Nonlinear elasticity and short-range mechanical coupling govern the rate and symmetry of mouth opening in Hydra.

Hydra has a tubular bilayered epithelial body column with a dome-shaped head on one end and a foot on the other. Hydra lacks a permanent mouth: its head epithelium is sealed. Upon neuronal activation, a mouth opens at the apex of the head which can exceed the body column diameter in seconds, allowing Hydra to ingest prey larger than itself. While the kinematics of mouth opening are well characterized, the underlying mechanism is unknown. We show that Hydra mouth opening is generated by independent local contractions that require tissue-level coordination. We model the head epithelium as an active viscoelastic nonlinear spring network. The model reproduces the size, timescale and symmetry of mouth opening. It shows that radial contractions, travelling inwards from the outer boundary of the head, pull the mouth open. Nonlinear elasticity makes mouth opening larger and faster, contrary to expectations. The model correctly predicts changes in mouth shape in response to external forces. By generating innervated : nerve-free chimera in experiments and simulations, we show that nearest-neighbour mechanical signalling suffices to coordinate mouth opening. Hydra mouth opening shows that in the absence of long-range chemical or neuronal signals, short-range mechanical coupling is sufficient to produce long-range order in tissue deformations.

Retained Ureteral Stent Encrustation After Stent Removal: A Case Report.

Ureteral stents are used to relieve acute or chronic urinary tract obstructions and may be complicated by stent encrustation. The development of encrustation is related to indwelling time, stent composition, bacterial biofilm formation, malabsorptive disorders, metabolic disorders (hypercalcemia, hyperuricosuria, pH imbalance), and cancer. Without intervention, encrustation may lead to luminal obstruction, infection, stent fracture, or ureteral avulsion during removal. Rarely, forced removal of an encrusted stent may cause the encrustation to remain in the urinary tract which can lead to further complications. Diagnosis of a retained encrustation includes evaluation with X-ray, ultrasound, and CT. Management strategies of retained encrustations are not standardized but may include removal with flexible ureteroscopy. In the following case, we present a 58-year-old male with retained encrustation material following non-forced stent removal that was not readily observed on initial imaging. CT demonstrated a curved, tubular radiodensity representing calcified encrustation material, and the diagnosis of retained encrustation was confirmed after successful removal with flexible ureteroscopy. We concluded that ureteral stent encrustation can remain in the urinary collecting system following stent removal, although this complication is rare and not well studied.

["Halle surgery week": how a teaching format awakens medical students' interest in surgery]. / "Hallesche OP-Wochen": Wie ein Lehrformat das Interesse von Medizinstudierenden an der Chirurgie weckt.

BACKGROUND: A practical education in surgery is difficult to conduct in a student-centered manner and is thus often inadequate. New teaching concepts are required to provide students with insights into surgery and make the field more appealing. METHODS: As part of a two-week facultative event, medical students followed eight live surgical procedures from different disciplines from an auditorium. In the auditorium, the procedures were simultaneously moderated by an experienced surgeon. Before and after every procedure, questionnaires were used to analyze whether the teaching event was suited to improve an understanding and interest for the field of surgery. RESULTS: A total of 709 completed questionnaires (pre and post) from 381 students were collected. The self-reported learning effect was evaluated as good or very good by students. In many of the presented disciplines, experiencing a live surgical procedure was associated with significant positive changes in attitude regarding each discipline in general, a potential clinical traineeship in the discipline and choosing the discipline as a later specialization. CONCLUSION: The high attendance as well as the evaluation results suggest a high acceptance for the teaching event. The teaching format is suited to improve the understanding of surgical procedures and had a positive effect on medical students' attitude towards surgical disciplines.

Mediastinal ganglioneuroma with osseous invasion simulating malignant transformation of osteochondroma on CT imaging.

