[Protection of eye lens in computed tomography--dose evaluation on an anthropomorphic phantom using thermo-luminescent dosimeters and Monte-Carlo simulations]

PURPOSE

The lens of an eye is a particularly radiosensitive organ. This study investigates two different materials for eye shielding during CT scanning, i. e. a commercially available bismuth protector and a newly developed material for eye shielding, comprised of an alloy of Bi/Sb/Gd/W.

MATERIALS AND METHODS

The radiation dose during head CT scanning was measured using thermoluminescence dosimeters and an anthropomorphic Alderson-RANDO phantom. A radiation dose reduction was compared to two shielding materials and to the condition without any eye shielding. The effect of gantry angulation that excludes the eyes from beam path was also investigated. Radiation dose measurements were validated using a Monte-Carlo simulation. For this simulation we used the EGSsnr code system, and a new application CTDOSPP was developed for simulation of the computed tomography examination. Eight radiologists evaluated the diagnostic quality of the images.

RESULTS

Dose measurements and Monte-Carlo simulations are in good agreement. If the eye shields are placed in the primary beam path, bismuth eye shielding and the new material reduce the dose by up to 38 % and 48 %, respectively. Angling the gantry causes an 88 % reduction in radiation dose. All shielding materials generate beam hardening artifacts located close to the protector, but the artifacts do not spread into the brain.

CONCLUSION

The application of eye shields during CT examination of a head causes a significant reduction in radiation dose. The new protector material shows a significantly higher dose reduction in contrast to the commercially available bismuth shield. The best protection from radiation dose can be attained using gantry angulation.

Virtuelle Organisation im digitalen Zeitalter der Radiologie - Prinzip und Lösung für die radiologische Forschung?∗

The research project "VICORA - Virtual Institute for Computer-Assisted Radiology", funded by the German Federal Ministry of Education and Research, was initiated in the year 2000. Its virtual organization brings together physical science, engineering, information technology, clinical radiology and the medical technology industry. In the German radiology research domain VICORA serves as a model for interdisciplinary collaboration for the changing radiology paradigm illustrated by a "radiologycube". The project does not only aim at scientific goals but also considers the infrastructure, components and human resource management within a virtual organization. The common rapid prototyping platform ILAB 4 ensures user-friendly and time-efficient software that assists with the routine radiology work-flow including full DICOM functionality. By offering a new work environment and collaborative culture based on telematics and knowledge exchange in radiology research, VICORA overcomes limitations of traditional research organization.

[Bone adaptation changes mechanical stress in the femur--a prospective two years follow up after Hüft-TEP implantation]

AIM

Periprosthetic adaptive bone remodeling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodeling theory with finite element analysis. Unfortunately, there is still a lack of clinical validation data. The collection of prospective volumetric bone density data with a clinical computerized tomography study after THA was previously conducted. The objective of the study presented here is an additional evaluation of femoral strain.

METHOD

In a prospective clinical trial with 7 female patients after THA computerized tomography (CT) and finite element (FE) modeling was patient specifically combined immediately after surgery, as well as at three and 24 months postoperatively. Mechanical strain was expressed by strain energy density.

RESULTS

Corresponding to a bone density decrease, a decrease of the femoral strain energy density was observed during the two year follow-up after surgery (approximately 20 %). The predominant change occurred within the first three months and was found to be distally stronger than proximally.

CONCLUSION

As far as we are aware, this is the first combination of fully prospective 3D CT density data in vivo with patient-specific finite element modeling. The assessment of mechanical strain data during a follow-up trial should be a new approach for analyzing hip stems in clinical biomechanics. A future confirmative study based on a statistical case number calculation would increase the evidence of the results presented here.

[Selection of subjects: a problem of clinical trials in traumatology. Selection effects and the problem of representation as exemplified by a prospective randomized trial on whiplash injuries]

INTRODUCTION

The internal and external validity of studies is endangered by many factors, such as selection of subjects for inclusion. Selection bias itself is a major problem, but remains unmentioned and probably unexamined in the majority of published clinical trials in traumatology.

