Simultaneous quantum dash-well emission in a chirped dash-in-well superluminescent diode with spectral bandwidth >700 nm

We report on the quantitative evidence of simultaneous amplified spontaneous emission from the AlGaInAs/InAs/InP-based quantum-well (Qwell) and quantum-dashes (Qdash) in a multistack dash-in-an-asymmetric-well superluminescent diode heterostructure. As a result, an emission bandwidth (full width at half-maximum) of >700 nm is achieved, covering entire O-E-S-C-L-U communication bands, and a maximum continuous wave output power of 1.3 mW, from this device structure. This demonstration paves a way to bridge entire telecommunication bands through proper optimization of device gain region, bringing significant advances and impact to a variety of cross-disciplinary field applications.

On the phenomenon of large photoluminescence red shift in GaN nanoparticles

We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100 nm. Nanoparticles with broad tunable emission wavelength from 362 to 440 nm have been achieved by exciting the samples using the excitation power-dependent method. We attribute this large wavelength tunability to the localized potential fluctuations present within the GaN matrix and to vacancy-related surface states. Our results show that GaN NPs fabricated using this technique are promising for tunable-color-temperature white light-emitting diode applications.

A possible approach on optical analogues of gravitational attractors

In this paper we report on the feasibility of light confinement in orbital geodesics on stationary, planar, and centro-symmetric refractive index mappings. Constrained to fabrication and [meta]material limitations, the refractive index, n, has been bounded to the range: 0.8 ≤ n(r[combining arrow]) ≤ 3.5. Mappings are obtained through the inverse problem to the light geodesics equations, considering trappings by generalized orbit conditions defined a priori. Our simulation results show that the above mentioned refractive index distributions trap light in an open orbit manifold, both perennial and temporal, in regards to initial conditions. Moreover, due to their characteristics, these mappings could be advantageous to optical computing and telecommunications, for example, providing an on-demand time delay or optical memories. Furthermore, beyond their practical applications to photonics, these mappings set forth an attractive realm to construct a panoply of celestial mechanics analogies and experiments in the laboratory.

Generation of J0-Bessel-Gauss beam by a heterogeneous refractive index map

In this paper, we present the theoretical studies of a refractive index map to implement a Gauss to a J(0)-Bessel-Gauss convertor. We theoretically demonstrate the viability of a device that could be fabricated on a Si/Si(1-y)O(y)/Si(1-x-y)Ge(x)C(y) platform or by photo-refractive media. The proposed device is 200 μm in length and 25 μm in width, and its refractive index varies in controllable steps across the light propagation and transversal directions. The computed conversion efficiency and loss are 90%, and -0.457 dB, respectively. The theoretical results, obtained from the beam conversion efficiency, self-regeneration, and propagation through an opaque obstruction, demonstrate that a two-dimensional (2D) graded index map of the refractive index can be used to transform a Gauss beam into a J(0)-Bessel-Gauss beam. To the best of our knowledge, this is the first demonstration of such beam transformation by means of a 2D index-mapping that is fully integrable in silicon photonics based planar lightwave circuits (PLCs). The concept device is significant for the eventual development of a new array of technologies, such as micro optical tweezers, optical traps, beam reshaping and nonlinear beam diode lasers.

Two-step controllable electrochemical etching of tungsten scanning probe microscopy tips

Dynamic electrochemical etching technique is optimized to produce tungsten tips with controllable shape and radius of curvature of less than 10 nm. Nascent features such as "dynamic electrochemical etching" and reverse biasing after "drop-off" are utilized, and "two-step dynamic electrochemical etching" is introduced to produce extremely sharp tips with controllable aspect ratio. Electronic current shut-off time for conventional dc "drop-off" technique is reduced to ∼36 ns using high speed analog electronics. Undesirable variability in tip shape, which is innate to static dc electrochemical etching, is mitigated with novel "dynamic electrochemical etching." Overall, we present a facile and robust approach, whereby using a novel etchant level adjustment mechanism, 30° variability in cone angle and 1.5 mm controllability in cone length were achieved, while routinely producing ultra-sharp probes.

