowel GIST.

Gastrointestinal stromal tumors: a comprehensive radiological review

Gastrointestinal stromal tumors (GISTs) originating from the interstitial cells of Cajal in the muscularis propria are the most common mesenchymal tumor of the gastrointestinal tract. Multiple modalities, including computed tomography (CT), magnetic resonance imaging (MRI), fluorodeoxyglucose positron emission tomography, ultrasonography, digital subtraction angiography, and endoscopy, have been performed to evaluate GISTs. CT is most frequently used for diagnosis, staging, surveillance, and response monitoring during molecularly targeted therapy in clinical practice. The diagnosis of GISTs is sometimes challenging because of the diverse imaging findings, such as anatomical location (esophagus, stomach, duodenum, small bowel, colorectum, appendix, and peritoneum), growth pattern, and enhancement pattern as well as the presence of necrosis, calcification, ulceration, early venous return, and metastasis. Imaging findings of GISTs treated with antineoplastic agents are quite different from those of other neoplasms (e.g. adenocarcinomas) because only subtle changes in size are seen even in responsive lesions. Furthermore, the recurrence pattern of GISTs is different from that of other neoplasms. This review discusses the advantages and disadvantages of each imaging modality, describes imaging findings obtained before and after treatment, presents a few cases of complicated GISTs, and discusses recent investigations performed using CT and MRI to predict histological risk grade, gene mutations, and patient outcomes.

Assessment of morphological CT imaging features for the prediction of risk stratification, mutations, and prognosis of gastrointestinal stromal tumors

OBJECTIVES

To investigate the correlation between CT imaging features and risk stratification of gastrointestinal stromal tumors (GISTs), prediction of mutation status, and prognosis.

METHODS

This retrospective dual-institution study included patients with pathologically proven GISTs meeting the following criteria: (i) preoperative contrast-enhanced CT performed between 2008 and 2019; (ii) no treatments before imaging; (iii) available pathological analysis. Tumor risk stratification was determined according to the National Institutes of Health (NIH) 2008 criteria. Two readers evaluated the CT features, including enhancement patterns and tumor characteristics in a blinded fashion. The differences in distribution of CT features were assessed using univariate and multivariate analyses. Survival analyses were performed by using the Cox proportional hazard model, Kaplan-Meier method, and log-rank test.

RESULTS

The final population included 88 patients (59 men and 29 women, mean age 60.5 ± 11.1 years) with 45 high-risk and 43 low-to-intermediate-risk GISTs (median size 6.3 cm). At multivariate analysis, lesion size ≥ 5 cm (OR: 10.52, p = 0.009) and enlarged feeding vessels (OR: 12.08, p = 0.040) were independently associated with the high-risk GISTs. Hyperenhancement was significantly more frequent in PDGFRα-mutated/wild-type GISTs compared to GISTs with KIT mutations (59.3% vs 23.0%, p = 0.004). Ill-defined margins were associated with shorter progression-free survival (HR 9.66) at multivariate analysis, while ill-defined margins and hemorrhage remained independently associated with shorter overall survival (HR 44.41 and HR 30.22). Inter-reader agreement ranged from fair to almost perfect (k: 0.32-0.93).

CONCLUSIONS

Morphologic contrast-enhanced CT features are significantly different depending on the risk status or mutations and may help to predict prognosis.

KEY POINTS

• Lesions size ≥ 5 cm (OR: 10.52, p = 0.009) and enlarged feeding vessels (OR: 12.08, p = 0.040) are independent predictors of high-risk GISTs. • PDGFRα-mutated/wild-type GISTs demonstrate more frequently hyperenhancement compared to GISTs with KIT mutations (59.3% vs 23.0%, p = 0.004). • Ill-defined margins (hazard ratio 9.66) were associated with shorter progression-free survival at multivariate analysis, while ill-defined margins (hazard ratio 44.41) and intralesional hemorrhage (hazard ratio 30.22) were independently associated with shorter overall survival.