AIM OF THE STUDY

The aim of this investigation was to detect effects of subject selection which occurred during our own prospective intervention study. The clinical trial compared subjects with whiplash injury who were either treated by early mobilization or immobilization (soft collar).

MATERIAL AND METHODS

Source population, eligible subjects, study participants and final study participants were compared for differences on various items like age, gender and further sociodemographic as well as crash related factors and clinical findings.

RESULTS

Between 21.08.1997 and 30.04.1999 a total of 732 patients was examined and treated after whiplash in our trauma department. The options for inclusion were met by 453 patients. While 346 escaped from the study, 107 agreed to participate. Of these another 39 patients dropped out of the study. Selection effects were detected on two different levels, leading to distinct statistical procedures from those proposed in the study protocol.

CONCLUSIONS

Uncontrolled selection effects could undermine the interpretability of the results of clinical trials. Awareness of selection effects is mandatory regarding the applicability of these results to subjects, other than those in the group of the final study participants.

[Thromboembolism complication in multiple trauma patients: an underestimated problem? Results of a clinical observational study of 50 patients]

INTRODUCTION

The incidence of thromboembolic complications in patients with severe polytrauma in the ICU is not well known. Only a few publications deal with this problem. Systematic investigations in this high-risk patient group are not routinely used.

METHOD

From January 1996 to January 1998, 50 polytrauma patients with a mean ISS > 15 were included in a clinical study to evaluate the incidence of thromboembolism in this patient group. Further inclusion criteria were a minimum stay of 72 h in the ICU and mechanical ventilation for a minimum time of 72 h. All patients were examined with color-coded duplex sonography according to a standardized protocol. The duplex sonography was performed before the patients were first mobilized in the ICU (15 +/- 12.8 days).

RESULTS

If not otherwise indicated all values are given as mean +/- SD. The age of the patients was 38 years (range 17-77 years), the severity of trauma was characterized by an ISS of 40 (range 16-70). Eight of the included patients died during their stay in the ICU after developing a multiple organ failure. According to autopsy data none of them had a deep venous thrombosis or pulmonary embolus. Eight patients (19%) developed deep venous thrombosis, and 4 patients with thrombosis developed pulmonary embolism.

CONCLUSION

The incidence of deep venous thrombosis in polytrauma patients seems to be much higher than expected reviewing the results of other publications. The low detection rate of other authors results from using only clinical signs. The routine use of color-coded duplex sonography is effective in detecting unsuspected deep vein thrombosis.

[Effects of shaft length of finger joint prostheses on tension distribution in the bone]

In order to investigate the influence of stem length in finger joint prostheses on stress in the surrounding bone area, finite element (FEM) calculations of finger bones before and after prosthetic replacement of metacarpophalangeal joints with cementless implants of different stem length were performed. CT scans of the metacarpal bone and proximal phalanx before and after implantation of a prototype of a noncemented semiconstrained implant for the MP joint, which has been developed to replace metacarpophalangeal joints destroyed by rheumatoid arthritis, were analysed. The FEM calculations showed comparatively decreased differences of the von-Mises stress after implantation of intramedullary stems reaching the middle of the diaphysis. At the metaphysis of the metacarpal head we found an increase of the von-Mises stress of 1.3 MPa (Mega Pascal = 10(6) Pa), an increase of 18.9 MPa around the shortest prosthesis and a decrease of 21.4 MPa around the prosthesis with the longest stem.