Ganglioneuromas (GN) are rare, mature tumors that arise in the posterior mediastinum or retroperitoneum from neural crest cells and present as slow growing masses in the pediatric population. While they are often found incidentally in unrelated diagnostic workup, they can become symptomatic due to their size and location. They typically demonstrate the nonspecific appearance of a solid mass without invasive or destructive features across different modalities. Such features are normally indicative of more aggressive neoplasms from similar cellular ancestry or an entirely different lineage. Here we present a case of mediastinal GN that on imaging was initially suggestive of an osteochondroma with malignant degeneration based on the presence of an exostosis associated with a large solid mass. Final pathology, however, revealed GN with involvement of the adjacent bone. While the final diagnosis was benign, it is important to recognize this pattern of exostosis with solid mass, especially since the overall survival rate of sarcomata is much worse than that of a classic GN.

Radioprotective agents to prevent cellular damage due to ionizing radiation.

Medical imaging has become a central component of patient care to ensure early and accurate diagnosis. Unfortunately, many imaging modalities use ionizing radiation to generate images. Ionizing radiation even in low doses can cause direct DNA damage and generate reactive oxygen species and free radicals, leading to DNA, protein, and lipid membrane damage. This cell damage can lead to apoptosis, necrosis, teratogenesis, or carcinogenesis. As many as 2% of cancers (and an associated 15,000 deaths annually) can be linked to computed tomography exposure alone. Radioprotective agents have been investigated using various models including cells, animals, and recently humans. The data suggest that radioprotective agents working through a variety of mechanisms have the potential to decrease free radical damage produced by ionizing radiation. Radioprotective agents may be useful as an adjunct to medical imaging to reduced patient morbidity and mortality due to ionizing radiation exposure. Some radioprotective agents can be found in high quantities in antioxidant rich foods, suggesting that a specific diet recommendation could be beneficial in radioprotection.

Treatment of metastatic sarcoma to the liver with bland embolization.

BACKGROUND: The authors evaluated the impact of bland particle embolization on survival in patients with metastatic sarcoma to the liver. METHODS: Twenty-four patients with liver-dominant metastases from sarcoma were treated with particle embolization from 1996 to 2002. Primary tumors included 16 gastrointestinal stromal tumors (GISTs), 7 intestinal leiomyosarcomas, and 1 liposarcoma. Thirteen patients had known extrahepatic disease. Embolization was performed by using polyvinyl alcohol or trisacryl microspheres to effect stasis in the target vessel(s). Follow-up images to assess response were obtained 4 weeks after the procedure. Decrease in the size of the target lesion by >25% or development of >50% necrosis on follow-up imaging was considered a treatment response. RESULTS: Nineteen patients had metachronous liver metastases, and the median disease-free interval was 22 months (range 10-156 months) from resection of the primary tumor. Ten patients underwent prior liver resection for metastatic disease. Of 15 evaluable patients, 9 patients (60%) had a radiographic response. The median follow-up for all patients was 21 months. The median follow-up for surviving patients was 59 months. Overall survival from the time of initial embolization was 62% at 1 year, 41% at 2 years, and 29% at 3 years. Patients who had radiographic evidence of response survived significantly longer than patients who did not respond (63 months vs. 19 months; P < .007). Patients with GIST survived significantly longer than patients with visceral leiomyosarcoma (median, 36 months vs. 18 months; P < .03). CONCLUSIONS: Bland embolization was efficacious in some patients with metastatic sarcoma to the liver. Radiographic evidence of response was correlated with improved survival. This regional therapy may enter the treatment algorithm for patients who have unresectable disease or disease that has failed conventional therapies.

Arterial embolization for salvage of hepatic artery infusion pumps.