Role of Multidetector CT Imaging in the Risk Stratification of Gastrointestinal Stromal Tumors (GISTs)–A Retrospective Analysis

Background Gastrointestinal stromal tumors (GISTs) are the most common gastrointestinal mesenchymal neoplasms which can arise from any part of the gastrointestinal tract (GIT) or an extraintestinal location. Size and the organ of origin are the major imaging inputs expected from the radiologist. However, it is worthwhile to find out which imaging characteristics on MDCT correlate with risk stratification. This knowledge would help the clinician in treatment planning and prognostication. The aim of this retrospective study is to evaluate the various MDCT imaging characteristics of GISTs and find out which parameters have significant association with risk and subsequent development of metastasis on follow-up whenever it was possible.

Materials and Methods This is a retrospective study conducted on 45 histopathologically proven cases of GIST from two institutions by searching from the digital archives. The following imaging parameters were analyzed: maximum size in any plane, organ of origin, shape (round, ovoid or irregular), margin (well-defined or ill-defined), surface (smooth or lobulated), percentage of necrosis, growth pattern, enhancement characteristics–both intensity (mild, moderate or significant) and pattern (homogenous vs. heterogenous), calcification, infiltration into adjacent organs, and presence of metastasis at presentation or on follow-up.

Results CT morphological parameters of significance in risk stratification as per our study include tumor necrosis, predominant cystic change, irregular and lobulated shape/surface characteristics, and adjacent organ infiltration.

The parameters which were associated with development of metastasis were size > 5 cm, necrosis > 30%, and the presence of adjacent organ infiltration.

Conclusion The radiologist has an important role in ascertaining the size of tumor as well as the organ of origin accurately to guide the clinician in risk calculation and subsequent prognostication. In addition, certain CT characteristics mentioned above, namely, tumor size, significant necrosis/cystic changes, irregular/lobulated contour, and invasion of adjacent organs, help in risk stratification and in predicting metastasis/poor prognosis.

The Outcome of Neoadjuvant Imatinib Therapy Combined With Surgery for Rectal Gastrointestinal Stromal Tumors: A Report of Three Cases and a Review of the Literature

Gastrointestinal stromal tumors (GISTs) represent the most frequent mesenchymal tumors of the gastrointestinal tract. They occur most frequently in the stomach. Rectal localization remains rare and represents only 5% of all GIST cases and 0.1% of all rectal tumors. Immunohistochemical staining (CD117, DOG1) and molecular analysis remain the gold standard for diagnosis; DOG1 represents a very sensitive marker regardless of CD117 expression. Complete en-bloc resection constitutes the only curative treatment; however, surgical management of rectal GIST remains challenging and can involve extensive surgery such as abdominoperineal resection with significant morbidity. The role of neoadjuvant Imatinib therapy in rectal GISTs is controversial and mainly indicated in a locally advanced tumor or sphincter invasion to increase the chance of complete resection and sphincter preservation. Herein, we report three cases of a rectal GIST treated with neoadjuvant Imatinib therapy and who underwent extensive surgery with complete resection (R0), as well as a recent review of the literature, to study clinicopathological features, surgical challenges, and perioperative Imatinib therapy outcome of rectal GISTs.

Comparison of characteristic computed tomographic findings of gastrointestinal and non-gastrointestinal stromal tumors in the small intestine

PURPOSE

We aimed to reveal specific findings of gastrointestinal stromal tumors (GISTs) in the small intestine on contrast-enhanced computed tomography (CT) by comparing GISTs with non-GISTs.

METHODS

We enrolled 28 patients with 39 GISTs and 20 patients with 22 non-GISTs who underwent enterectomy with a preoperative diagnosis of small intestinal tumor. All lesions were diagnosed by histopathological examination. Two radiologists independently evaluated internal homogeneity, growth pattern, calcification, intratumoral hemorrhage, degeneration, ulceration, and lymphadenopathy and measured the maximum diameter of the tumor and contrast-enhanced CT (CECT) value of the solid portion as well as the diameter and CT value of the feeding artery and drainage vein on CECT in the arterial and venous phases.