Bone remodelling in humeral arthroplasty: follow-up using CT imaging and finite element modeling--an in vivo case study

Little material is available in the literature about remodelling of the human humerus after implantation of a shoulder hemiarthroplasty. A 73-year-old patient was examined by CT 4 years after implantation of a right shoulder hemiarthroplasty, and the bone density as represented by Hounsfield values was compared with the contralateral side. Additionally, a three-dimensional finite-element model was generated from the image data and analysed. Bone density was reduced around the prosthesis when compared with the contralateral side. The stresses were transmitted through the prosthesis, while low bone stresses were found surrounding the prosthesis. Distally from the prosthesis, high stresses were found. On the control side, a more homogeneous stress distribution was noted. The results could be explained by bone resorption around the prosthesis caused by stress shielding; this hypothesis has to be confirmed by future studies.

[Testing dental implants with an in vivo finite element model]

The finite element method (FEM) makes it possible to simulate biomechanical situations on a computer. In the present study the so-called voxel method [9, 14, 17, 18, 19] was used for the construction of the mandible model. For this, the relationship between the biological tissue (e.g. bone) and the corresponding attenuation coefficient of CT data (Hounsfield units = HU) were utilized. The CT data were obtained from an edentulous patient provided with a prosthesis borne on two titanium implants. In a parallel study, the bite forces of the same individual were measured. These were recorded digitally in three dimensions (cranio-caudal, anterior-posterior and left-right) The forces determined by a special program were then transferred to the FEM model implants. We were able to show that a bar joining the implants had a far greater effect on maximum equivalent stress than was expected from the measuring data alone. The highest stress at maximum occlusive force was lowered by 704% on using the connecting bar. On chewing, a stress reduction of 59.9% was observed. The reduction in stress achieved by the bar could, we believe, prolong the life of the implant.

[X-rays taken by radiologists! Influence on a continuous quality improvement process?]

PURPOSE

To evaluate how the training of radiology residents in taking radiographs influences the work of radiographers and the established quality standards.

METHODS

A first year radiology resident was trained for 4 weeks in focusing and exposure techniques by radiographers. In a second period the resident took 582 radiograms, which were compared with those taken by technicians for error estimation on a daily basis. During a third period the radiographs were produced in a contest between the resident and a skilled radiographer. Errors were analyzed by two independent experts according to established guidelines of the German Medical Association.

RESULTS

At the beginning of the second period the average error rate of the resident was 11.9% as compared to 8.9% in the technicians team, in the following month 9.2% versus 15.9%. In the third period no relevant difference in errors could be observed. Finally, unexpected quality improvements were implemented like an improved standardization of focusing and exposure techniques as well as dose reduction.

CONCLUSIONS

Radiology residents easily learn focusing and exposure techniques and achieve comparable results as radiographers within a short period of time. The additionally achieved knowledge improves the technical process of taking radiographs. We recommend to include a two plane radiography training period in the curriculum of radiology residents. It reinforces the radiologist's role in continuous quality improvements of the diagnostic process.

Comparison of geometry-based and CT voxel-based finite element modelling and experimental validation

The objectives of the paper presented here is the comparison of a geometry-based and voxel-based finite element (FE) method preprocessor of the human femur. The models were experimentally validated by strain gauge measurements (principal stress). The correlation coefficients (r) between the three methods (geometry-based FEM, voxel-based FEM, strain gauge measurements) were found to be in the range 0.91-0.94 (r2: 0.84-0.88). The relationships between the samples are highly significant (P = 0.001), where the strain gauge results are the independent variables. These results suggest that the validity with respect to the principal stress of a voxel-based modelling is similar to the validity of geometry-based modelling. In summary, therefore, we conclude that voxel-based meshing allows a straightforward interfacing with computerized tomography (CT) scans and might contribute to a clinically applicable FEM technology.

[Radiation exposure during thoracic radiography at the intensive care unit. Dose accumulation and risk of radiation-induced cancer in long-term therapy]

PURPOSE

Assessment of the additional morbidity risk due to repeated bedside chest radiography according to ICRP 60 during intensive care.