PURPOSE: Hepatic artery infusion pumps (HAIPs) ideally provide for homogenous perfusion of the liver with chemotherapeutic agents. Perfusion of extrahepatic organs or asymmetric liver perfusion (ie, "misperfusion") is diagnosed by nuclear scintigraphy and precludes the use of HAIPs. The purpose of this study is to report experience in salvaging HAIPs with arterial embolization. MATERIALS AND METHODS: A single-center HAIP database was retrospectively reviewed for cases from 1999 to 2005 to identify patients who underwent angiography to treat misperfusion documented by nuclear scintigraphy. Patient demographics, nuclear scintigraphic findings before and after embolization, angiographic findings, embolization variables, and outcomes were recorded. Technical success (defined by cessation of flow to the vessel responsible for misperfusion) and clinical success (ie, successful use of the pump) were calculated. RESULTS: During the study period, 475 HAIPs were implanted. Of those, 43 (9%) had abnormal nuclear scintigraphic findings of misperfusion, but only 32 (7%) had angiographic abnormalities. In eight of 32 cases, hepatic arterial thrombosis and extravasation at the catheter tip were found, which precluded salvage by embolization. In 24 of 32 cases, a vessel presumed responsible for the misperfusion was identified and targeted for embolization. Technical success and clinical success were achieved in 21 of 24 patients (87.5%) and 19 of 24 patients (79%), respectively, who underwent 27 embolization procedures. The three technical failures (12.5%) were the result of inability to catheterize the identified vessel. CONCLUSIONS: Percutaneous arterial embolization of a vessel to correct misperfusion shown by nuclear scintigraphy is safe and effective. This approach can be expected to result in HAIP salvage in the majority of patients.

Particle embolization of recurrent hepatocellular carcinoma after hepatectomy.

BACKGROUND: Complete surgical resection is the mainstay of treatment for patients with hepatocellular carcinoma (HCC). Unfortunately, most patients ultimately develop disease recurrence and the median survival from the time of recurrence is <1 year. The purpose of the current study was to review the authors' experience using bland hepatic arterial embolization to treat recurrent HCC after definitive surgical resection. METHODS: The authors reviewed their single-center hepatic embolization database from 1995 through 2004 to identify patients who underwent bland hepatic arterial embolization for disease recurrence. Data analyzed included patient demographics, Okuda stage and Child score, imaging findings, and embolization variables. Recurrence-free survival (from surgery to disease recurrence) and survival time (from recurrence to last follow-up) were calculated using the Kaplan-Meier method. RESULTS: The authors identified 45 patients treated with bland embolization for recurrent HCC after resection. Six patients also underwent ablative therapy after embolization. Of the 45 patients, 42 (93.3%) patients had Okuda Stage 1 disease. The median time to recurrence was 13 months. The median survival after embolization was 46 months, and actuarial survival rates at 1 year, 2 years, and 5 years after recurrence were 86%, 74%, and 47%, respectively, with a median follow-up of 31 months. Patients who developed disease recurrence with a solitary lesion had a significantly improved survival (P = .03) At the time of last follow-up, 3 patients (6.6%) were alive with no evidence of viable disease. CONCLUSIONS: Bland arterial embolization was found to be an effective method of salvage therapy for patients with good liver function with recurrent HCC after prior surgical resection. Patients whose disease recurred with a solitary lesion appear to have a significantly increased survival compared with patients who develop disease recurrence with multiple tumors. A small proportion of patients can be rendered without evidence of viable disease.

Safety and efficacy of preoperative portal vein embolization with polyvinyl alcohol in 58 patients with liver metastases.

OBJECTIVE: The objective of our study was to evaluate the safety and efficacy of transhepatic lobar portal vein embolization (PVE) using polyvinyl alcohol (PVA) particles to induce contralateral lobar hypertrophy in patients with liver-only metastases and normal underlying liver function. MATERIALS AND METHODS: Fifty-eight consecutive patients with small predicted future liver remnants (FLRs) underwent PVE with PVA particles to induce hypertrophy of the contralateral hemi-liver before surgical resection of liver metastases. Total liver, right hemi-liver, and left hemi-liver volumes were calculated before and after embolization using a 3D workstation. RESULTS: Eight patients underwent left PVE; 47, right PVE; and three, right and segment IV PVE. There were no major complications of the procedure. The mean increases in the ratio of the FLR to the total estimated liver volume after right, right and segment IV, and left PVE were 9%, 10%, and 3%, respectively; the corresponding mean hypertrophy ratios were 24.3%, 31.9%, and 1.5%, respectively. CONCLUSION: Right PVE using PVA particles alone as the embolic agent is safe and effective in achieving left hemi-liver hypertrophy. In contrast, left PVE did not induce significant right hemi-liver hypertrophy in this patient population.

