Stability of infundibular dilatations: a single center follow-up study and systematic review of the literature

PURPOSE

Although infundibular dilatations (IDs) have been thought to be benign anatomical variants, case reports suggest that they can grow and rupture. The aim of this study was to determine whether IDs have a tendency to grow or rupture.

METHODS

The study population was collected from the Tampere University Hospital (TAUH) Aneurysm Database. The presence of IDs was screened from the medical records and imaging studies of 356 intracranial aneurysm patients left to follow-up from 2005 to 2020. The imaging studies were reviewed to confirm the IDs, and their clinical course. Finally, we performed a systematic review of published cases of ID leading to aneurysmatic rupture from PubMed.

RESULTS

We found 97 typical IDs in 83 patients and 9 preaneurysmal lesions resembling ID in 9 patients. Out of the typical cone-shaped IDs, none grew or ruptured in a total follow-up of 409 patient-years. One preaneurysmal lesion ruptured during a follow-up: this lesion had components of both infundibular dilatation and aneurysm at the beginning of follow-up. In the systematic literature search, we found 20 cases of aneurysmatic SAHs originating from an ID. Of those, only 7 had imaging available prerupture. All 7 IDs were typically cone-shaped, but a branching vessel originating from the apex of ID was only seen in 4/7.

CONCLUSION

Typical infundibular dilatations seem to be benign anatomical variants that are stable and, thus, do not need prophylactic treatment or imaging follow-up. Likely, the SAHs reported from IDs were actually caused by misdiagnosed preaneurysmal lesions.

Less is more - The Finnish Prehospital Stroke Scale prospective validation

OBJECTIVES

The current bifurcation of the acute stroke care pathway requires prehospital separation of strokes caused by large vessel occlusion. The first four binary items of the Finnish Prehospital Stroke Scale (FPSS) identify stroke in general, while the fifth binary item alone identifies stroke due to large vessel occlusion. The straightforward design is both easy for paramedics and statistically beneficial. We implemented FPSS based Western Finland Stroke Triage Plan, including medical districts of a comprehensive stroke center and four primary stroke centers.

PATIENTS AND METHODS

The prospective study population was consecutive recanalization candidates transported to the comprehensive stroke center within the first six months of implementing the stroke triage plan. Cohort 1 consisted of n=302 thrombolysis- or endovascular treatment candidates transported from the comprehensive stroke center hospital district. Cohort 2 comprised ten endovascular treatment candidates transferred directly to the comprehensive stroke center from the medical districts of four primary stroke centers.

RESULTS

In Cohort 1, FPSS sensitivity for large vessel occlusion was 0.66, specificity 0.94, positive predictive value 0.70, and negative predictive value 0.93. Of the ten Cohort 2 patients, nine had large vessel occlusion, and one had an intracerebral hemorrhage.

CONCLUSIONS

FPSS is straightforward enough to be implemented in primary care services to identify candidates for endovascular treatment and thrombolysis. When used by paramedics, it predicted two-thirds of large vessel occlusions with the highest specificity and positive predictive value reported to date.

Finnish flow diverter study: 8 years of experience in the treatment of acutely ruptured intracranial aneurysms

Background

Flow diversion of acutely ruptured intracranial aneurysms (IAs) is controversial due to high treatment-related complication rates and a lack of supporting evidence. We present clinical and radiological results of the largest series to date.

Methods

This is a nationwide retrospective study of acutely ruptured IAs treated with flow diverters (FDs). The primary outcome was the modified Rankin Scale (mRS) score at the last available follow-up time. Secondary outcomes were treatment-related complications and the aneurysm occlusion rate.

Results

110 patients (64 females; mean age 55.7 years; range 12–82 years) with acutely ruptured IAs were treated with FDs between 2012 and 2020 in five centers. 70 acutely ruptured IAs (64%) were located in anterior circulation, and 47 acutely ruptured IAs (43%) were blister-like. A favorable functional outcome (mRS 0–2) was seen in 73% of patients (74/102). Treatment-related complications were seen in 45% of patients (n=49). Rebleeding was observed in 3 patients (3%). The data from radiological follow-ups were available for 80% of patients (n=88), and complete occlusion was seen in 90% of aneurysms (79/88). The data from clinical follow-ups were available for 93% of patients (n=102). The overall mortality rate was 18% (18/102).

Conclusions

FD treatment yields high occlusion for acutely ruptured IAs but is associated with a high risk of complications. Considering the high mortality rate of aneurysmal subarachnoid hemorrhage, the prevention of rebleeding is crucial. Thus, FD treatment may be justified as a last resort option.

In-Hospital Intravenous Thrombolysis Offers No Benefit in Mechanical Thrombectomy in Optimized Tertiary Stroke Center Setting

Purpose

Mechanical thrombectomy (MT) is the first-line treatment in acute stroke patients presenting with large vessel occlusion (LVO). The efficacy of intravenous thrombolysis (IVT) prior to MT is being contested. The objective of this study was to evaluate the efficacy of MT without IVT in patients with no contraindications to IVT presenting directly to a tertiary stroke center with acute anterior circulation LVO.

Materials and Methods

We collected the data of 106 acute stroke patients who underwent MT in a single high-volume stroke center. Patients with anterior circulation LVO eligible for IVT and directly admitted to our institution who subsequently underwent MT were included. We recorded baseline clinical, laboratory, procedural, and imaging variables and technical, imaging, and clinical outcomes. The effect of intravenous thrombolysis on 3-month clinical outcome (mRS) was analyzed with univariate tests and binary and ordinal logistic regression analysis.

