Preoperative assessment of retrorectal tumours

Background

Retrorectal tumours present diagnostic and surgical challenges. This study aimed to identify whether preoperative imaging and/or biopsy provide diagnostic accuracy.

Methods

A consecutive series of patients who had undergone excision of a retrorectal tumour were identified from a database (2002–2013). Details of patient demographics, preoperative presentation, imaging, biopsy, surgical procedure, and gross and microscopic pathology were reviewed. Preoperative imaging and/or biopsies were compared with eventual pathology findings.

Results

In total, 76 patients were identified, all of whom had undergone preoperative cross-sectional imaging whereas only 22 had preoperative biopsy. Imaging correctly discriminated benign from malignant tumours in 72 of the 76 patients (specificity 97 per cent, sensitivity 88 per cent, positive predictive value 88 per cent and negative predictive value 97 per cent). The corresponding values for preoperative biopsy (benign versus malignant) were 100, 83, 100 and 93 per cent. None of the four patients who were assessed incorrectly as having benign or malignant disease on imaging would have undergone an alternative procedure had this been known before surgery. Preoperative biopsy did not significantly influence patient management, and the absence of preoperative biopsy had no detrimental effect; a definitive preoperative histological diagnosis would not have influenced subsequent management.

Conclusion

Preoperative imaging was accurate in the assessment of retrorectal tumours, whereas biopsy did not add to the surgical strategy.

Antigenic sites on ribonuclease A. Synthetic peptides corresponding to the sites 37-42 and 83-88 on ribonuclease A show immunogenicity

Two hexapeptides NH2-Lys-Asp-Arg-Cys-Lys-Pro-COOH and NH2-Asp-Cys-Arg-Glu-Thr-Gly-COOH corresponding to the strong hydrophilic regions 37-42 and 83-88, respectively, on ribonuclease A were synthesized by solid-phase method. These synthetic peptides showed antigenic characteristics and provided an experimental validity to the prediction made earlier, supporting the view that highly hydrophilic regions on the protein have a good correlation with their being potentially antigenic.

Studies on the enzymatic and physicochemical behaviour of the trichloroacetic acid-treated and untreated bovine pancreatic ribonuclease

Exposure of ribonuclease A to 5% trichloroacetic acid inactivates the enzyme partially. One of the possible reasons for such inactivation might be the exposure of one of the buried tyrosyl groups to the outside surface of the molecule (Sagar and Pandit (1983) Biochim. Biophys. Acta 743, 303-309). The trichloroacetic acid-treated enzyme hydrolysed 2':3'-cCMP with an efficiency of about 60%; while with rRNA as substrate, it is about 45%. Results indicate that apart from the reduction in the activity on trichloroacetic acid treatment, the enzyme possesses a reduced ability to break down the secondary structures of substrates such as rRNA in the first phase of the reaction. Thermal unfolding of ribonuclease A was followed by various physicochemical techniques such as UV absorbance, CD-spectroscopy and differential scanning microcalorimetry. The results indicate that the enzyme, after trichloroacetic acid-treatment, has a less ordered structure when compared to that of untreated enzyme. Thermal unfolding profiles reveal that trichloroacetic acid-treated ribonuclease A, like the untreated enzyme, follows a one-step transition with relatively lower transition temperature (Tm). NMR-spectral data suggests perturbations in the histidyl environment at the active site.

Denaturation studies on bovine pancreatic ribonuclease. Effect of trichloroacetic acid

Exposure of ribonuclease (EC 3.1.27.5) to 5% trichloroacetic acid solution is found to partially inactivate the enzyme. This inactivation is a function of time of exposure to trichloroacetic acid and reaches a plateau of about 45% residual activity. Higher concentrations of trichloroacetic acid lead to greater inactivation. Physicochemical properties such as sedimentation coefficient, gel-filtration behaviour and polyacrylamide gel electrophoresis of the trichloroacetic acid-treated enzyme remain unaffected as compared to the untreated enzyme. However, spectrophotometric titration of the trichloroacetic acid-treated enzyme revealed that one of the three 'buried' groups of tyrosine is exposed to the outside surface of the molecule. Near ultraviolet CD spectra supported these observations. Far ultraviolet CD spectra suggested some refolding of the enzyme after trichloroacetic acid treatment. Immunological determinants on the molecule remain unaltered upon trichloroacetic acid treatment. It is concluded that the exposed tyrosine group may be causing a conformational change in the protein and this change may be indirectly responsible for the observed reduction in the activity after trichloroacetic acid treatment.