Sinonasal cancer in The Netherlands: Follow-up of a population-based study 1989-2014 and incidence of occupation-related adenocarcinoma.

BACKGROUND: Long-term trends of sinonasal cancer in The Netherlands have been investigated with particular attention on adenocarcinoma for which wood or leather dust is a well-known risk factor. METHODS: All 4345 patients (1989-2014) registered in the Netherlands Cancer Registry were included. Standardized 3-year moving incidence rates per 1 000 000/person-years, and estimated annual percentage change (EAPC) were calculated. RESULTS: Forty-seven percent of the patients had squamous cell carcinoma (SCC), 12% had lymphoma, and 12% had adenocarcinoma. Sixty-one percent of the tumors were located in the nasal cavity, 22% in the maxillary, and 11% in the ethmoidal sinus. Male incidence decreased to 11.5/1 000 000 due to less SCC (EAPC -0.9%; 95% confidence interval [CI] -1.6 to 0.3) and adenocarcinoma (EAPC -4.3%; 95% CI -5.5 to 3.1). Female incidence increased to 7/1 000 000 (EAPC +2.0%; 95% CI +1.1 to +3.0) due to more SCC (EAPC +2.2%; 95% CI +1.0 to +3.5), whereas adenocarcinoma remained stable (0.6/1 000 000; EAPC +1.1%; 95% CI -6.0 to +8.7). Tumors of the nasal cavity increased in women (EAPC +3.3%; 95% CI +2.0 to 4.7). CONCLUSION: The decrease of male sinonasal adenocarcinoma may be the result of preventive measures combined with less workers in high-risk occupations.

Digital Video Laryngoscopy and Flexible Endoscopic Biopsies as an Alternative Diagnostic Workup in Laryngopharyngeal Cancer: A Prospective Clinical Study.

OBJECTIVES: An office-based workup strategy for patients with laryngopharyngeal lesions suspicious for carcinoma is analyzed. The feasibility of office-based transnasal flexible endoscopic biopsies under local anesthesia and the impact on the diagnostic workup are evaluated. METHODS: This study is a prospective analysis of patients with laryngeal, oropharyngeal, and hypopharyngeal lesions suspicious for carcinoma. One hundred eighty-eight participants were divided into 2 groups. The first group underwent an office-based biopsy procedure under local anesthesia using a flexible digital video laryngoscope with instrument channel (n = 53), and the second group underwent a biopsy procedure under general anesthesia using rigid laryngopharyngoscopy (n = 135). RESULTS: Office-based flexible endoscopic biopsies were tolerated well, and there were no complications. These biopsies were 92.5% successful in acquiring a definitive diagnosis. Costs were reduced. Diagnostic workup time and time until start of therapy were reduced to 2 days and 27 days, respectively. CONCLUSION: Office-based biopsy under local anesthesia using flexible digital video laryngoscopy is safe, cost-effective, and successful in providing a histopathological diagnosis. It reduces the diagnostic workup time significantly in patients with laryngeal, oropharyngeal, and hypopharyngeal cancer, while also reducing the necessity to subsequently perform a rigid laryngopharyngoscopy under general anesthesia.

The role of systemic therapy in the management of sinonasal cancer: A critical review.

PURPOSE: Due to the rarity and the variety of histological types of sinonasal cancers, there is a paucity of data regarding strategy for their optimal treatment. Generally, outcomes of advanced and higher grade tumors remain unsatisfactory, despite the employment of sophisticated surgical approaches, technical advances in radiation techniques and the use of heavy ion particles. In this context, we critically evaluated the role of systemic therapy as part of a multidisciplinary approach to locally advanced disease. RESULTS: Induction chemotherapy has shown encouraging activity and could have a role in the multimodal treatment of patients with advanced sinonasal tumors. For epithelial tumors, the most frequently employed chemotherapy is cisplatin, in combination with either 5-fluorouracil, taxane, ifosfamide, or vincristine. Only limited experiences with concurrent chemoradiation exist with sinonasal cancer. The role of systemic treatment for each histological type (intestinal-type adenocarcinoma, sinonasal undifferentiated carcinoma, sinonasal neuroendocrine carcinoma, olfactory neuroblastoma, sinonasal primary mucosal melanoma, sarcoma) is discussed. CONCLUSIONS: The treatment of SNC requires a multimodal approach. Employment of systemic therapy for locally advanced disease could result in better outcomes, and optimize the therapeutic armamentarium. Further studies are needed to precisely define the role of systemic therapy and identify the optimal sequencing for its administration in relation to local therapies.

