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Biomedical subjects

M Lenz

Publications and source records attributed to M Lenz.

At least 19 recordsLinked to original sources
PubMed1992

Isolation, sequencing and expression in E. coli of the urocanase gene from white clover (Trifolium repens).

The urocanase gene was detected in a clone obtained from a genomic library of white clover. The entire gene has been sequenced and expressed in the pT7-7/E. coli BL 21 (DE 3) system. The deduced sequence of the plant urocanase is 72% homologous with that of the well-characterized urocanase from Pseudomonas putida. The purification procedure, as well as kinetic and electrophoretic behaviour, of the new enzyme are described.

Amino Acid Sequence↗
PubMed1992

Computed tomography (CT) and magnetic resonance imaging (MRI) in T-stage evaluation of oral and oropharyngeal carcinomas.

174 CT and 32 MRI investigations were carried out on patients with carcinomas of the mouth and oropharynx. The methods were compared and their value in predicting the pre-therapeutic T-staging studied. The combination of CT and clinical examination was able to improve the T-staging considerably compared with clinical examination alone. MRI was superior to CT in delineating the tumour margins in 78% of patients. T1-weighted and gradient echo sequences after intravenous gadolinium injection were particularly useful. Nevertheless, T-staging based on clinical and CT-findings was changed in only 5% of patients by MRI. MRI is especially useful in T1 tumours and in cancer of the base of the tongue. MRI should also be used instead of CT were dental fillings obscure the region of interest. If there are good MRI facilities and an experienced team available MRI can be used before CT.

Diagnostic Errors↗
PubMed1991

[Diagnosis and therapy of aggressive fibromatosis (extra-abdominal desmoid) in the head and neck area].

Desmoid tumours (extraabdominal desmoids, aggressive fibromatosis) are rare connective tissue tumours, that grow infiltratively and destructively. The analysis of the course of disease in three patients suffering from desmoid tumours in the head and neck region (regio submandibularis, regio parotidea, parapharyngeal space) confirmed the data in literature that painless swelling and dysfunction are the first non-specific signs of the disease. Morphologically reactive fibromatosis and fibrosarcoma should be considered (amongst others) in differential diagnosis. CT and MR scans are useful in determining the extent of the tumours and help to distinguish the tumour from nerves, vessels and bone. Surgery is the therapy of choice in the head and neck region. Primary surgery was performed in our patients. Due to recurrences two of our patients have been operated on several times including major plastic reconstructive surgery. One patient died three and a half years after primary treatment due to sarcomatous degeneration. A large parapharyngeal recurrence was successfully reduced by percutaneous radiation therapy in our second patient. Follow-up of our third patient was NAD 15 months after resection of a large parapharyngeal/mediastinal process including blocking of two cervical vertebrae. Summing up, desmoid tumours are rare connective tissue tumours in the head and neck region with a destructive biological behaviour similar to malignant tumours and a high recurrence rate. Surgery is the treatment of choice. In recurrences or if the tumour is not properly resectable, radiation must be considered, whereas the chemotherapeutical approach is not yet well established.

Adult↗
PubMed1991

Overcorrection as an academic remediation procedure. A review and reappraisal.

Overcorrection procedures traditionally were designed to reduce the behavioral excesses of persons with mental retardation. However, beginning with a study of Foxx and Jones (1978), it became clear that variations of the procedure could be used to enhance academic proficiency in students with average intelligence, borderline intelligence, learning disabilities, and various levels of mental retardation. Studies were reviewed in this article that have used overcorrection procedures to enhance academic proficiency, and it was concluded (a) that overcorrection, alone or combined with positive reinforcement, significantly increased the academic proficiency of the students, and (b) that the label "overcorrection" is inappropriate, given that the procedures described in these studies did not meet the criteria for overcorrection procedures. It was suggested that overcorrection procedures used for academic remediation be called directed rehearsal in the future to reflect more accurately the procedures actually used.

Achievement↗
PubMed1991

[Computed tomography of the soft tissue of the neck. Lymph node metastases and their differential diagnosis].