MATERIAL AND METHODS

Ventral surface doses were recorded by thermoluminescence dosimetry in 2 man and 7 women, mean age 36 +/- 12 years, mean height 169 +/- 5 cm, mean weight 74 +/- 8 kg, receiving long-term ventilation therapy due to Adult Respiratory Distress Syndrome (ARDS).

RESULTS

From 18 to 126 days duration of therapy 9 patients received a total of 348 bedside chest radiographs, mean 39 +/- 22 radiographs per patient. 217 chest radiographs yielded 217 surface doses and 217 gonadal doses. Patient's mean surface dose varies between at least 0.31 +/- 0.12 mGy and at most 0.56 +/- 0.09 mGy. The surface dose representing gonadal exposure is less than 0.03 mGy per exposure. The mean effective dose is about 0.15 mSv per exposure. The cumulative effective dose Heff ranges between 2.49 mSv and 14.09 mSv, thus estimating the additional individual cancer risk ranges between 0.01% and 0.07%.

CONCLUSION

In comparison with the decreased prognosis of severely ill long-term ventilated patients the additional morbidity risk due to chest radiographs is a negligible quantity.

[Standardized enteroclysis. Monitoring of intra-lumen pressure in 3 different patient groups]

PURPOSE

Monitoring of intraluminal pressure in standardized enteroclysis.

MATERIAL AND METHODS

Pressure monitoring with a double-lumen tube during fluoroscopy-guided adjustment of contrast media instillation rate due to small bowel motility and contrast media transport of 67 patients. Stratification according to patient data and findings in enteroclysis: Crohn's disease (n = 12), non-inflammatory disease (n = 35) and irritable bowel syndrome (n = 20).

RESULTS

The amount, instillation period and rate of contrast media and distension media were not statistically different within the study population. Crohn's disease patients showed elevated intraluminal pressure at the end of the distension phase (47.94 +/- 10.42 cm H2O versus 38.03 +/- 10.08 and 39.55 +/- 9.74 cm H2O, respectively, P = 0.0099), as well as at the end of the examination (48.59 +/- 10.42 cm H2O versus 39.66 +/- 6.52 and 35.67 +/- 8.28 cm H2O, P = 0.0002). In comparison with both other patient groups, maximum intraluminal pressure in Crohn's disease is higher and totals 51.75 +/- 9.94 cm H2O versus 43.00 +/- 6.20 and 39.55 +/- 9.74 cm H2O, P = 0.0010. Patients with Crohn's disease require a longer instillation period of distension media (28.05 +/- 12.82 min, not statistically significant).

CONCLUSION

Intraluminal pressure differs in standardized enteroclysis with fluoroscopy-guided instillation rate adjustment. Irrespective of stenosis or acute inflammation, patients with Crohn's disease show a higher intraluminal pressure compared to patients with non-inflammatory disease or irritable bowel syndrome.

[Fully automated generation of hip prosthesis voxel models of the femur for finite element analysis. Comparison of direct and subsequent prosthesis implantation]

Two means of generating implant-bearing FE voxel models of the human femur are described and compared. The first method consists in the fully automatic production of a femur model from CT data and subsequent implantation of a prosthesis stem on the basis of a redefinition of existing voxel elements using geometrical data control. The second method processes the CT data of a femur already bearing a prosthesis. Here, the prosthesis elements are generated separately from the surrounding bony elements on the basis of the differing CT density thresholds. Although the two implantation algorithms produce comparable results, they have different fields of application. The method of numerical stress analysis involving automatic generation of voxel models can be applied to implant-bearing femurs. Clinical follow-up observations of patients with prostheses made of titanium can be supported by FE calculations.