Pathology-based validation of FDG PET segmentation tools for volume assessment of lymph node metastases from head and neck cancer.

PURPOSE: FDG PET is increasingly incorporated into radiation treatment planning of head and neck cancer. However, there are only limited data on the accuracy of radiotherapy target volume delineation by FDG PET. The purpose of this study was to validate FDG PET segmentation tools for volume assessment of lymph node metastases from head and neck cancer against the pathological method as the standard. METHODS: Twelve patients with head and neck cancer and 28 metastatic lymph nodes eligible for therapeutic neck dissection underwent preoperative FDG PET/CT. The metastatic lymph nodes were delineated on CT (NodeCT) and ten PET segmentation tools were used to assess FDG PET-based nodal volumes: interpreting FDG PET visually (PETVIS), applying an isocontour at a standardized uptake value (SUV) of 2.5 (PETSUV), two segmentation tools with a fixed threshold of 40% and 50%, and two adaptive threshold based methods. The latter four tools were applied with the primary tumour as reference and also with the lymph node itself as reference. Nodal volumes were compared with the true volume as determined by pathological examination. RESULTS: Both NodeCT and PETVIS showed good correlations with the pathological volume. PET segmentation tools using the metastatic node as reference all performed well but not better than PETVIS. The tools using the primary tumour as reference correlated poorly with pathology. PETSUV was unsatisfactory in 35% of the patients due to merging of the contours of adjacent nodes. CONCLUSION: FDG PET accurately estimates metastatic lymph node volume, but beyond the detection of lymph node metastases (staging), it has no added value over CT alone for the delineation of routine radiotherapy target volumes. If FDG PET is used in radiotherapy planning, treatment adaptation or response assessment, we recommend an automated segmentation method for purposes of reproducibility and interinstitutional comparison.

Aggressive fibromatosis in the head and neck region: Benign tumor with often mutilating effects.

BACKGROUND: Aggressive fibromatosis (AF) or desmoid tumor of the head and neck region is a rare, usually unresectable, benign soft tissue tumor with locally aggressive behavior. METHODS AND RESULTS: A 31-year-old woman presented with a progressive trismus, a swelling in the retromandibular area, as well as loss of sensibility of the maxillary and mandibular branch of the trigeminal nerve. MRI of the head and neck revealed an infiltrative mass involving the masticator, parapharyngeal, and prevertebral and paravertebral space on the left with intracranial extension through the orbital fissure. After the fifth biopsy, 15 months after presentation, the diagnosis of AF was made. The tumor was unresectable, so intensity-modulated radiotherapy was given with curative intent using a total dose of 60 Gy in 30 fractions of 2 Gy. After 16 months, she showed progressive disease, for which tamoxifen 40 mg twice daily was started with a good response for 2 years. After that, she started with sorafinib, on which she has stable disease now. CONCLUSION: The often long delay in proper diagnosis and the treatment challenges of a desmoid tumor are illustrated in this case. Furthermore, this article reviews the literature concerning AF, especially of the head and neck region.

Novel diagnostic modalities for assessment of the clinically node-negative neck in oral squamous-cell carcinoma.

Oral squamous-cell carcinomas arise in mucosal linings of the oral cavity and frequently metastasise to regional lymph nodes in the neck. The presence of nodal metastases is a determinant of prognosis and clinical management. The neck is staged by palpation and imaging, but accuracy of these techniques to detect small metastases is low. In general, 30-40% of patients will have occult nodal disease and will develop clinically detectable lymph-node metastases when the neck is left untreated. The choice at present is either elective treatment or careful observation followed by treatment of the neck in patients who develop manifest metastases. These unsatisfying therapeutic options have been the subject of debate for decades. Recent developments in staging of the neck, including expression profiling and sentinel lymph-node biopsy, will allow more personalised management of the neck.

Validation of a gene expression signature for assessment of lymph node metastasis in oral squamous cell carcinoma.