Room temperature strong coupling effects from single ZnO nanowire microcavity

Strong coupling effects in a dielectric microcavity with a single ZnO nanowire embedded in it have been investigated at room temperature. A large Rabi splitting of ~100 meV is obtained from the polariton dispersion and a non-linearity in the polariton emission characteristics is observed at room temperature with a low threshold of 1.63 μJ/cm(2), which corresponds to a polariton density an order of magnitude smaller than that for the Mott transition. The momentum distribution of the lower polaritons shows evidence of dynamic condensation and the absence of a relaxation bottleneck. The polariton relaxation dynamics were investigated by time-resolved measurements, which showed a progressive decrease in the polariton relaxation time with increase in polariton density.

Effect of the number of stacking layers on the characteristics of quantum-dash lasers

A theoretical model is evaluated to investigate the characteristics of InAs/InP quantum dash (Qdash) lasers as a function of the stack number. The model is based on multimode carrier-photon rate equations and accounts for both inhomogeneous and homogeneous broadenings of the optical gain. The numerical results show a non monotonic increase in the threshold current density and a red shift in the lasing wavelength on increasing the stack number, which agrees well with reported experimental results. This observation may partly be attributed to an increase of inhomogeneity in the active region.

418 cases of laparoscopic colorectal resections: a single-institution experience and literature review

INTRODUCTION

Evidence from randomised controlled trials has shown that laparoscopic colon and rectal cancer resection not only confers short-term benefits but also does not differ considerably in terms of its long-term oncological outcomes, as compared with open surgery.

METHODS

All laparoscopic colon and rectal resections performed between January 2005 and December 2007 were included. Patient records were reviewed from a prospective database and the relevant clinical data was obtained, with a subgroup analysis of cancer procedures performed.

RESULTS

418 patients (247 male), median age 63 years (range 24 to 88), underwent laparoscopic resection of the colon and rectum. The median Body Mass Index (BMI) was 22.5 (range 13.5 to 39.3). The majority of the procedures were performed for malignant disease (81.3 percent) and the most common procedure was anterior resection (79.4 percent). The median duration of surgery was 135 minutes (range 65 to 330), with conversions to open surgery in 44 patients (10.5 percent). Complications occurred in 78 patients (18.7 percent), including anastomotic leaks in five (1.20 percent). The median length of hospital stay was five days (range 3 to 90) and the median follow-up was 19 months (range 1 to 46). In the 340 patients with malignant disease, the median number of lymph nodes harvested was 13 (range 5 to 48), and at the latest review, 230 patients (67.6 percent) were disease-free, with locoregional recurrence in 2.9 percent and systemic recurrence in 10 percent.

CONCLUSION

To date, this is the largest series of laparoscopic colorectal resections reported locally, and our results show that it is safe, feasible and produces favourable results.

Radiation proctitis: a decade's experience

INTRODUCTION

Pelvic radiotherapy is an essential component of potentially curative therapy for many pelvic malignancies; however, the rectum consequently often sustains collateral injury.

METHODS

The researchers retrieved patient data that was prospectively gathered over a ten-year period between January 1995 and December 2004. The relevant details, including gender, age, pelvic pathology for which radiotherapy was administered, the presenting symptoms, the interval between radiotherapy and the onset of symptoms, the mode of diagnosis, treatments received, length of hospital stay and duration of follow-up, were analysed.

RESULTS

During the period under review, 77 patients were admitted for the treatment of radiation proctitis, with a median follow-up period of 14 (range 1-61) months. There were 23 male and 54 female patients, with a median age of 63.9 (range 37-89) years. The most common underlying cancers were gynaecological (63.6 percent), prostate (18.2 percent) and colorectal (15.6 percent) cancer. The most common presenting symptom was bleeding per rectum (89.6 percent), with a change in bowel habits a distant second (10.4 percent). The median latent period between the completion of radiotherapy and the onset of symptoms was 24 (range 3-68) months. The majority of the patients (72.5 percent) received non-surgical treatment, most commonly using topical 4 percent formalin solution to arrest the bleeding, with more than half the patients requiring repeat treatments. 14 (18.2 percent) patients required colorectal resections for intractable bleeding, intestinal obstruction or intra-abdominal sepsis.

CONCLUSION

Radiation proctitis can be a therapeutic challenge, even in the most experienced hands. The majority of patients who present with per rectal bleeding can be treated using topical modalities, while surgery may offer the only chance of relief from life-threatening symptoms.