RESULTS

Intratumoral hemorrhage was seen in 15.4% and 25.6% of GISTs and in 0% and 0% of non-GISTs (p = 0.079 and 0.010), with good interobserver agreement (κ = 0.715). The drainage vein diameter correlated well with the maximum diameter of the tumor (r = 0.744, p < 0.001). The CT value of the solid tumor part in the arterial and venous phases (p < 0.01) and the CT value of the drainage vein in the arterial phase (p < 0.05) were higher for GISTs than for non-GISTs (p < 0.01).

CONCLUSIONS

Strong parenchymal enhancement with the peak in the arterial phase and the CT value of the drainage vein in the arterial phase was characteristics findings of GIST compared with non-GISTs. The diameter of the drainage vein was proportional to the maximum diameter of GISTs.

Clinicopathological and morphological spectrum of gastrointestinal stromal tumours on multi-detector computed tomography

Purpose

To describe the clinicopathological and morphological features of gastrointestinal stromal tumours (GISTs) on multi-detector computed tomography (MDCT).

Material and methods

MDCT (plain and post contrast) images of 25 confirmed cases of GISTs were retrospectively evaluated from our hospital database. The images were analysed for the location, size, growth pattern, attenuation pattern, relation to adjacent structures, presence or absence of ulceration, calcification, metastases, lymphadenopathy, and for any complications such as haemorrhage, intestinal obstruction, etc. Institutional Ethics Committee clearance was obtained prior to the commencement of the study. Statistics used included percentage frequency.

Results

Our study group comprised 14 males and 11 females. The mean age of our study population was 60 years (age range: 40 to 82 years). The mean tumour size was 11.7 cm. The stomach and small bowel accounted for 76% of the primary tumour site. The commonest imaging appearance of GIST observed in our study was that of an exophytic mass (76%) with a heterogenous pattern of enhancement (96%) with intratumoural necrosis (76%). MDCT demonstrated complications in three patients (12%). Six patients presented with metastatic foci (five to the liver and one to the lung), while lymphadenopathy was observed in five patients (20%). Associated complications included intestinal obstruction (8%) and retrogastric haematoma (4%). Incidental findings included uterine fibroid (n = 1), ovarian dermoid (n = 1), and chronic pancreatitis (n = 1).

Conclusions

GISTs are predominantly large tumours with a well circumscribed and exophytic pattern on MDCT, with or without cystic/necrotic areas, and they mostly show a heterogenous pattern of enhancement on post-contrast administration.

Reproducible imaging features of biologically aggressive gastrointestinal stromal tumors of the small bowel

PURPOSE

To identify reproducible CT imaging features of small bowel gastrointestinal stromal tumors (GIST) that are associated with biologic aggressiveness.

METHODS

Patients with histologically proven small bowel GISTs and CT enterography or abdominopelvic CT were included. Biologic aggressiveness was established based on initial histologic grading (very low risk to malignant), with "malignant" assigned if recurrence or metastases developed subsequently. CT exams were independently evaluated by three gastrointestinal radiologists for tumor size, growth pattern, enhancement, tumor borders, necrosis, calcification, ulceration, multiplicity, internal air or enteric contrast, nodal metastasis, liver metastasis, peritoneal metastasis, ascites, and draining vein size. Inter-observer variability and imaging features associated with high-grade and malignant small bowel GISTs were determined.

RESULTS

Of 78 patients with small bowel GISTs, 10/78 (13%) were high grade and 18/78 (23%) were malignant. There was moderate to substantial inter-observer agreement (Kappa > 0.4) for all findings except tumor border, ulceration, and nodal metastases. Tumor size, irregular or invasive tumor border, necrosis, liver metastasis, ascites, and iso-enhancement were associated with high-grade/malignant small bowel GISTs (p < 0.04). Internal air or enteric contrast and peritoneal metastases additionally predicted malignant behavior (p < 0.03). When imaging features predicting malignant small bowel GISTs were absent and size was ≤ 3 cm, 0% (0/16), 5% (1/19), and 5% (1/17) of patients had high grade, and 0% (0/16, 0/19, and 0/17) had malignant tumors for the three readers, respectively.