PURPOSE: Current assessment of lymph node metastasis in patients with head and neck squamous cell carcinoma is not accurate enough to prevent overtreatment. The aim of this study was validation of a gene expression signature for distinguishing metastasizing (N+) from nonmetastasizing (N0) squamous cell carcinoma of the oral cavity (OSCC) and oropharynx (OPSCC) in a large multicenter cohort, using a diagnostic DNA microarray in a Clinical Laboratory Improvement Amendments/International Organization for Standardization-approved laboratory. METHODS: A multigene signature, previously reported as predictive for the presence of lymph node metastases in OSCC and OPSCC, was first re-evaluated and trained on 94 samples using generic, whole-genome, DNA microarrays. Signature genes were then transferred to a dedicated diagnostic microarray using the same technology platform. Additional samples (n=222) were collected from all head and neck oncologic centers in the Netherlands and analyzed with the diagnostic microarray. Human papillomavirus status was determined by real-time quantitative polymerase chain reaction. RESULTS: The negative predictive value (NPV) of the diagnostic signature on the entire validation cohort (n=222) was 72%. The signature performed well on the most relevant subset of early-stage (cT1-T2N0) OSCC (n=101), with an NPV of 89%. CONCLUSION: Combining current clinical assessment with the expression signature would decrease the rate of undetected nodal metastases from 28% to 11% in early-stage OSCC. This should be sufficient to enable clinicians to refrain from elective neck treatment. A new clinical decision model that incorporates the expression signature is therefore proposed for testing in a prospective study, which could substantially improve treatment for this group of patients.

Survival analysis of head and neck squamous cell carcinoma: influence of smoking and drinking.

BACKGROUND: Head and neck squamous cell carcinomas (HNSCCs) are associated with tobacco and alcohol; however, the prognostic relevance of these substances is unclear. METHODS: Univariate and multivariate survival analyses were performed for patients with (n = 1829) and without (n = 183) substance use. RESULTS: HNSCC-specific survival (death due to primary-HNSCC or recurrent HNSCC) and HNSCC/second primary tumor-specific survival (death due to primary-HNSCC or recurrent HNSCC or second primary tumor) were not significantly different for patients who smoked and drank alcohol (hazard ratio [HR], 1.26; 95% confidence interval [CI], 0.86-1.85) and those who did not (HR, 1.34; 95% CI, 0.96-1.88). Overall survival was significantly affected; HR for patients who smoked and drank alcohol was 1.50 (95% CI, 1.16-1.93). CONCLUSION: Although tobacco and alcohol use are the main risk factors for development of HNSCC, disease outcome was comparable in patients who did or did not use these substances. Tobacco and alcohol use affected overall survival, which emphasizes the importance of substance use cessation.

High levels of p53 expression correlate with DNA aneuploidy in (pre)malignancies of the vulva.

The molecular pathogenesis of human papilloma virus-unrelated vulvar squamous cell carcinoma is not well known. Whether malignant progression of lichen sclerosus and differentiated vulvar intraepithelial neoplasia to vulvar squamous cell carcinoma could be accompanied by altered DNA content has not been studied extensively. DNA content in isolated nuclei of microdissected normal vulvar epithelium (n = 2), lichen sclerosus (n = 9), differentiated vulvar intraepithelial neoplasia (n = 13), and squamous cell carcinoma (n = 17) from 22 patients was measured via DNA image cytometry. For additional analysis, 6 differentiated vulvar intraepithelial neoplasia lesions were selected, bringing the number of patients to 28. p53 expression was determined by immunohistochemistry on consecutive tissue sections. Thirty-eight percent (5/13) of differentiated vulvar intraepithelial neoplasia lesions and 65% (11/17) of squamous cell carcinomas were DNA aneuploid or tetraploid. In lesions that contained differentiated vulvar intraepithelial neoplasia and adjacent squamous cell carcinoma, the ploidy status of differentiated vulvar intraepithelial neoplasia did not exceed that of squamous cell carcinoma. We observed a strong correlation between high p53 expression and DNA aneuploidy. This relation was also present at the level of a single nucleus, measured by sequential image cytometry of p53 immunohistochemistry followed by DNA image cytometry on formalin-fixed tissue sections. Similarly, we found p53-positive nonproliferating cells with increased DNA content in the superficial compartment of 6 additional solitary differentiated vulvar intraepithelial neoplasia lesions that were not associated with squamous cell carcinoma, indicating ascending aneuploid cells from the basal compartment. DNA ploidy measurements suggest that differentiated vulvar intraepithelial neoplasia has a higher malignant potential than lichen sclerosus and thus is a more likely precursor of squamous cell carcinoma. Furthermore, high p53 expression correlates with increased DNA content and aneuploidy; but it requires further research to unveil a possible causal relation.

Histopathologic validation of 3'-deoxy-3'-18F-fluorothymidine PET in squamous cell carcinoma of the oral cavity.

