Beyond CT: A Case Analysis of Serial [18F]FDG PET/CT for Assessment of Necrosis and Early Recurrence in Colorectal Liver Metastases

Colorectal cancer is a common malignancy, with the liver being the most frequent site of metastases. [18F] Fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) has emerged as a valuable tool in detecting and evaluating liver metastases and extrahepatic disease. Herein, we present a case of a 76-year-old male with colorectal cancer associated with lung and liver metastases. The patient received 12 chemoimmunotherapy cycles and was then put on maintenance cetuximab; serial [18F]FDG PET/CT scans were utilized to evaluate treatment response. The patient exhibited a positive response to chemoimmunotherapy, with regression of rectal disease and resolution of pulmonary metastatic nodules. Serial [18F]FDG PET/CT scans unveiled three distinct necrotic patterns. The case report advocates that [18F]FDG PET/CT plays an important role in evaluating colorectal liver metastases (CRLM) response to treatment, identifying transient necrosis, early recurrence, and emphasizing the limitations of post-treatment CT scans in identifying early CRLM recurrence. Integrating functional imaging, particularly [18F]FDG PET/CT, promises for management monitoring and surveillance of CRLM patients.

Colorectal liver metastases: radiopathological correlation

With the development of chemotherapy regimens, targeted therapies, and hepatic surgery, the survival of patients with colorectal liver metastases (CRLM) has dramatically improved. Imaging plays a central role for the diagnosis, staging, and treatment allocation in these patients. To interpret CRLM on imaging, radiologists must be familiar with the main imaging features of untreated tumors as well as the modifications induced by systemic therapies, and their meaning in relation to pathological tumor response and tumor biology. CRLM have the same histological features as the primary tumor. Most are “non-otherwise specified” (NOS) adenocarcinomas. The mucinous tumor is the most common of the rare subtypes. In NOS tumors, imaging usually differentiates central areas of necrosis from peripheral proliferating tumors and desmoplastic reaction. Areas of mucin mixed with fibrosis are seen in mucinous subtypes to help differentiate the metastases from other tumors cysts or hemangiomas. After treatment, the viable tumor is gradually replaced by ischemic-like necrosis and fibrosis, and remnants cells are mainly located on the periphery of tumors. Imaging can help predict the degree of tumor response, but changes can be difficult to differentiate from the pretherapeutic appearance. When chemotherapy is interrupted or in case of resistance to treatment, a peripheral infiltrating halo of tumor growth may appear. The purpose of the article is to illustrate the significance of the imaging features of colorectal liver metastases during systemic therapy, using radiopathological correlations.

My approach to endoscopic ultrasound-guided fine-needle aspiration biopsy specimens of the pancreas

Endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNAB) is the optimal method for sampling lesions of the pancreas. This procedure is being performed at increasing numbers of hospitals and therefore, more and more cellular pathology departments are having to process and report EUS-FNAB specimens. This article outlines the advantages of using tissue/cell block preparation to process these specimens. In particular, such preparation concentrates, conserves and preserves sampled material which is then available for a full array of further analyses. Tissue/cell block preparation also enables EUS-FNAB specimens to be assessed by a wider range of cellular pathologists. This article demonstrates how a tissue/cell block protocol permits the diagnosis of the full range of pancreatic pathologies sampled by EUS-FNAB. The protocol is identical for all these pathologies (including both solid and cystic lesions) and is simple at all stages of the specimen pathway, from collection to processing to assessment.

Aberrant expression of OATP1B3 in colorectal cancer liver metastases and its clinical implication on gadoxetic acid-enhanced MRI

Purpose

To investigate the factors associated with hepatobiliary phase (HBP) enhancement at gadoxetic acid-enhanced magnetic resonance imaging (MRI) and to determine whether HBP images could be used to predict prognosis in patients with colorectal cancer liver metastasis (CRLM).

Results

Of the 96 total nodules, 65 and 31 nodules were in the mixed and clearly hypointense groups, respectively. In the 55 nodules without preoperative chemotherapy, organic anionic transporting polypeptide 1B3 (OATP1B3) expression was a significant factor regarding the HBP enhancement (P=0.042). In this subgroup, nodules with OATP1B3 expression displayed a significantly higher relative intensity ratio on the HBP image (RIR_post) and relative enhancement ratio (RER) than those lacking this marker (P=0.024, 0.003, respectively). No significant factor was associated with the enhancement pattern in the chemotherapy group. The mixed hypointense group displayed worse survival rates (P=0.002).