Optical injection modulation of quantum-dash semiconductor lasers by intra-cavity stimulated Raman scattering

We report the optical injection modulation of semiconductor lasers by intra-cavity stimulated Raman scattering. This mechanism manifests itself as sharply enhanced modulation bandwidth in InAs/InGaAlAs/InP quantum-dash lasers when the injected photons are 33 +/- 3 meV more energetic than the lasing photons. Raman scattering measurements on the quantum-dash structure and rate equation models strongly support direct gain modulation by stimulated Raman scattering. We believe this new bandwidth enhancement mechanism may have important applications in optical communication and signal processing.

Robotic-assisted surgery for low rectal dissection: from better views to better outcome

INTRODUCTION

The use of robotics in colorectal surgery is relatively new. The first few cases of colonic surgery using da Vinci Surgical System were reported in 2002. Since then, several centres had reported on their experience, with favourable outcomes. Our department started to embark on robotics in colorectal surgery in December 2007. The aim of our paper was to share our early experience with robotics in colorectal surgery and provide an update on the current status of robotics.

METHODS

Preparations included formal training with the da Vinci Surgical System, certification of the surgeons, and obtaining Hospital Ethics committee approval. We used a hybrid technique of laparoscopic and robotic assistance in the resection of mid- to low-rectal cancer (total mesorectal excision). Laparoscopic approach was used to isolate the inferior mesenteric artery and for mobilisation of the left colon. The da Vinci robot was used in the dissection of the rectum down to the pelvic floor. We reviewed the outcomes of our early experience with emphasis on feasibility and safety.

RESULTS

Over a period of three months, we performed eight cases of robotic-assisted colorectal surgery for cancer. The median age of the patients was 55 (range 42-80) years. The median operating time was 192.5 (range 145-250) minutes. There were no intraoperative or postoperative complications related to the use of robotics. The median length of hospital stay was five (range 4-30) days.

CONCLUSION

Robotic-assisted laparoscopic colorectal surgery is a safe and feasible procedure.

Colorectal cancer mass screening event utilising quantitative faecal occult blood test

INTRODUCTION

Colorectal cancer (CRC) is a leading cause of morbidity and mortality with human and financial costs. Screening by faecal occult blood test (FOBT) has proven to be effective in decreasing mortality from CRC in both randomised trials and case-control studies. We report on the results of a CRC screening event using quantitative FOBT (QFOBT) held in Singapore.

METHODS

The mass screening event was held over two days, and participants 40 years or older without prior screening performed in the preceding year were eligible. Those with significant symptoms or medical comorbidities were excluded. Stool sampling was done with two issued immunochemical QFOBT kits, and participants with positive stool samples with equal or greater than 100 ng haemoglobin/ml sample solution in any two samples were advised to have a colonoscopy screening conducted.

RESULTS

A total of 1,048 participants took part in the screening event. 222 (21 percent) of the participants claimed to have some abdominal symptoms prior to screening. 49 participants (26 males, 23 females) tested positive for QFOBT and 47 were evaluated. 10 (21 percent) had polyps and one case of colorectal cancer was detected. Seven of these cases had significant neoplasia (lesions 1 cm or larger) and were treated. Two patients required surgery.

CONCLUSION

Our study demonstrates wide variation in the attitudes of participants who turned up for screening. In addition, the number of significant colorectal neoplasia patients (14 percent) in those with positive QFOBT provides further evidence of the importance of screening with a potential reduction in CRC mortality. Continuous education of the public in events such as this, is essential to improving attitudes towards screening.

Laparoscopic high anterior resection with natural orifice specimen extraction (NOSE) for early rectal cancer