CONCLUSION

Multiple, reproducibly identified, small bowel GIST imaging features suggest biologic aggressiveness. The absence of these imaging features may identify small tumors that can be followed in asymptomatic or high-risk patients.

Impact of CT enterography on the diagnosis of small bowel gastrointestinal stromal tumors

OBJECTIVE

Our purpose is to determine the impact of CT enterography on small bowel gastrointestinal stromal tumor (GIST) detection and biologic aggressiveness, and to identify any imaging findings that correlate with biologic aggressiveness.

METHODS

Records of patients with histologically confirmed small bowel GISTs who underwent CT imaging were reviewed. Biologic aggressiveness was based on initial histologic grading (very low, low, intermediate, high grade; or malignant), with upgrade to malignant category if local or distant metastases developed during clinical follow-up. Imaging indications, findings, and type of CT exam were compared with the biologic aggressiveness.

RESULTS

111 small bowel GISTs were identified, with suspected small bowel bleeding being the most common indication (45/111; 40.5%). While the number of malignant GISTs diagnosed by CT remained relatively constant (2-3 per year), the number of non-malignant GISTs increased substantially (mean 1.5/year, 1998-2005; 8.4/year, 2006-2013). In patients with suspected small bowel bleeding, CT enterography identified 33 GISTs (7/33, 21% malignant) compared to 12 GISTs by abdominopelvic CT (6/12, 50% malignant; p < 0.03). Tumor size (p < 0.0001), internal necrosis (p = 0.005), internal air or enteric contrast (p ≤ 0.021), and ulceration (p ≤ 0.021) were significantly associated with high-grade and malignant tumors, and irregular or invasive tumor borders (p < 0.01) was associated with malignant tumors.

CONCLUSION

The detection of small bowel GISTs can increase due to the use of CT enterography in patients with suspected small bowel bleeding. The large majority of small bowel GISTs detected by CT enterography are not malignant.

Gastrointestinal stromal tumour (GIST) presenting as a strangulated inguinal hernia with small bowel obstruction

Gastrointestinal stromal tumours (GISTs) can arise everywhere along the gastrointestinal (GI) tract. Their presentation in unusual locations should always be taken into account. A 74-year-old man referred to the emergency department for small bowel obstruction caused by an incarcerated inguinal hernia. A CT scan showed a mesenchymal tumour originating from the herniated bowel loop and a mass in the ascending colon. Laparoscopic resection of the mass and laparoscopic right hemicolectomy were performed. The histology showed a ruptured GIST arising from the herniated small bowel and a high-grade dysplasia villous adenoma of the right colon. GISTs can present with symptoms spanning from vague abdominal discomfort to surgical urgencies. Strangulated hernia is an extremely rare presentation, with only two cases described in the literature. A safe surgical approach was obtained with laparoscopy, maintaining surgical radicality. The ileal localisation and the pseudocapsule rupture were the main risk factors on prognostic stratification.

Gastrointestinal stromal tumours (GISTs): an insight into clinical practice with review of literature

BACKGROUND

Gastrointestinal stromal tumours (GISTs) are rare mesenchymal tumours of the gastrointestinal tract. We retrospectively reviewed the clinical management of all patients with GIST presenting to a regional multidisciplinary upper gastrointestinal cancer group in the north of England.

METHODS

Clinical, pathological, immunohistochemical treatment strategies, follow-up and outcome data on all patients with GIST between 2007 and 2012 were reviewed. Tumours were categorised by risk according to the National Institutes of Health (NIH) and AFIP models.

