Application of HACCP principles to control visitor health threats on dairy farms open to the general public

An increasing number of Dutch dairy farmers have diversified their activities, often opening their farm up to visitors (tourist accommodation, farm shop, contact with livestock, etc). It is essential to prevent these visitors from having accidents or becoming ill, which could result in financial claims and might harm the reputation of the agricultural sector. This article describes how the hazard analysis critical control points concept and principles (HACCP) can be applied to these activities and integrated with on-farm operational herd health and production management programmes.

Effects of autologous stem cells on immunohistochemical patterns and gene expression of metalloproteinases and their tissue inhibitors in doxorubicin cardiomyopathy in a rabbit model

This study aims to investigate the expression of metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in chronic doxorubicin cardiomyopathy in a rabbit model and to evaluate the effects of bone marrow-derived mesenchymal stem cell (MSC) transplantation in this disease. Thirty-nine 3-month-old New Zealand rabbits were divided into 4 groups: group 1 (n = 9) was the untreated control. Groups 2-4 were treated with 6 weeks of doxorubicin (3 mg/kg). Group 2 (n = 6) received no further treatment. In group 3 (n = 9), animals were treated with culture medium (CM) alone. In group 4 (n = 15), autologous MSCs (1.5-2.0 x 10(6)/ml) were injected in the left ventricular (LV) wall. Hearts were stained with HE and picrosirius red. MMP-1, -2, -3 and -9 and TIMP-2 and -3 were detected immunohistochemically. The mRNA levels were determined by real-time polymerase chain reaction. The results confirmed that doxorubicin treatment resulted in minimal myocardial fibrosis and showed that expression of MMPs increased and TIMP-3 decreased. The injection procedure resulted in increased myocardial fibrosis in groups 3 and 4. After MSC injection, MMP-1, MMP-2, and TIMP-3 expression was higher than that in group 2. CM injection led to more fibrosis, elevated TIMP-3, but diminished MMP-1 and MMP-2 expression compared with MSC injection. The mRNA levels of MMPs and TIMPs were not significantly different among all groups. In conclusion, chronic doxorubicin cardiomyopathy was characterized by increased MMP and decreased TIMP-3 expression. MSCs injection into the LV resulted in marked differences of collagen content and MMP/TIMP expression in the whole heart, although significant numbers of living MSCs were not detected after 4 weeks.

Tumour budding as prognostic factor in stage I/II colorectal carcinoma

AIMS

The term tumour 'budding' has been coined for the detachment of tumour cells from the neoplastic glands of adenocarcinomas and is presumed to be an early step in the metastatic process. A limited number of studies have shown budding to be an adverse prognostic factor.

METHODS AND RESULTS

All primary single, non-metachronous TNM stage I/II colorectal carcinomas without neoadjuvant treatment resected in the years 1994-1999 were included (n = 186). Tumour buds were counted in pan-cytokeratin immunostains in a 0.785-mm2 field of vision (250 x). During follow-up 21 patients had distant metastases and 12 patients died of their disease. Budding was determined at 14 and 20.46, median and mean, respectively (range 0-120). A cut-off of 25 was found to be sensitive (0.76) and specific (0.739). Kaplan-Meier survival analysis showed high budding to be a strong adverse prognosticator. By Cox regression, high budding together with venous angioinvasion were independent prognostic factors.

CONCLUSIONS

This study confirms the prognostic value of budding in a contemporary series of colorectal carcinomas that by TNM were low risk. Technically easy, rapid and robust to determine, budding quantified in pan-cytokeratin stains significantly aids in the identification of high-risk patients and is recommended for more general use in surgical pathology.

Foreign body in the airway: unusual cause of acute dyspnoe after cardiac surgery

We report on a 68-year-old male who presented with acute onset of dyspnoea and cough. After coronary artery bypass grafting and mitral valve repair with an annuloplasty ring, postoperative recovery was initially uneventful. On the 6th postoperative day, he came back to intensive care unit due to acute dyspnoea. Fig. 1 demonstrates chest x-ray. We identified the foreign body as a dental prosthesis (Fig. 2). Removal from the right bronchial tree was successful using a flexible bronchoscope under local anesthesia; intubation was not required. This procedure was safe and well tolerated by the patient. Clinical presentation of adult foreign body aspiration are often nonspecific. Chest x-ray is very helpful for identification and localization of foreign bodies in the airway. Extraction can be performed with flexible or rigid bronchoscopy. For the removal, biopsy forceps, Fogarty balloon catheter, alligator forceps or wire baskets are effective.