Materials and Methods

Ninety-six patients who underwent pre-operative liver MRI and surgical resection for CRLM from January 2010 to June 2012 were retrospectively analyzed. We qualitatively evaluated the HBP enhancement pattern of CRLMs and classified them into mixed and clearly hypointense groups. For quantitative measurement, the RIR_post and RER were analyzed. To investigate factors associated with HBP enhancement, tumor components (fibrosis, necrosis, and cellularity) and OATP1B3 expression were scored on a 4-point scale. Univariate and multivariate analyses were done to determine significant factors for visual enhancement and quantitative parameters.

Conclusions

OATP1B3 expression is associated with mixed hypointense CRLMs without chemotherapy. Signal intensity on HBP has potential usefulness to predict prognosis in CRLMs.

Gadoxetic acid-enhanced 3.0T MRI for the evaluation of hepatic metastasis from colorectal cancer: metastasis is not always seen as a "defect" on the hepatobiliary phase

PURPOSE

To determine specific imaging features of hepatic metastasis from colorectal cancer, focusing on the hepatobiliary phase (HBP) of gadoxetic acid-enhanced MRI.

MATERIALS AND METHODS

Over a 2-year period, 79 hepatic metastatic lesions were identified from 32 patients (22 men and 10 women) who proven colorectal cancer and underwent gadoxetic acid-enhanced 3.0T MRI. Hepatic metastases were proven pathologically in 16 patients: by surgical liver resection (n=14) and by US-guided biopsy (n=2). The remaining 16 patients were considered to have hepatic metastasis based on imaging studies and clinical information. Two radiologists evaluated the imaging features of each MRI sequence, including high resolution T2WI, dynamic contrast enhancement study with hepatobiliary phase, and diffusion weighted image. We also compared SI of the lesions on T2WI and HBP.

RESULTS

T2WI showed homogeneous high SI (n=25; 31.7%), target appearance (n=3; 3.8%), reversed target appearance (n=2; 2.6%), and heterogeneously high SI (n=49; 62%). On HBP, homogeneous defect were seen in 22 lesions (27.9%), target appearance in five lesions (6.4%), reversed target appearance in two lesions (2.5%), and heterogeneous defect in 50 lesions (63.3%); including reticular (70%), partially globular (26%), and diffuse GGO-like (4%) patterns. According to the imaging features on HBP, the homogeneous defect and heterogeneous defect groups had a mean ADC value of 0.99 × 10(-3) and 1.07 × 10(-3)mm(2)/s, respectively, without statistically significant difference.

CONCLUSION

Hepatic metastasis from colorectal cancer usually showed as a heterogeneous defect on HBP and a heterogeneous high SI on T2WI. The generally accepted "true defect" was not a common finding in hepatic metastasis from colorectal cancer.

MR imaging correlates of intratumoral tissue types within colorectal liver metastases: a high-spatial-resolution fresh ex vivo radiologic-pathologic correlation study

PURPOSE

To analyze the direct relationship between complex internal magnetic resonance (MR) signal intensity (SI) patterns observed in colorectal liver metastases and their microscopic tissue characteristics.

MATERIALS AND METHODS

The institutional ethics board approved this study. In seven consecutive patients undergoing hepatic resection for liver metastases (primary colorectal in six, breast mistaken for colorectal in one), the resected fresh ex vivo liver specimen was examined with T1-weighted (repetition time msec/echo time msec, 9/4.4-4.8) and T2-weighted (2500/90) MR imaging by using a voxel size of 0.47 x 0.7 x 2 mm. The liver was sectioned in a concordant plane, and individual histologic slides were scanned and reconstructed to form a whole-mount pathologic image of the metastases. A pathologist identified the regions of interest for intraacinar necrosis (IAN), loose or dense fibrosis, and moderately and poorly differentiated cells within the metastases, and these regions were matched to the corresponding MR image. The morphologic and SI patterns were noted. The normalized ratio between the SI of these regions and that of the background liver was determined on T1- and T2-weighted images. Pairwise differences between tissue types were calculated by using linear mixed model, with the P values adjusted for multiple comparisons by using the method of Sidak.

RESULTS

A total of 98 zones were defined after pathologic analysis. On T2-weighted images, IAN was significantly lower in SI (P < .05) than the other tissues types. On T1-weighted images, IAN was significantly higher in SI than the other tissues types (P < .001). The type of necrosis encountered in these specimens was exclusively IAN. Qualitatively IAN had a specific pattern of SI (hypointense on T2-weighted and hyperintense on T1-weighted images). Other tissues types, including fibrosis, showed a pattern of hyperintensity on T2-weighted and hypointensity on T1-weighted images.

CONCLUSION

IAN seen in colorectal metastases exhibits high T1-weighted SI and mixed T2-weighted SI. This SI pattern is unusual for common benign liver lesions and may be helpful in the MR imaging diagnosis of colorectal liver metastases. (c) RSNA, 2010.