UNLABELLED: Accelerated tumor cell repopulation is an important mechanism adversely affecting therapeutic outcome in head and neck cancer. The noninvasive assessment of the proliferative state of a tumor by PET may provide a selection tool for customized treatment. 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) is a PET tracer that is phosphorylated by thymidine kinase 1 (TK-1) and, as such, reflects cellular proliferation. Before the use of (18)F-FLT PET for tumor characterization is accepted and introduced into clinical studies, validation against tumor histology is mandatory. The aim of this study was to validate (18)F-FLT PET in squamous cell carcinomas of the oral cavity using immunohistochemical staining for the proliferation marker iododeoxyuridine and for TK-1. METHODS: Seventeen patients with primary squamous cell carcinomas of the oral cavity underwent an (18)F-FLT PET/CT scan before surgery, and iododeoxyuridine was administered 20 min before tumor resection. (18)F-FLT PET/CT scans were segmented, and PET/CT volumes and PET signal intensities were calculated (mean standardized uptake value [SUV(mean)] and maximum standardized uptake value [SUV(max)]). Multiple paraffin-embedded tumor sections were immunohistochemically stained for iododeoxyuridine and TK-1. For iododeoxyuridine, labeling indices and optical densities were calculated and correlated with SUV(mean) and SUV(max). TK-1 staining was visually and semiquantitatively assessed. RESULTS: All primary tumors were identified with (18)F-FLT PET but with a large range in tracer uptake (mean SUV(max), 5.9; range, 2.2-15.2). Also, there was a large variability in iododeoxyuridine labeling indices (mean, 0.09; range, 0.01-0.29) and optical densities (mean, 28.2; range, 12.6-37.8). The iododeoxyuridine optical densities correlated significantly with SUV(mean) and SUV(max), but the labeling indices did not. In most tumors, TK-1 staining of varying intensity was present but correlated with neither iododeoxyuridine binding nor (18)F-FLT uptake. CONCLUSION: The current study demonstrated only a weak correlation between (18)F-FLT uptake and iododeoxyuridine staining intensity in oral cavity tumors. This weak correlation may be explained by differences in biomarker characteristics, resolution, and quantification methods.

Activated leukocyte cell adhesion molecule expression predicts lymph node metastasis in oral squamous cell carcinoma.

Lymphatic metastasis of oral squamous cell carcinoma (SCC) is important for prognosis and clinical decision making concerning the treatment of the neck but may be difficult to detect. Activated leukocyte cell adhesion molecule (ALCAM), has been shown to correlate with prognosis or tumor grade in different tumor types and may be a predictor of lymphatic metastasis. ALCAM expression at the invasive front in fresh frozen tissue samples of oral SCC's (n=41) was studied immunohistochemically, using a polyclonal antibody directed against ALCAM's extracellular domain. Membranous expression of ALCAM at the invasive front was significantly related to lymph node metastasis (p=0.001, sensitivity 69%, specificity 84%) and tumor grade (p=0.035). There was no significant relationship with tumor thickness (p=0.394). Lymph node status (p=0.030), correlated with 5-year overall survival. A significant relation between ALCAM and prognosis could not be established, due to an insufficient sample size. However, ALCAM expression does appears to increase risk of early death. Membranous ALCAM expression at the invasive front serves as a molecular marker for lymphatic metastasis and may facilitate better treatment choices concerning the neck in patients with oral SCC.

Unilateral condylar hyperactivity: a histopathologic analysis of 47 patients.

PURPOSE: To perform a histopathologic analysis of condyles that were resected because of unilateral condylar hyperactivity and compare the results of the bone scan with the histopathologic findings. PATIENTS AND METHODS: A total of 47 resected condyles were histopathologically examined. In 29 cases, a single photon emission computed tomography (SPECT) bone scan was available. For all condylar specimens, a standardized histologic scoring system was used to assess the number of cartilage islands and the thickness of the cartilage layer. The SPECT scans were analyzed by calculating the difference in bone activity between the hyperactive and contralateral condyles. RESULTS: The number of cartilage islands was highly variable, ranging from almost absent in 37% of the patients to abundant in 35%. Furthermore, the relative thickness of the cartilage layer exhibited considerable variation, from less than one quarter of the total thickness of the condylar articular layer in 22% of the patients to one half of the total thickness in 35%. We found no significant relationship between the number of cartilage islands and bone activity using SPECT (P = .11) or between the relative thickness of the cartilage layer and bone activity using SPECT (P = .82). CONCLUSIONS: Unilateral condylar bone growth can occur without large numbers of cartilage islands and without abundant cartilage formation. The bone activity measured by bone scintigraphy was not related to the histologic results. The histopathologic findings of resected condyles in unilateral condylar hyperactivity cannot, therefore, be used as a reference standard. Nevertheless, histopathologic examination should always be performed to rule out other diseases.