Malignant conversion of florid oral and labial papillomatosis during topical immunotherapy with imiquimod

We report a case of a 61-year-old woman suffering from florid oral papillomatosis with a squamous-cell cancer of the floor of the mouth, which was removed by scalpel surgery combined with a radical neck dissection in 1996. Between 1996 and 2000 several histologically benign papillomatous lesions of mouth and lips were removed with laser and electrosurgery. However, the lesions recurred. In July 2000 hyperkeratotic, wart-like lesions were present at the lower and upper lips and at the right angle of the mouth and the adjacent oral mucosa. Overnight treatment with a topical 5% imiquimod cream on a Monday-Wednesday-Friday schedule was initiated. However, due to severe irritation and pain the application had to be reduced to 4 h per night, three times a week, followed by a therapy-free interval of 2 weeks. Despite this treatment consisting of four cycles of 3 weeks (1 week treatment and 2 weeks pause), the lesions increased markedly in size. A biopsy taken from the tumorous lesion from the right angle of the mouth proved to be a squamous-cell carcinoma. The tumors of the labial and oral mucosal sites as well as the right submandibular lymph nodes were removed by wide scalpel excision. The lips were reconstructed by plastic surgery. 24 months after surgical intervention no recurrence nor metastasis to lymph nodes or distal sites were observed.

Microvessel densities and microvascular architecture in colorectal carcinomas and their liver metastases: significant correlation of high microvessel densities with better survival

AIMS

Microvessel densities in cancers have been shown to be a prognostic factor for some types of cancer. For colorectal cancer, however, the situation is far from clear.

METHODS

A consecutive series of 173 colorectal carcinomas was investigated, and to these were added 55 liver metastases originating from colorectal cancer. Microvessels were counted in hotspots (factor VIII immunostaining, 0.74 mm2). The capillary architecture was scored according to the degree of order and envelopment of the neoplastic glands. Endothelial proliferation was determined by factor VIII/Ki67 double labelling.

RESULTS

Mean microvessel densities were 51.8 for colorectal carcinomas (range 8-140) and 31.9 for liver metastases (range 3-101). Stratification according to stage, depth of infiltration and nodal involvement showed a significant inverse relation with increase. Mean microvessel densities in primaries were significantly higher than in metastases. Kaplan-Meier analysis showed a significantly higher cancer-specific survival for high microvessel densities (median as cut-off) and for a more ordered microvascular architecture. Endothelial proliferation in carcinomas was significantly higher than in normal mucosa.

CONCLUSIONS

Contrary to other types of cancer, for colorectal cancer high microvessel densities confer good rather than poor prognosis. We hypothesize that neoangiogenesis, though extant in colorectal cancer, is not rate-limiting in the metastatic cascade.

[Choledochal cysts in adult patients--presentation and clinical course]

HISTORY

A 35-year-old male was admitted with recurrent acute pancreatitis of unknown origin. He was found to have a cystic lesion in the upper abdomen believed to be a pancreatic pseudocyst (patient 1). A 59-year-old female with a choledochal cyst developed acute pancreatitis (patient 2). A 32-year-old male who had been operated upon for a choledochal cyst during childhood was admitted for upper abdominal pain, fever and vomitus (patient 3).

INVESTIGATIONS AND DIAGNOSIS

Patient 1 was found to have a choledochal cyst type IV a according to TODANI. Patient 2 was diagnosed to have a choledochal cyst type Ib according to TODANI. The cyst was believed to contain a bile duct carcinoma. In patient 3, sonography showed an advanced Klatskin tumour with infiltration of the portal vein, the hepatic artery and the liver. Bile cytology confirmed the carcinoma. In all patients cholestasis was found. Pancreatic enzymes were elevated in patients 2 and 3.

TREATMENT AND COURSE

Patient 1 underwent left hemihepatectomy and received a biliodigestive anastomosis. In patient 2 the choledochal cyst was resected while undergoing pylorus-preserving resection of the pancreatic head. The tumour suspected was confirmed and R0 resected. Patient 3 presented with an incurable bile duct carcinoma. He died 3 months later from multiple lung emboli.