[Blunt thoracic trauma with aortic rupture and lung contusion caused by hoof kick in a 15-year-old girl. Diagnostic and therapeutic management]

The number of published cases of adolescents surviving thoracic aortic injuries with accompanying severe thoracic injuries is small. Only 20-30% of all these patients reach the trauma center alive. In the present case we demonstrate the diagnostic, operative and intensive care management in a 15-year-old girl. The exact interpretation of the AP thoracic X-ray in connection with a typical mechanism of injury led to the detection of a haemomediastinum. This is very important in the further development of diagnostics, because the conventional X-ray picture does not show significant signs in the case of an incomplete aortic rupture. Diagnostic hints have to be derived from the detection of the haemomediastinum. The girl was operated on under left heart bypass. Spinal ischaemia was absent after surgery, and renal failure also did not occur. The adjacent severe lung confusion healed under kinetic therapy with a kinetic treatment table without pulmonary complications.

Prospective evaluation of different diagnostic techniques for the detection of liver metastases at the time of primary resection of colorectal carcinoma

OBJECTIVE

To evaluate preoperative and operative methods of detecting liver metastases in patients undergoing primary resection for colorectal carcinoma.

DESIGN

Prospective, open study.

SETTING

Teaching hospital, Germany.

SUBJECTS

51 Patients with confirmed primary colorectal carcinoma.

INTERVENTIONS

Computed tomography during arterial portography (CT-AP), percutaneous ultrasonography (US), operative palpation and examination of the liver, operative US, and computed tomography (CT) follow-up 6-12 months postoperatively.

MAIN OUTCOME MEASURES

Sensitivity, specificity, positive and negative predictive value, and accuracy.

RESULTS

Overall accuracy was worst for CT during portography, because of the diagnosis of many false positive lesions. Exploration and palpation of the liver had the highest sensitivity (83%) and specificity (100%), and operative US did not give any useful additional information.

CONCLUSIONS

Preoperative percutaneous US is recommended as the best non-invasive screening test; otherwise careful inspection and palpation during operation are sufficient for the evaluation of the liver during primary resection for colorectal carcinoma.

[Windmill principle versus clockwork principle--tradition and interaction in academic lectures. A. N. S. A. Radiologica]

In reply to depersonalization of teaching, students hiding behind anonymity and their decreasing effective presence in campus life, academic teaching has to become practice-oriented, attractive and at least more effective. The traditional teacher-based lecture competes with student-centered and issue-related academic events like problem-based learning, thus, concerning student-teacher interaction. The model of a clockwork represents the components of a traditional lecture. The model of a windmill is suitable for explaining synergistic effects in scope and experience during an interaction concerned lecture. An example of student-teacher interaction and students' activation even in a preclinical course of lectures on anatomy and radiology is given. A high response and acceptance of the lecture is assured by structure-and process-oriented features.

[Status of radiation protection courses for physicians--plea for a change in paradigm]

The purpose of this study was to evaluate the acceptance of the statutory course of radiation protection, which is attended by physicians. As a first step towards problem based quality management, an anonymous questionnaire was used to assess the participants' opinions. The present methods in teaching, practice-orientation of the educational objectives, the prize and efficiency of the course were judged poor. Neither valid indicators of quality nor a quality management of the course exists. Facing the status quo and future demands within the medical community and society there is a serious need for reshaping radiology. It is emphasized that instead of marginal corrections only a strategic and fundamental approach to a paradigmatic reorganization will meet success.

[3-D imaging of the liver]

Three dimensional imaging of the liver is focused on the spatial visualization of focal lesions in relation to vascular landmarks to support surgical decision making. Additionally the volume estimation of metastases or liver segments is considered in the patient's oncologic follow-up and the planning of the surgical approach. Spiral-CT is destined for 3D imaging, as it represents a standardized, minor invasive, time and cost saving method. Current developments of 3D sonography of the liver are reported. While a special application of 3D imaging, i.e. CT angiography (CTA), replaces preoperative arterial angiography in liver transplantation candidates the diagnostic gold standard for lesion detection still remains by reason of missing algorithms the interpretation of a 2D data set. Validation of 3D versus 2D imaging of the liver demands controlled trials to evaluate the diagnostic potential, time and cost savings of dedicated acquisition techniques, postprocessing algorithms and display modalities.