Computed tomography is considered as the method of choice concerning N-staging in patients with known malignant tumours of the head and neck region. The application of an intravenous contrast medium (50 ml as a bolus, 100 ml as a fast infusion) is obligatory. In lesions of the neck with unknown histology the plain CT scan is important followed by the application of contrast medium, optional in form of a dynamic sequential CT. Calcifications, the densities pre and post contrast medium application, the curve of enhancement and the structure of the lesion are the important criteria of differential diagnosis.

Diagnosis, Differential↗
PubMed1991

Imaging of the oropharynx and oral cavity.

Imaging methods play a significant role in the diagnosis of oropharynx and oral cavity lesions. Contrast-enhanced CT has been established as the baseline technique for T- and N-staging of malignomas. CT yields significant additional information to clinical methods, especially in examining large tumors. With an examination time of only 10 minutes, it is the method of choice. MR imaging requires more time (40 minutes or more) but the superior tissue contrast allows the depiction of smaller lesions. The use of fast gradient-echo sequences in combination with the application of gadolinium diethylenetriamine penta-acetic acid offers new perspectives. High-resolution real-time ultrasound in the hands of an experienced examiner may be helpful because it is easily available; however, it does not allow a complete tumor staging.

Diagnostic Imaging↗
PubMed1990

[The clinical value of contrast CT in lymph node staging in the neck region].

Pre-treatment CT examinations of 333 patients with squamous carcinomas in the head and neck region have been analysed. Two hundred and six patients had lymph-node metastases and lymph-node staging was ascertained. The criteria for metastatic involvement were lymph node size greater than 15 mm. and changes in structure (inhomogeneity, central hypodensity and ring enhancement). CT had a sensitivity of 93% and accuracy of 89%. This was better than palpation (sensitivity 64%, accuracy 72%). CT can be regarded as a reliable basis for treatment planning.

Adolescent↗
PubMed1990

[T-staging of tongue and mouth floor tumors: comparison of ultrasonography and computerized tomography].

A comparison was made between the pretherapeutic CT and ultrasound findings of 43 patients with tumors of the oral tongue and the floor of the mouth. Two tumors of the edge of the tongue (T1) each were not diagnosed by computed tomography and by sonography. In three cases a more precise determination of the tumor size was achieved by sonography. In 25 out of 38 cases the contrast between tumor and sound tissue was better in the sonographic image. The reduction and regressive modification of the tumor following to radiotherapy could be observed in eleven cases. Despite the benefits of sonographic investigation in this area due to the excellent contrast without any need of contrast media, the good availability and the absence of metal and movement artefacts, this method is not able to replace computed tomography. The most important disadvantages of sonography were found to be the incapability to show osseous erosions and the restricted or lacking possibility to assess the parapharyngeal and the retropharyngeal area.

Adult↗
PubMed1990

[Computed tomography of the soft tissues of the neck. Lymph node metastases and their differential diagnosis. I. Methods and the principal CT criteria for lymph node metastases].

Standardisation of the examination method is imperative to guarantee reproducible and valid assessability of the cervical lymph node status. To this end, update high-resolution CT equipment of the third generation will be suitable, provided it meets certain minimum requirements, such as: 120 kV, 280 mAs, 480 projections over 360 degrees, 4-5 mm slice thickness, continuous tomography. If a primary tumour is known to exist, no plain examination is needed. The decisive examination is effected after intravenous administration of contrast medium in a dosage of 2.0-2.5 ml contrast medium/kg body weight (assuming a body weight of 70 kg, this would amount to 150 ml = 45 g iodine), one-third of the total dosage to be given as bolus and two-thirds as a rapid infusion. This procedure ensures sharp definition of lymph nodes against vessels and musculature over the entire period of examination. If tumour anamnesis has been established the size of the lymph node is significant for assessing the lymph node status. Even lymph node metastases less than 15 mm can be properly identified if the structure of the lymph nodes is known and employed as a criterion (central hypodensity with rim enhancement, inhomogeneity).

Carcinoma, Squamous Cell↗