CONCLUSION

Choledochal cysts are associated with a 20 fold increase in the incidence of bile duct carcinoma.

p53 and K-ras mutations in pancreatic juice samples from patients with chronic pancreatitis

BACKGROUND

Mutations in p53 and ras genes are frequent in pancreatic carcinoma. Several ras mutations are consistently detected in the pancreatic juice from patients with chronic pancreatitis. The p53 gene mutations have been detected occasionally in chronic pancreatitis tissue. It was the aim of this study to evaluate the presence and clinical significance of p53 and ras mutations in clinical pancreatic juice samples from patients with chronic pancreatitis.

METHODS

Pancreatic juice was obtained from 66 patients with chronic pancreatitis and no evidence of pancreatic carcinoma (51 men, 15 women; age 17-86 years [mean 49.6 +/- 12.9]). Patients were followed prospectively for 26 +/- 3 (4-54) months. Detection of p53 gene mutations was by temperature gradient gel electrophoresis (TGGE) and single strand conformation polymorphism (SSCP) for exons 5-8. Analysis of ras mutations was performed by SSCP/polymerase chain reaction, restriction fragment length polymorphism/polymerase chain reaction. All mutations were confirmed by sequencing.

RESULTS

Five of 66 (7.5%) pancreatic juice samples contained p53 mutations, and ras mutations were detected in 6 cases (9%). Cytology was negative in all cases. No pancreatic carcinoma developed during follow-up and neither cancer cells nor preneoplastic lesions could be detected histologically in resected specimens. Although no correlation between p53 mutations and duration of pancreatitis or drinking habits was found, K-ras mutations correlated with both heavy smoking and severity of the disease.

CONCLUSION

p53 and ras mutations can be detected in a minority of pancreatic juice samples from patients with chronic pancreatitis in the absence of malignancy.

Low frequency of p53 and ras mutations in bile of patients with hepato-biliary disease: a prospective study in more than 100 patients

The diagnosis of biliary disease, namely malignant disorders, is frequently hampered by the inconclusive cytology. We investigated prospectively the frequency of molecular changes in p53 and ras compared with cytology in patients with primary or secondary hepato-biliary disease. We investigated 118 consecutive patients, aged 24-89 with the following clinical diagnoses: choledocho/cholecystolithiasis (28), cholangiocellular carcinoma (21), gall bladder tumor (8), liver metastasis (3), autoimmune disease (8), chronic pancreatitis (16), pancreatic carcinoma (11), papillary disease (4), hepatic cirrhosis (6), cholangitis (2), anomalies (2), and normal (9). Bile was aspirated during routine endoscopic retrograde cholangio pancreatography (ERCP) or percutaneous transhepatic cholangiography (PTC). DNA was prepared freshly from a native aliquot. p53 mutations were detected by polymerase chain reaction (PCR) for exons 5 through 8 followed by TGGE. PCR for ras mutations was performed as RFLP-PCR with sequencing. In four cases, mutations in p53 could be found in exons 6 and 7. Twenty-two samples showed ras mutations; ras mutations were found in choledocholithiasis (4/28), bile duct (5/21), gall bladder (3/8) and pancreatic (1/11) carcinoma, liver metastasis (3/3), ulcerative colitis (2/3), PSC (1/2), and chronic pancreatitis (1/16). Cytology was clearly positive in seven cases, suspicious in three other, inconclusive in six, and negative in the rest. The molecular analysis resulted in a sensitivity of 33% and specificity of 87%, respectively, for the diagnosis of a malignant condition. PCR for p53 and ras mutations may aid the diagnosis of primary and secondary (metastatic) hepatobiliary disease if a malignant condition of the bile ducts and the liver is suspected and cytology is inconclusive or negative. However, the incidence of p53 and ras mutations in bile seems less frequent than in other malignant conditions of the gastrointestinal tract and the pancreas and lower than in tissue, leaving a poor sensitivity and specificity. Nevertheless, the presence of a p53 and/or ras mutation per se supports a clinical suspicion of malignancy, even when the conventional cytology is negative or inconclusive.