Laparoscopic surgery for colorectal cancer requires an abdominal incision to extract the resected specimen. We describe a technique for laparoscopic resection of an early-stage upper rectal cancer in a 51-year-old man followed by transanal specimen delivery, hence avoiding the need for making any additional abdominal incisions for retrieval of the specimen. Pneumoperitoneum was created, followed by medial-tolateral mobilization of the sigmoid colon, and take down of the splenic flexure and division of the inferior mesenteric vessels laparoscopically. The upper rectum distal to the tumour and proximal colon was transected with a laparoscopic stapler. The specimen was retrieved transanally via an opening in the rectal stump. The proximal colon was then delivered transanally and the anvil of the circular stapler inserted before returning it to the pelvic cavity. The rectal stump was transected again just below the opening to close off the stump, and the colorectal anastomosis was then completed intracorporeally. The patient, a 51-year-old male (BMI 18.6 kg/m(2)) with a 2.5-cm, early-stage posterior rectal cancer 12 cm from the anal verge, underwent the above-described procedure. Postoperative recovery was uneventful. He resumed normal daily activities 1 week after surgery. Histology confirmed a T1N0 upper rectal cancer. In the effort to minimize surgical trauma and postoperative pain, natural orifice specimen extraction techniques have been attempted. This procedure may be applicable to benign tumours and early colorectal cancer, and serves as an intermediate step between laparoscopic and natural orifice surgery.

A 6-year review of surgical morbidity and oncological outcome after high anterior resection for colorectal malignancy with and without splenic flexure mobilization

OBJECTIVE

High anterior resection (HAR) for colorectal cancer is traditionally performed with routine mobilization of the splenic flexure. This is a retrospective review of mortality and morbidity following HAR in which the splenic flexure has been preserved.

METHOD

From a prospective database, all patients who had undergone elective HAR for colorectal cancer between 1999 and 2005 were identified. Morbidity, mortality, pathology and survival data for patients having HAR with and without splenic flexure mobilization were analysed.

RESULTS

A total of 707 patients were identified. Five hundred and thirty-one had HAR with preservation of the splenic flexure. In these patients outcome was: anastomotic leak (0.4%), wound infection (3.6%), anastomotic stricture (0.4%) and 30-day mortality (0.9%). No statistical significant difference was found for postoperative morbidity (P = 0.1926), 30-day mortality (P =0.3285), lymph node harvest (P = 0.2127) or survival (P = 0.1457) compared with patients in whom the splenic flexure was mobilized. Longitudinal resection margins were greater following HAR with splenic flexure mobilization (P < 0.0001).

CONCLUSION

No morbidity, oncological or survival disadvantage in performing splenic flexure preserving HAR was found.

Comparison of forearm and conventional Bier's blocks for manipulation and reduction of distal radius fractures

Forearm-based Bier's block has been advocated as a useful anaesthesic technique in hand surgery. However, there is limited data comparing forearm blocks with the conventional Bier's block. We conducted a randomised controlled trial (n=30) comparing the two techniques of anaesthesia for manipulation and reduction of closed distal radius fractures in an emergency room setting. Pain scores measured using the Visual Analogue Scale during the procedure were used as the primary outcome assessment. There was no significant difference in pain scores between the forearm and conventional Bier's block (mean VAS 18.4 SD 22.10 versus 33.7 SD 29.6). No major complications were observed in either group. The forearm-based Bier block is an effective alternative to the conventional block.

Room-temperature broadband emission of an InGaAs/GaAs quantum dots laser

We report the first demonstration to our knowledge of an ultrabroad emission laser using InGaAs/GaAs quantum dots by cycled monolayer deposition. The device exhibits a lasing wavelength coverage of approximately 40 nm at an approximately 1160 nm center wavelength at room temperature. The broadband signature results from the superposition of quantized lasing states from highly inhomogeneous dots.

Prospective randomized crossover trial comparing fibre with lactulose in the treatment of idiopathic chronic constipation

BACKGROUND

Fibre is often recommended as the first-choice treatment but its effects can be uneven. The aim of the study was to compare the clinical efficacy and tolerability of fibre versus lactulose in outpatients with chronic constipation.

METHODS

In a prospective randomized crossover trial, patients were randomized to receive fibre or lactulose for four weeks. Between treatments, patients had at least one week free of laxatives.

RESULTS

50 patients, of median age 50 years (range, 18-85) were recruited and 39 patients completed the trial. Compared to fibre, lactulose resulted in significantly higher mean bowel frequency (7.3, 95% CI 5.7 to 8.9 vs. 5.5, 95% CI 4.4 to 6.5; p=0.001) and stool consistency score (3.4, 95% CI 3.1 to 3.7 vs. 2.9, 95% CI 2.5 to 3.3; p=0.018). Scores for ease of evacuation were similar. The frequencies of adverse effects were not significantly different, but greater in the lactulose group. Mean patients' recorded improvement score was significantly higher after taking lactulose than fibre (6.2, 95% CI 5.5 to 7.0 vs. 4.8, 95% CI 4.0 to 5.9; p=0.017). Of the 39 patients who completed the trial, 24 (61.5%) preferred lactulose and 14 (35.9%) preferred fibre.