RESULTS

36 (85.7%) of 42 tumours were located in the stomach, 5 (11.9%) in the small intestine and 1 (2.4%) in the oesophagus. Median age of patients was 68 (range 43-91) years. 24 patients (57.1%) were female. Tumour size ranged from 1.0  to 12.7 cm with mean size of 5.46 cm. Metastasis was present in 19 (45.2%) patients at diagnosis with distant metastases in 12 patients. Liver was the most common site of metastases. Histology and immunohistochemical analysis was available in 32 (76.2%) patients. Most common histology was spindle cell morphology 17/32 (53.1%) followed by epithelioid 9/32 (28.1%) and mixed morphology 5/32 (15.6%). The positive rate for KIT protein (CD117) was 90.6%, while that for CD34 was 75.0%. 12/25 (48.0%) and 8/23 (34.8%) patients were categorised as high risk as per NIH and AFIP risk scores, respectively. 23/42 (54.8%) patients underwent surgical resection, after which 5/23 (21.7%) had adjuvant imatinib therapy. Imatinib was given as primary therapy in 14/42 (33.3%) patients.

CONCLUSIONS

Surgery alone may not be a curative treatment for GISTs. Targeted therapy with imatinib may play an important role in the treatment of GISTs. Further risk categorisation models may be needed to evaluate GIST behaviour and prognosis.

Holes in gastric mucosa in upper gastrointestinal endoscopy

Gastritis cystica profunda (GCP) is a rare disease that shows multiple cystic gastric glands dispersed within the submucosa of the stomach. GCP occurs most commonly in patients who have undergone previous gastric surgery and presents as subepithelial tumor or a polypoid lesion. Here, we report the case of GCP in a 79-year-old patient who had undergone Billroth II gastric resection. During upper gastrointestinal endoscopy multiple lesions like tiny holes in the mucosa were observed. Endoscopic ultrasound showed cystic structures in the gastric submucosa. Biopsies finally proved the dispersed mucosal glands in the submucosa, which are pathognomonic for GCP. So far, in all published cases, GCP presented as polypoid lesions with no mucosal damage in upper gastrointestinal endoscopy. It is for the first time that GCP has been diagnosed with cystic lesions connected to the gastric lumen with a porus in each of the cysts.

Molecular imaging of tumor-associated angiogenesis using a novel magnetic resonance imaging contrast agent targeting αvβ 3 integrin

BACKGROUND

The recent introduction of biological anticancer therapy has renewed the interest in functional imaging of tumor-associated angiogenesis (TAA) as a tool to monitor early therapy response. The present study evaluated imaging of TAA using P1227, a novel, small molecular magnetic resonance imaging (MRI) probe targeting αvβ3 integrin.

METHODS

HT29 human colorectal cancers were grown in athymic mice. Dynamic MRI was performed using a three-dimensional VIBE sequence up to 110 min after injection of P1227 or gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA). Specificity was assessed by using P1227 1 h after intravenous administration of the αvβ3 inhibitor cilengitide. Regions of interest were drawn encompassing the tumor rim and normal muscle. Imaging data were compared with microvessel density and αvβ3 expression.

RESULTS

Using P1227, specific enhancement of the angiogenic tumor rim, but not of normal muscle, was observed, whereas Gd-DOTA enhanced tumor and normal muscle. After administering cilengitide, enhancement with P1227, but not with DOTA, was significantly suppressed during the first 20 min. When using P1227, a significant correlation was observed between normalized enhancement of the tumor rim and immunohistochemical αvβ3 integrin expression.

CONCLUSIONS

Molecular MRI using a small monogadolinated tracer targeting αvβ3 integrin and moderate magnetic field strength holds promise in assessing colorectal TAA.

PET-Negative Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal malignancy of the gastrointestinal tract. PET/CT is a common diagnostic tool and is also used for therapy monitoring. GISTs typically show strong ¹⁸F-fluorodeoxyglucose (FDG) uptake. Here we present two cases of GIST with unusually low/negative FDG uptake. FDG negativity does not preclude the diagnosis of a GIST.

Patterns of recurrence of gastrointestinal stromal tumour (GIST) following complete resection: implications for follow-up

AIM

To determine the frequency, time course and sites of recurrence following surgical resection of gastrointestinal stromal tumours (GIST) and to evaluate the performance of a risk-based surveillance protocol in detection of recurrence.

METHODS

Eighty-one patients on surveillance following complete resection of GIST were included. Patients were stratified into risk groups according to accepted histopathological criteria. Computed tomography (CT) examinations were retrospectively reviewed to determine rates, sites and imaging characteristics of recurrence and to assess compliance with the local follow-up protocol.