[Anisakiasis of the stomach--a case report from Germany]

Anisakiasis or "herring worm disease" is one of the most important parasitic diseases of the gastrointestinal tract in Japan. In 1988 Lorenz and Warzok published 8 cases of intestinal anisakiasis in Eastern Germany. In 1988 Spehn et al. reported a case of gastric anisakiasis in an AIDS patient. Here, we describe a case of gastric anisakiasis in Germany with an impressive serious clinical course. The symptoms--acute abdominal cramps, severe chest pain, diarrhoea, sub-febrile temperatures and leucocytosis--followed 4 h after consumption of raw herring, which was homemade pickled in vinegar. The conventional and the endoscopic ultrasonography showed a thickened gastric wall made of mainly thickened submucosa. The larvae of Anisakis in the gastric mucosa were found and extracted endoscopically. Acute and severe abdominal pain after eating raw fish is an indication for early gastroscopy. The endoscopical extraction of possible larvae is the only effective therapy, as anthelmintics against nematodes (mebendazole, albendazole, thiabendazole) are ineffective.

p53 mutational spectra are different between squamous-cell carcinomas of the lip and the oral cavity

We studied the p53 mutational spectra of 34 lip and 60 intra-oral squamous-cell carcinomas and examined possible etiological and prognostic correlations for these tumor sites. For the p53 analysis of exons 5-8, we used PCR/TGGE screening followed by DNA sequencing. Mutations were found in 18/34 (53%) lip and 22/60 (38%) intra-oral carcinomas. The p53 mutational spectrum of the intra-oral carcinomas comprised transitions and transversions in nearly equal frequency (11 to 10). In comparison, transitions were 3.5 times more frequent than transversions (14 to 4) in carcinomas of the lip. The predominant types of base change found in intra-oral tumors were G:C-to-T:A transversions and G:C-to-A:T transitions (32% each), while in lip tumors G:C-to-A:T transitions (70%) were the most frequent. The rate of lip tumors with mutations was higher in non-smokers (8/13) than in smokers (9/20). In contrast, p53 mutations in intra-oral tumors clustered in smokers (18/47 vs. 2/10). G:C-to-T:A transversions, regarded as tobacco smoke-associated in lung cancer, were found in 2 moderate and 4 heavy smokers with intra-oral cancer. This base substitution was found in none of our lip cancers. In lip tumors, a high rate of mutations occurred at dipyridine sites (13/18); among these were 8 C-to-T transitions and 1 CC-to-TT tandem base transition. These changes are characteristic of DNA damage caused by UV light. The presence of mutational events at the DNA-binding surface of the p53 protein may correlate with poor clinical outcome. However, we could not find any statistically significant correlations between p53 status and survival. Only the recurrence-free interval was significantly shortened in cases with mutations affecting residues of the DNA-binding surface of the p53 protein.

Anal verrucous carcinoma and penile condylomata acuminata

A 50-year-old man presented with recurrent tumorous lesions on the penis and the anal region. The anal lesion was histologically diagnosed as verrucous carcinoma (VC) and the penile lesions were in line with condylomata acuminata. Samples taken from tumors of both sites were human papillomavirus (HPV) DNA positive. Two of them taken from the penis and the perianal region scored HPV DNA 6 positive by using polymerase chain reaction and the Southern blot method. Treatment of both VC and condylomata acuminata consisted in surgery and adjuvant immune therapy. Neither tumor recurrence nor metastases occurred up until 6 months after therapy.

High-performance liquid chromatographic assay with a simple extraction procedure for sensitive quantification of mycophenolic acid in rat and human plasma

We describe a novel sensitive and simplified gradient HPLC assay for quantification of the immunosuppressant mycophenolic acid (MPA) in rat and human plasma. In contrast to previously reported MPA assays, our method used a single step extraction comprising addition of acetonitrile, which contained phenolphthalein glucoronic acid as internal standard, for protein precipitation. Linearity: 0.1-100 microg/ml (r2>0.999), mean recoveries: MPA 98.0%, internal standard 105.2%, mean intra-day precision: 4.3%, mean day-to-day precision: 4.3%, mean day-to-day accuracy: -1.5%. Sensitivity was sufficient to allow for quantification of mycophenolic acid in as little as 50 microl plasma.