Metastatic potential of an aneurysmal bone cyst.

Aneurysmal bone cysts (ABCs) are benign bone tumors consisting of blood-filled cavities lined by connective tissue septa. Recently, the hypothesis that ABCs are lesions reactive to local hemodynamics has been challenged after the discovery of specific recurrent chromosomal abnormalities. Multiple cases of malignant transformation of ABC into (osteo)sarcoma have been described, as well as a number of cases of telangiectatic osteosarcoma which had been misdiagnosed as ABC. We herewith document a case of a pelvic ABC metastatic to the lung, liver, and kidneys. Diagnosis was confirmed by the presence of a break in the USP6 gene, which is pathognomonic for ABC, in a pulmonary metastasis of our patient. Sarcomatous transformation as an explanation for this behavior was ruled out by demonstrating diploid DNA content in both the pulmonary lesion and the primary tumor.

18F-FLT PET does not discriminate between reactive and metastatic lymph nodes in primary head and neck cancer patients.

UNLABELLED: Repopulation of clonogenic tumor cells is inversely correlated with radiation treatment outcome in head and neck squamous cell carcinomas. A functional imaging tool to assess the proliferative activity of tumors could improve patient selection for treatment modifications and could be used for evaluation of early treatment response. The PET tracer 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) can image tumor cell proliferation before and during radiotherapy, and it may provide biologic tumor information useful in radiotherapy planning. In the present study, the value of (18)F-FLT PET in determining the lymph node status in squamous cell carcinoma of the head and neck was assessed, with pathology as the gold standard. METHODS: Ten patients with newly diagnosed stage II-IV squamous cell carcinoma of the head and neck underwent (18)F-FLT PET before surgical tumor resection with lymph node dissection. Emission (18)F-FLT PET and CT images of the head and neck were recorded and fused, and standardized uptake values (SUVs) were calculated. From all 18 (18)F-FLT PET-positive lymph node levels and from 8 (18)F-FLT PET-negative controls, paraffin-embedded lymph node sections were stained and analyzed for the endogenous proliferation marker Ki-67 and for the preoperatively administered proliferation marker iododeoxyuridine. The sensitivity, specificity, positive predictive value, and negative predictive value were calculated for (18)F-FLT PET. RESULTS: Primary tumor sites were oral cavity (n=7), larynx (n=2), and maxillary sinus (n=1). Nine of the 10 patients examined had (18)F-FLT PET-positive lymph nodes (SUV(mean): median, 1.2; range, 0.8-2.9), but only 3 of these patients had histologically proven metastases. All metastatic lymph nodes showed Ki-67 and iododeoxyuridine staining in tumor cells. In the remaining 7 patients, there was abundant Ki-67 and iododeoxyuridine staining of B-lymphocytes in germinal centers in PET-positive lymph nodes, explaining the high rate of false-positive findings. The sensitivity, specificity, positive predictive value, and negative predictive value of (18)F-FLT PET were 100%, 16.7%, 37.5%, and 100%, respectively. CONCLUSION: In head and neck cancer patients, (18)F-FLT PET showed uptake in metastatic as well as in nonmetastatic reactive lymph nodes, the latter due to reactive B-lymphocyte proliferation. Because of the low specificity, (18)F-FLT PET is not suitable for assessment of pretreatment lymph node status. This observation may also negatively influence the utility of (18)F-FLT PET for early treatment response evaluation of small metastatic nodes.

Dissection of a metastatic gene expression signature into distinct components.