RESULTS

The median time of follow-up was 41 months. Nineteen patients suffered recurrence, all of whom were in the high-risk group. Fifty-eight percent of relapses occurred within 1 year and 84% within 3 years. Even within the high-risk group, patients with relapse had significantly larger (mean 15 versus 10.4 cm, p < 0.05) and more mitotically active primary tumours (mean 33.7 versus 5.6 mitoses per 50 high-power fields; p < 0.05) than those with no relapse. Relapse was to the liver in 12 cases (63%) and to the omentum and mesentery in nine cases (47%), and was asymptomatic in three-quarters of patients.

CONCLUSIONS

The high incidence of GIST recurrence in the high-risk group in the first 3 years after surgery supports the use of intensive imaging surveillance in this period. Relapse is often asymptomatic and commonly occurs to the liver, omentum and mesentery. Stratification by tumour factors may enable improved tailoring of surveillance protocols within the high-risk group in the future.

A rare giant gastrointestinal stromal tumor of the stomach traversing the upper abdomen: a case report and literature review

We present the case of a 66-year-old woman with a huge gastrointestinal stromal tumor of the stomach that traversed her upper abdomen. The predominant abdominal sign was a huge, palpable mass, but there were no other distinctive findings in her physical examination or her routine blood workup, including biochemical markers. It was difficult to judge the origin of the mass upon imaging. Furthermore, radiological findings revealed that the mass had a complex relationship with many major blood vessels. An exploratory laparotomy revealed a huge tumor protruding from the anterior wall of the stomach fundus, on the lesser curvature of the stomach, measuring approximately 21 × 34 × 11 cm in diameter and weighing 5.5 kg. A complete resection was performed and the tumor was characterized on immunohistochemistry as a gastrointestinal stromal tumor of the stomach. Preoperative diagnosis of gastrointestinal stromal tumors can be difficult, and we hope that the presentation of this rare case and literature review will benefit other diagnosing clinicians having similar problems.

Intratumoral heterogeneity of F-18 FDG uptake differentiates between gastrointestinal stromal tumors and abdominal malignant lymphomas on PET/CT

OBJECTIVE

Gastrointestinal stromal tumors (GISTs) and malignant lymphomas (MLs) in the abdomen are often observed as tumors of unknown origin on F-18 FDG PET/CT. The purpose of this study was to evaluate the intratumoral metabolic heterogeneity of F-18 FDG uptake on PET to determine if it might be helpful to discriminate between these tumors.

METHODS

The F-18 FDG PET/CT findings of 21 large abdominal tumors were retrospectively evaluated (9 GISTs and 12 MLs). Intratumoral heterogeneity was evaluated by visual scoring (visual score: 0, homogeneous; 1, slightly heterogeneous; 2, moderately heterogeneous; 3, highly heterogeneous) and by the cumulative standardized uptake value (SUV) histograms on transaxial PET images at the maximal cross-sectional tumor diameter. Percent tumor areas above a threshold from 0 to 100% of the maximum SUV were plotted and the area under curve of the cumulative SUV histograms (AUC-CSH) was used as a heterogeneity index, where lower values corresponded with increased heterogeneity. Correlation between the visual score and the AUC-CSH was investigated by the Spearman's rank test.

RESULTS

GISTs exhibited heterogeneous uptake of F-18 FDG, whereas MLs showed rather homogeneous uptake on visual analysis (visual score: 2.67 ± 0.50 and 0.58 ± 0.79, respectively; p < 0.001). The AUC-CSH was significantly lower for the GISTs than for the MLs (0.41 ± 0.14 and 0.64 ± 0.08, respectively; p < 0.001). Significant correlations were observed between the visual score and the AUC-CSH (ρ = -0.866, p < 0.001).

CONCLUSION

GISTs exhibited significantly heterogeneous intratumoral tracer uptake as compared with the MLs. Evaluation of the intratumoral heterogeneity of F-18 FDG uptake may help in the discrimination between these tumors.