[p53 mutations and HPV infections in squamous epithelial carcinomas of the head-neck region. Long-term follow-up]

Mutations of the p53 gene are the most commonly observed genetic alterations in malignant tumors and are often associated with a loss of the tumor suppressor function of the p53 protein. We have analyzed specimens of head and neck squamous cell carcinomas (HNSCC) from 110 patients for p53 gene mutations and 92 of them additionally for human papillomavirus (HPV) infection in order to evaluate the prognostic significance of these factors by comparison with clinical follow-up data. Using the method of polymerase chain reaction (PCR)/temperature gradient gel electrophoresis (TGGE), mutations within the exons 5 to 8 of the p53 gene were found in 48 tumors (44%). Sequencing revealed missense mutations in most cases (15/20). Frequency of p53 gene mutations was not related to the tumor stage, the grade of differentiation, the presence of lymph node metastases, or the smoking history of the patients. With the help of a highly sensitive PCR/hybridization assay, an infection with the high-risk HPV types 16 and 18 could be detected in 39/92 tumor specimens (42%). Follow-up data were obtained from 99 patients with a range of 2-112 months. No correlation of overall survival on the presence of p53 gene mutations or HPV infection could be observed. The absence of statistically significant correlations between p53 gene mutations and progressive disease, however, does not exclude its putative relevance in early phases of tumor development.

p53 gene mutations and HPV infection in primary head and neck squamous cell carcinomas do not correlate with overall survival: a long-term follow-up study

We analyzed specimens of head and neck squamous cell carcinomas (HNSCC) from 110 patients for p53 gene mutations, and 92 of them for human papillomavirus (HPV) infection, in order to evaluate the prognostic significance of these factors by comparison with clinical follow-up data. Mutations within the exons 5 to 8 of the p53 gene were found in 48 tumors (44%). Sequencing revealed in most cases mis-sense mutations (16/21). Frequency of p53 gene mutations was not related to the tumor stage or the presence of lymph node metastases. Of the 46 tumors that were analyzed by immunohistochemistry, 26 stained positively (56%). The number of positively stained nuclei increased slightly with decreasing differentiation of the tumors, whereas no correlation was found between tumor stage and immunoreactivity. An infection with the high-risk HPV types 16 and 18 could be detected in 39/92 tumor specimens (42%). Follow-up data were obtained from 99 patients within a range of 2 to 112 months. No dependence of overall survival on the presence of p53 gene mutations or HPV infection could be observed. The absence of statistically significant correlations between p53 gene mutation and progressive disease, however, does not deny its putative relevance in early phases of tumor development.

HPV DNA and p53 alterations in oropharyngeal carcinomas

We have examined a series of 37 oropharyngeal squamous cell carcinomas for the presence of HPV 6/11, 16, and 18 DNA by polymerase chain reaction (PCR)/Southern blotting and for p53 alterations by immunohistochemistry and mutation screening with temperature gradient gel electrophoresis (TGGE). HPV sequences were found in a total of 26 of 37 cancers (70.3%), most frequently HPV 16 (20/37) followed by HPV 18 (11/37). Double infections with HPV 16 and 18 were present in 5 tumours. p53 accumulation was detectable immunohistochemically in 21 of 37 carcinomas (56.8%). There were remarkable differences in the distribution of immunoreactive tumour cells in relation to the tumour grade. A mutation screening for p53 by TGGE, directed to the amplified exons 5-8, revealed p53 mutations in 14 of 37 carcinomas (37.8%). Mutations in two different exons were present in 3 tumours, 11 tumours being hit once. Exon 7 was mutated in 6 carcinomas, exons 5 and 8 in 4 cases, and exon 6 in 3 cases. When grouping the tumours with p53 mutation according to their HPV state, HPV-positive cases showed slightly more mutations (11/26) than HPV-negative cases (3/11). Only 5 of 37 carcinomas (13.5%) contained neither HPV DNA nor p53 alterations. Our results indicate that high-risk HPV and p53 mutations frequently coexist in oropharyngeal carcinomas, in contrast to genital tumours, notably carcinomas of the cervix uteri. This may reflect different pathways in carcinogenesis in squamous cell epithelium from different sites.