[Color-coded duplex ultrasound and laser Doppler flowmetry of finger tips of healthy probands]

In the study presented, color-coded duplex sonography (CCDS) and laser Doppler flux (LDF) signals from finger tips of 7 healthy individuals were recorded simultaneously. The aim of the study was to examine whether or not the results of a functional test ('deep inspiration') could also be observed with an ultrasonic Doppler. In the literature this test is known to provoke notable blood flow characteristics of the LDF ('inspiratory gasp'), a phenomenon which is caused by a sympathetically mediated vasoconstriction of acral vessels. With regard to the penetration depth of the LDF in skin it was of further interest to determine the distance between the surface of the skin and the vessels found near the surface. We found for CCDS parameters (color pixels/image; time-averaged flow velocity [TAV]; resistance index [RI]) as well as for LDF (flux [taLDF]) significant changes before versus after 'deep inspiration'. CCDS is a new diagnostic tool to visualize also very small vessels down to 0.2 mm, e.g. in finger tips. It should be evaluated which role this method may play in combination with functional tests in diagnostic handling, e.g. of patients with polyneuropathies or collagenoses.

[Use of voxel-oriented femur models for stress analysis. Generation, calculation and validation of CT-based FEM models]

A means of interfacing computed tomography with the finite element method for the analysis of stress distribution in human femurs is described. With the aid of data transfer and image processing programs, three-dimensional voxel models of four macerated and a fresh-frozen cadaveric femur were generated from CT data sets. The underlying basic principle is direct generation of model elements from one or more adjacent CT-voxels, which are characterised by their coordinates and local absorption coefficients. A new algorithm was used for smoothing the edges of the model. All the models were analysed with respect to their stress distribution under different load situations, and the results were compared with the data of a parallel study utilizing the strain-gauge technique. Using the method of linear regression, a high correlation (coefficient of determination r2: 0.80-0.91) was found between the calculated and experimentally measured principal stresses at the surface of the bones.

[Hypertrophic osteoarthropathy as indicator for bronchial carcinoma]

Clubbing of the fingers and periosteal bone formation are the typical signs of hypertrophic osteoarthropathy, which mostly is a secondary manifestation of an underlying disease. Reporting a case of hypertrophic osteoarthropathy in association with bronchial carcinoma, we stress the importance of an extensive diagnostic evaluation with chest X-ray as a first step.

Portal vein reconstruction based on topology

Traditionally the intrahepatic vascular anatomy is correlated to the segment anatomy of the liver for which--following Couinaud [1]-the portal vein has been accepted as a guiding structure. This paper proposes a new method for the extraction and 3D-visualization of the portal vein based on Spiral CT data. Starting from a seed voxel, the algorithm expands stepwise within the structure of interest. Bifurcations are recognized and a symbolic tree is generated simultaneously which allows for interactive identification of sub-branches, their selection and specific colouring. The method is able to extract at least three generations of branches of the portal vein. A volume renderer is used to visualize the reconstructed portal vein superimposed to a transparent view of liver tissue and focal lesions. This provides a new tool for the planning of segment-oriented liver surgery (e.g. localization of lesions relative to the portal vein). But the method promises also to be useful for other applications, e.g. comparative studies of liver anatomy and pathology, or portosystemic shunt operations--TIPS (transjugular intrahepatic portosystemic shunts).

Isolated clinical syndrome of primary aldosteronism in a patient with adrenocortical carcinoma. Case report and review of the literature

Primary carcinoma of the adrenal cortex is an extremely rare neoplasm, accounting for an estimated 0.05-0.2% of all malignancies. Hormonally functioning tumors occur in about 50% of patients with Cushing's syndrome (50%), virilism (30%) and feminization (12%) being the most common clinical manifestations. Isolated aldosteronism caused by adrenocortical carcinoma is found in about 1-3% in patients with the clinical signs of Conn's syndrome. The only preoperative feature suggesting malignancy is a size of more than 5 cm in computed tomography. We report a rare case of a 29-year-old man with biochemically proven primary aldosteronism as the unique manifestation of a carcinoma of the right adrenal cortex.