BACKGROUND: Metastasis, the process whereby cancer cells spread, is in part caused by an incompletely understood interplay between cancer cells and the surrounding stroma. Gene expression studies typically analyze samples containing tumor cells and stroma. Samples with less than 50% tumor cells are generally excluded, thereby reducing the number of patients that can benefit from clinically relevant signatures. RESULTS: For a head-neck squamous cell carcinoma (HNSCC) primary tumor expression signature that predicts the presence of lymph node metastasis, we first show that reduced proportions of tumor cells results in decreased predictive accuracy. To determine the influence of stroma on the predictive signature and to investigate the interaction between tumor cells and the surrounding microenvironment, we used laser capture microdissection to divide the metastatic signature into six distinct components based on tumor versus stroma expression and on association with the metastatic phenotype. A strikingly skewed distribution of metastasis associated genes is revealed. CONCLUSION: Dissection of predictive signatures into different components has implications for design of expression signatures and for our understanding of the metastatic process. Compared to primary tumors that have not formed metastases, primary HNSCC tumors that have metastasized are characterized by predominant down-regulation of tumor cell specific genes and exclusive up-regulation of stromal cell specific genes. The skewed distribution agrees with poor signature performance on samples that contain less than 50% tumor cells. Methods for reducing tumor composition bias that lead to greater predictive accuracy and an increase in the types of samples that can be included are presented.

Maintenance of head and neck tumor gene expression profiles upon lymph node metastasis.

Spread of cancer and development of solid metastases at distant sites is the main cause of cancer-related deaths. To understand and treat metastases, it is important to determine at which stages the most pivotal steps for development of metastases occur. In head and neck squamous cell carcinoma (HNSCC), metastasis nearly always occurs first in local lymph nodes before development of distant metastasis. Here, we have investigated gene expression patterns in HNSCC lymph node metastases using DNA microarrays. Several types of analyses show that the gene expression patterns in lymph node metastases are most similar to the corresponding primary tumors from which they arose, as long as samples contain sufficient proportions of tumor cells. Strikingly, gene expression patterns of metastatic primary HNSCC are largely maintained upon spread to the lymph node. Only a single gene, metastasis-associated gene 1 (MTA1), was found to show consistently changed expression between a large number of matched primary tumor-lymph node metastasis pairs. The maintained expression pattern includes the predictive signature for HNSCC lymph node metastasis. These results underscore the importance of the primary tumor gene expression profile for development and treatment of metastasis. The findings also agree with the concept that disseminated cancer cells alter the surrounding tissue into a metastatic environment that resembles the primary tumor microenvironment.

Multiple robust signatures for detecting lymph node metastasis in head and neck cancer.

Genome-wide mRNA expression measurements can identify molecular signatures of cancer and are anticipated to improve patient management. Such expression profiles are currently being critically evaluated based on an apparent instability in gene composition and the limited overlap between signatures from different studies. We have recently identified a primary tumor signature for detection of lymph node metastasis in head and neck squamous cell carcinomas. Before starting a large multicenter prospective validation, we have thoroughly evaluated the composition of this signature. A multiple training approach was used for validating the original set of predictive genes. Based on different combinations of training samples, multiple signatures were assessed for predictive accuracy and gene composition. The initial set of predictive genes is a subset of a larger group of 825 genes with predictive power. Many of the predictive genes are interchangeable because of a similar expression pattern across the tumor samples. The head and neck metastasis signature has a more stable gene composition than previous predictors. Exclusion of the strongest predictive genes could be compensated by raising the number of genes included in the signature. Multiple accurate predictive signatures can be designed using various subsets of predictive genes. The absence of genes with strong predictive power can be compensated by including more genes with lower predictive power. Lack of overlap between predictive signatures from different studies with the same goal may be explained by the fact that there are more predictive genes than required to design an accurate predictor.

Where to draw the mitral isthmus line in catheter ablation of atrial fibrillation: histological analysis.

AIMS: A linear lesion between the left inferior pulmonary vein orifice and mitral annulus, the so-called mitral isthmus, may improve the success of catheter ablation for atrial fibrillation. Gaps in the lesion line, however, may facilitate left atrial flutter. The aim of the study was to determine the optimal location of the lesion line by serial sectioning of the isthmus area. METHODS AND RESULTS: In a post-mortem study of 16 patients with normal left atria, serial sections of the isthmus area from 10 mm superior to and 30 mm inferior to the isthmus were studied by light microscopy. The length of the isthmus was 35+/-7 mm. On average, the muscle sleeve around the coronary sinus ended 10 mm inferior to the isthmus. The prevalence of a ramus circumflexus <5 mm from the endocardial surface, decreased from 60% in the most superior section to 0% in the most inferior section. Atrial arteries were frequently present in all sections. CONCLUSIONS: The thickness of atrial myocardium, the ramus circumflexus sometimes very close to the endocardium, a myocardial sleeve around the coronary sinus, and local cooling by atrial arteries and veins may complicate the creation of conduction block in the mitral isthmus.