Immunohistochemical and glycohistochemical localization of the beta-galactoside-binding S-type lectin in human placenta

The localization of the beta-galactoside binding lectin was studied immunohistochemically on acetone-fixed cryostat sections of full-term placental tissue using a biotinylated monoclonal antibody and glycohistochemically applying biotinylated asialofetuin and lactosylated bovine serum albumin. On blots of placental tissue lysates the lectin is recognized by the biotinylated lactosylated bovine serum albumin. The glycoconjugate recognition of the lectin on blots was inhibited in the presence of 0.1 M lactose showing the specificity of the interactions. The anti-lectin monoclonal antibody stained syncytiotrophoblast and trophoblastic cells. Both reagents applied for glycohistochemistry stained syncytiotrophoblast and trophoblastic cells of placental villi and the trophoblastic layer of extraplacental membranes. A strong uniform cytoplasmic staining was characteristic for syncytiotrophoblast and to a lower extent for cytotrophoblastic cells. The localization of the lectin is discussed with respect to a possible immunosuppressive function.

Human papillomavirus DNA in oral squamous cell carcinomas and normal mucosa

Human papillomavirus (HPV) infections in oral carcinomas and normal oral mucosa were studied by consensus primer screening and typing for HPV types 6/11, 16 and 18 DNA. After polymerase chain reaction (PCR) the DNA species of interest were identified by Southern blot hybridization with digoxigenin-labeled oligonucleotide probes. Frozen tissue and scrapings were equally suitable for HPV testing and yielded high HPV detection rates in carcinomas. By comparison, HPV analysis of paraffin-embedded material was much less efficient. HPV were demonstrated in 61.5% (16/26) of oral squamous cell carcinomas, high risk HPV 16 and 18 being the preferential types. The frequency of HPV detection in non-neoplastic mucosa of tumor patients decreased clearly with increasing distance from the tumor (range 26.9-3.8%) suggesting focal HPV infections. In contrast, normal buccal mucosa of a group of healthy volunteers contained HPV DNA only in 1% (1/97).

[p53 alterations and HPV status in oral squamous cell carcinomas]

Immunohistochemical examination of p53 protein accumulation, analysis of the p53 gene using amplification of the exons 5-8 followed by TGGE, and PCR based HPV typing were carried out on 40 oral squamous cell carcinomas. 28 of 40 oral carcinomas (70%) contained DNA of the oncogenic HPV types 16 and 18. A p53 accumulation was present in 20 of 37 tumors (54%). Mutations of the p53 gene were detected in 15 of 39 carcinomas (38%). 15 of 20 oral carcinomas with abnormal p53 expression and 11/15 tumors with mutations of the p53 gene were HPV positive. Our results demonstrate a frequent occurrence of p53 abnormalities in HPV positive oral squamous cell carcinomas. This pattern is divergent from HPV related genital carcinomas and could reflect differences in the etiology of squamous cell carcinomas of different sites.

[Clinical aspects, diagnosis and therapy of cancer of Vater's ampulla]

The carcinoma of the papilla occupies a special position among the periampullary carcinomas by its favourable prognosis. Responsible for this are the early appearance of symptoms due to the close neighbourhood to the common bile duct and the restriction of the metastasation to the first stage of lymphatic nodes in the majority of cases. Symptoms are jaundice, epigastric pain and decrease of weight. In the carcinoma of the papilla the duodenoscopy with biopsy and ERCP is the method of choice. The reliability of the biopsy is larger, when it is performed after an endoscopic sphincterotomy. For the delimitation of the carcinoma of the papilla against other causes can further be used the hypotensive duodenography, the abdominal computerd tomography, the sonography and the PTC. A curative treatment is possible only surgically. On account of the better long-term results the partial duodenopancreatectomy is to be preferred to the local exstirpation of the papilla. Endoscopic drainages of the biliary tract carried out preoperatively may reduce the lethality of operations. A palliative drainage of the biliary tract on the endoscopic or percutaneous transhepatic way as well as the endoscopic sphincterotomy may improve the patients' quality of life and prolong the survival time, when there are non-resectable tumours or a general inoperability.

Diffuse gastric antral vascular ectasia: cause of chronic gastrointestinal blood loss

In a patient with long-standing iron deficiency anemia, diffuse gastric antral vascular ectasia was found endoscopically. Diagnostic problems were the misinterpretation of the macroscopic finding as hemorrhagic inflammation and the microscopic confirmation of the diagnosis from small biopsy particles. Resection of the antrum resulted in a persistent normalization of hematologic parameters. Focal ischemia due to microthrombi in mucosal vessels might be the cause of the tendency of this vascular malformation to bleed.