CONCLUSIONS

Lactulose had better efficacy than fibre for chronic constipation in ambulant patients, although both treatments were equally well tolerated in terms of adverse effects.

The outcome after restorative proctocolectomy with or without defunctioning ileostomy

PURPOSE

Controversy exists regarding the safety for omission of diverting ileostomy in restorative proctocolectomy because of fears of increased septic complications. This study was designed to evaluate the outcomes of restorative proctocolectomy in a consecutive series of patients by comparing postoperative complications, functional results, and quality of life in patients with and without diverting ileostomy.

METHODS

Data regarding demographics, length of stay, surgical characteristics, and complications were reviewed and recorded according to the presence (n= 1,725) or absence (n = 277) of a diverting ileostomy at the time of pelvic pouch surgery. Criteria for omission of ileostomy included: stapled anastomosis, tension-free anastomosis, intact tissue rings, good hemostasis, absence of airleaks, malnutrition, toxicity, anemia, and prolonged consumption of steroids. Functional outcome and quality of life indicators were prospectively recorded and compared.

RESULTS

Patients in the ileostomy group had greater body surface area and older mean age at time of surgery, were taking greater doses of steroids preoperatively, and required more blood transfusions at the time of surgery compared with the one-stage (P < 0.05). There were no differences between the two groups in septic complications (P > 0.05). Early postoperative ileus was more common in the one-stage group (P < 0.001). There were no differences between the groups in quality of life and functional outcomes.

CONCLUSIONS

For carefully selected patients undergoing restorative proctocolectomy with ileal pouch-anal anastomosis, omission of diverting ileostomy is a safe procedure that does not lead to an increase in septic complications or mortality. Quality of life and functional results are similar to those who undergo ileal pouch-anal anastomosis with diversion, provided that certain selection factors are considered.

PPH03 stapled hemorrhoidopexy: our experience

BACKGROUND

Stapled hemorrhoidopexy is an established treatment for hemorrhoidal disease. We evaluated our experience with stapled hemorrhoidopexy using the new Procedure for Prolapse and Hemorrhoids (PPH03) Proximate HCS hemorrhoidal circular stapler (Ethicon Endo-Surgery).

METHODS

We retrospectively reviewed clinical data for 238 patients who had undergone stapled hemorrhoidopexy in our department over a 2-month period. Patients were followed-up for a median of 3.5 weeks (range, 1-11 weeks) and were analyzed for complications and resolution of symptoms.

RESULTS

The hemorrhoids treated were third- and fourth-degree, as well as second degree (after failure of other therapies). Mean duration of surgery was 12.7 minutes (range, 5-20 minutes) and the majority of patients was treated with an ambulatory procedure. Most patients were discharged within 6 hours after surgery. On follow-up, 3.7% of patients had minor complaints after surgery. Technically, the new PPH03 stapler device has a quickclose knob, which allows rapid opening and closing. The closed staple height of 0.75 mm increases staple line compression on tissue and key blood vessels, hence minimizing bleeding. Prior to this, stapled hemorrhoidopexy was done using the PPH01 device.

CONCLUSIONS

Stapled hemorrhoidopexy using the new PPH03 stapler is a safe, short and effective procedure in the management of hemorrhoids. It can be done in the ambulatory setting and patients have few postoperative complications.

Minilaparotomy left iliac fossa skin crease incision vs. midline incision for left-sided colorectal cancer

BACKGROUND

Midline laparotomies offer excellent exposure but are associated with increased postoperative pain and longer recovery. A minilaparotomy resection of leftsided colorectal cancers was studied as an alternative approach.

PATIENTS AND METHODS

We performed a case-control retrospective review of 280 randomly selected patients (140 midline incisions; 140 left skin crease incisions) who underwent elective, curative resection of left-sided colorectal cancers.