Embolization of isolated lumbar artery injuries in trauma patients.

PURPOSE: The purpose of the study was to evaluate the angiographic findings and results of embolotherapy in the management of lumbar artery trauma. METHODS: All patients with lumbar artery injury who underwent angiography and percutaneous embolization in a state trauma center within a 10-year period were retrospectively reviewed. Radiological information and procedural reports were reviewed to assess immediate angiographic findings and embolization results. Long-term clinical outcome was obtained by communication with the trauma physicians as well as with chart review. RESULTS: In a 10-year period, 255 trauma patients underwent abdominal aortography. Eleven of these patients (three women and eight men) suffered a lumbar artery injury. Angiography demonstrated active extravasation (in nine) and/or pseudoaneurysm (in four). Successful selective embolization of abnormal vessel(s) was performed in all patients. Coils were used in six patients, particles in one and gelfoam in five patients. Complications included one retroperitoneal abscess, which was treated successfully. One patient returned for embolization of an adjacent lumbar artery due to late pseudoaneurysm formation. CONCLUSIONS: In hemodynamically stable patients, selective embolization is a safe and effective method for immediate control of active extravasation, as well as to prevent future hemorrhage from an injured lumbar artery.

CT-guided transvenous or transcaval needle biopsy of pancreatic and peripancreatic lesions.

PURPOSE: To evaluate the safety and efficacy of direct computed tomography (CT)-guided fine needle aspiration biopsy (FNAB) of pancreatic and peripancreatic masses via a posterior approach that traverses the inferior vena cava (IVC) or renal vein. MATERIALS AND METHODS: From January 2000 to July 2003, 55 patients underwent 58 biopsies of masses located within the pancreas (n = 28) or in a peripancreatic location (n = 30) with use of a posterior approach that crossed the IVC or renal vein. Biopsies were performed with needles ranging in size from 18 to 22. Cytology reports and medical records of all patients were retrospectively reviewed to evaluate diagnostic accuracy and complication rates. RESULTS: Masses were safely accessed with a direct (noncoaxial) pathway traversing the IVC (n = 54), renal vein (n = 4), or both (n = 3). Overall diagnostic accuracy was 86% (50 of 58). Cytologic examination was positive for malignancy in 39 of 58 biopsies (67%). Benign lesions were demonstrated in 12 of 58 biopsies. In seven cases (12%), the sample was deemed nondiagnostic. Of those, four were diagnosed later by endoscopy (n = 1), surgical biopsy (n = 2), or repeat FNAB (n = 1). A false-negative result was noted in one case, which was later diagnosed by repeat biopsy. A total of four inadvertent passes through the right renal artery were recorded. CT evidence of perilesional blood was seen in eight of 55 patients (eight of 58 cases). Three of these occurred after a passage via the right renal artery. All patients remained asymptomatic, and no transfusion or change in management was necessary. No other complications occurred. CONCLUSION: CT-guided noncoaxial FNAB with an approach that traverses the IVC or renal vein is safe and effective in obtaining diagnostic specimens from pancreatic and peripancreatic masses.

Displacement of endoscopically placed plastic biliary endoprostheses into the duodenum with a simple transhepatic technique.

The authors to describe the technique and report the results of percutaneous displacement of endoscopically placed plastic biliary endoprostheses into the duodenum at the time of transhepatic intervention in 34 patients. Displacement into the duodenum was effected by simply passing a guide wire through the stent, and then pushing it into the gut with a catheter. Thirty-three of 36 stents (92%) were successfully displaced in this manner. No complications related to stent passage out of the gastrointestinal tract were encountered. Plastic biliary stents can be safely displaced into the duodenum when patients undergo transhepatic biliary procedures, thus avoiding repeated endoscopy.