[Iodine-induced hyperthyroidism in metastatic thyroid carcinoma]

A 75-year-old man with nodular goitre (for the preceding 2 years treated with 75 micrograms/dl L-thyroxine) complained of pain over the left hip: on auscultation an arterial flow murmur was audible over the hip. The radiograph demonstrated extensive osteolysis in the flat part of the ilium. Search for the primary tumour, including two pelvic angiographs, was unsuccessful. Examination of a biopsy from the right ilium revealed a metastasis from a highly differentiated follicular thyroid carcinoma, which could not be demonstrated scintigraphically because of a reduced 99mTc-pertechnetate and 123I-iodine uptake, the result of the L-thyroxine administration. A thyrotoxic crisis occurred 2 days after the second angiography (free thyroxine 3.17 ng/dl, triiodothyronine 219 ng/dl, thyroglobulin > 250 ng/ml). Treatment with thiamazole (40 mg/d) and perchlorate (1 g/d) reduced the concentration of peripheral thyroid hormone, but the patient's general condition improved only slowly. As a result, radioiodine treatment could not be started until 9 months later. He died a further 9 months later from septicaemia originating from the metastasis.

[Is prevention of thromboembolism in ambulatory and conservative therapy of rupture of the fibular ligament of the upper ankle joint necessary?]

In a prospective clinical study, 111 outpatients with tears of the lateral ankle ligaments were investigated for the occurrence of deep venous thrombosis (DVT). All patients had been treated by a plaster cast for 1 week and had not received any form of DVT prophylaxis. After removal of the plaster cast (mean 7.1 days), colour flow imaging of the veins of the injured leg was performed. A phlebography was undertaken whenever there was any suspicion of DVT. Risk factors for thrombosis [3, 10] were documented in all patients. Besides injury and immobilisation, a median of 1.2 (0-4) risk factors for DVT was involved. Only 31 patients had no additional risk factors at all. Median age of the patients was 26.1 years (16-53 median range). Only 1 patient over 40 years of age was diagnosed as having DVT, and none under 40. Therefore, medicamentous prophylaxis of DVT is not considered necessary in outpatients younger than 40 years with ankle ligament tears treated by bi-valved casts in cases when there are no additional risk factors (Table 4) for DVT.

[Biventricular inflow tract compression by chronic organized hemopericardium in Caplan syndrome]

We report the case of a 59-year old patient with the rare combination of silicosis and rheumatoid arthritis, which is called Caplan's syndrome. The patient presented with right heart failure caused by a pericardial tumor compressing the right and the left ventricle. By means of several imaging techniques it was possible to elucidate the topographic relations of the tumor. Definite signs of malignant growth were not found. Despite his elevated perioperative risk we decided to operate on the patient. During the operation macroscopic and histologic evidence revealed that the tumor was not a neoplastic process but consisted of an organized hemopericardium. This demonstrates that pericarditis in rheumatoid arthritis can be hemorrhagic and can mimick a malignant pericardial tumor. The decision to operate was first supported by the findings of the applied imaging techniques, the normal endomyocardial biopsy, and the clinical course and were later confirmed in situ.

[Clavicular fractures after radical neck dissection]

Fracture of the medial end of the clavicle as a late complication following radical neck dissection is rare, with an incidence of approximately 0.4%-0.5%. Radical neck dissection alters the mechanics of the shoulder girdle, and distorts normal muscle forces acting on the clavicle. We present two patients to illustrate the problems of differential diagnosis and mechanism of fracture. Once the diagnosis has been made the fracture should be managed conservatively, although clinical and radiological differentiation from avascular necrosis or bony metastasis may be difficult. Biopsy is essential in doubtful cases.