RESULTS

Patients in both groups were of comparable age and sex. The left skin crease incision was shorter (median length, 13.5 cm) than the midline incision (median length, 20.0 cm). Median operation time was less in the left skin crease group (75 min) than in the midline incision group (105 min). Similar types of operations were performed, including left hemicolectomies, sigmoid colectomies, anterior resections and ultra-low anterior resections. Adequacy of resection was confirmed by histological analysis, with no involvement of margins. The median numbers of lymph nodes removed were comparable: 10 for the skin crease incision group and 12 for the midline incision group. Postoperative parameters for the skin crease incision group showed that feeding, ambulation, narcotic use and hospital stay were significantly better than the parameters in the midline group. Complications of intestinal obstruction were also reduced in the skin crease incision group.

CONCLUSIONS

The limited left skin crease incision provides adequate margins of clearance in colorectal cancers when compared to the midline incision, but has advantages of shorter operation time, earlier feeding and ambulation, and earlier discharge from hospital.

Endoscopic view of rectal amebiasis mimicking a carcinoma

We report the case of a 45-year-old man with rectal amebiasis, presenting with rectal bleeding and chronic diarrhea, confirmed on rectal biopsy. The endoscopic view was highly suggestive of a carcinoma and caused confusion about its etiology. The striking difference in the endoscopic view before and after medical therapy of the tumor-like lesion was remarkable. This case illustrates the importance of an accurate histologic diagnosis before definitive treatment and highlights the mimicry of rectal carcinoma by rectal amebiasis on endoscopy.

Portal vein thrombi after restorative proctocolectomy

BACKGROUND

Restorative proctocolectomy (RP) has been the surgical procedure of choice for surgical management of mucosal ulcerative colitis since 1978. This study was undertaken to investigate the clinical presentation and implications of portal vein thrombi (PVT).

METHODS

We reviewed all patients undergoing RP in our institution in the 4 years from January 1997 to December 2000. As the diagnosis of PVT was made on computed tomography (CT) scan in all cases, we confined our incidence estimate to those patients having an abdominal CT scan postoperatively. All scans were reviewed by an experienced radiologist. Patient demographics, symptoms, and clinical course were recorded.

RESULTS

A total of 702 patients underwent RP, of whom 94 had a CT scan within the postoperative period. PVT was diagnosed in 42 of the 94 patients (45%). PVT was diagnosed at initial reading of the scan in 11 patients, and on review in 31. The indications for CT scan included abdominal pain, fever, leukocytosis, and delayed bowel function. Septic complications of RP caused these symptoms and signs in 45 patients, 20 of whom had PVT. Twenty-two patients were found to have had PVT without evidence of any septic source.

CONCLUSION

PVT can be found in a high proportion of patients undergoing abdominal CT scan after RP. It is often associated with pain, fever, nausea vomiting, tenderness, and leukocytosis. This study shows that PVT subtle enough to go undiagnosed has no serious consequences, even when not treated. Also, patients treated with anticoagulation recover completely.

Primary colorectal signet-ring cell carcinoma in Singapore

BACKGROUND

Primary colorectal signet-ring cell carcinoma is a rare but distinctive tumour of the colon and rectum. The clinicopathological features are still controversial. The aim of this study is to review the clinicopathological features and management of this type of tumour in our hospital.

METHODS

The clinicopathological features and survival data of all cases of primary colorectal signet-ring cell carcinoma were reviewed retrospectively.

RESULTS

There were nine cases of primary colorectal signet-ring cell carcinoma in 3000 consecutive colorectal carcinoma patients seen from 1989 to 1999. There were seven male and two female patients with a mean age of 54.7 years. Three patients were younger than 40 years. The common presenting symptoms were rectal bleeding (33%) and small bowel obstruction (33%). Two (22%) patients required emergency surgery due to acute small bowel obstruction. The most common tumour location was the right colon (44%) followed by the rectum (33%). All nine patients presented at a very late stage of disease. A majority (77%) had Dukes' C disease while two (22%) had Dukes' D disease with distant dissemination. Peritoneal spread (33%) was the most frequent way of dissemination. There was no patient with liver metastases at the time of diagnosis and initial presentation. The mean survival time was 30 (range 5-108) months. The 5-year survival rate was 12%.

CONCLUSIONS

Primary colorectal signet-ring cell carcinoma is frequently diagnosed late with a very poor prognosis. A high incidence of peritoneal seeding and low incidence of liver metastases appears to be a characteristic of signet-ring cell carcinoma of the colon and rectum.