Results

Fifty-eight out of the 106 patients received IVT + MT. These patients had 2.6-fold higher odds of poorer clinical outcome in mRS shift analysis (p = 0.01) compared to MT-only patients who had excellent 3-month clinical outcome (mRS 0–1) three times more often (p = 0.009). There were no significant differences between the groups in process times, mTICI, or number of hemorrhagic complications. A trend of less distal embolization and higher number of device passes was observed among the MT-only patients.

Conclusions

MT without prior IVT was associated with an improved overall three-month clinical outcome in acute anterior circulation LVO patients.

Supplementary Information

The online version of this article (10.1007/s00270-020-02727-8) contains supplementary material, which is available to authorized users.

Functional imaging with 11C-metomidate PET for subtype diagnosis in primary aldosteronism

OBJECTIVE

Endocrine Society guidelines recommend adrenal venous sampling (AVS) in primary aldosteronism (PA) if adrenalectomy is considered. We tested whether functional imaging of adrenal cortex with 11C-metomidate (11C-MTO) could offer a noninvasive alternative to AVS in the subtype classification of PA.

DESIGN

We prospectively recruited 58 patients with confirmed PA who were eligible for adrenal surgery.

METHODS

Subjects underwent AVS and 11C-MTO-PET without dexamethasone pretreatment in random order. The lateralization of 11C-MTO-PET and adrenal CT were compared with AVS in all subjects and in a prespecified adrenalectomy subgroup in which the diagnosis was confirmed with immunohistochemical staining for CYP11B2.

RESULTS

In the whole study population, the concordance of AVS and 11C-MTO-PET was 51% and did not differ from that of AVS and adrenal CT (53%). The concordance of AVS and 11C-MTO-PET was 55% in unilateral and 44% in bilateral PA. In receiver operating characteristics analysis, the maximum standardized uptake value ratio of 1.16 in 11C-MTO-PET had an AUC of 0.507 (P = n.s.) to predict allocation to adrenalectomy or medical therapy with sensitivity of 55% and specificity of 44%. In the prespecified adrenalectomy subgroup, AVS and 11C-MTO-PET were concordant in 10 of 19 subjects with CYP11B2-positive adenoma and in 6 of 10 with CYP11B2-positivity without an adenoma.

CONCLUSIONS

The concordance of 11C-MTO-PET with AVS was clinically suboptimal, and did not outperform adrenal CT. In a subgroup with CYP11B2-positive adenoma, 11C-MTO-PET identified 53% of cases. 11C-MTO-PET appeared to be inferior to AVS for subtype classification of PA.

Anemia Predicts Poor Clinical Outcome in Mechanical Thrombectomy Patients with Fair or Good Collateral Circulation

Background and Purpose

Anemia predicts poor clinical outcome of ischemic stroke in the general stroke population. We studied whether this applies to those treated with mechanical thrombectomy for proximal anterior circulation occlusion in the setting of differing collateral circulation.

Methods

We collected the data of 347 consecutive anterior circulation stroke patients who underwent mechanical thrombectomy after multimodal CT imaging in a single tertiary stroke care center. Patients with occlusion of the internal carotid artery and/or the first segment of the middle cerebral artery were included. We recorded baseline clinical, laboratory, procedural, and imaging variables, and the technical, imaging, and clinical outcomes. Differences between anemic and nonanemic patients were studied with appropriate statistical tests and binary logistic regression analysis.

Results

Ninety-four out of the 285 patients eligible for analysis had anemia, and 243 had fair or good collateral circulation (collateral score, CS, >0). Fifty-four percent of the patients experienced good 3-month clinical outcome (modified Rankin Scale ≤2). In pooled analyses of the CS 1–4 and 2–4 ranges, nonanemic patients had good clinical outcome significantly more often (p < 0.001 for both). This effect was not seen in patients with poor collateral circulation (CS = 0). Nonanemic patients had significantly better odds of good clinical outcome (OR = 2.6, 95% CI 1.377–5.030, p = 0.004) in a binary regression model. A 0.1 g/dL increase in hemoglobin improved the odds of good clinical outcome by 2% (OR = 1.02, 95% CI 1.002–1.044, p = 0.03).

Conclusions

Low hemoglobin on admission predicts poor clinical outcome in mechanical thrombectomy patients with fair or good collateral circulation.

Oral Bacterial Signatures in Cerebral Thrombi of Patients With Acute Ischemic Stroke Treated With Thrombectomy

Background

Chronic infections have been reported to be risk factors for both coronary heart disease and ischemic stroke. DNA of oral bacteria, mainly from the viridans streptococci group, has been detected in coronary thrombus aspirates of myocardial infarction and cerebral aneurysms. Viridans streptococci are known to cause infective endocarditis and possess thrombogenic properties. We studied the presence of oral bacterial DNA in thrombus aspirates of patients with acute ischemic stroke treated with mechanical thrombectomy.

Methods and Results

Thrombus aspirates and arterial blood were taken from 75 patients (69% men; mean age, 67 years) with acute ischemic stroke. The presence of Streptococcus species, mainly the Streptococcus mitis group, belonging to viridans streptococci as well as Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans in samples were determined using a quantitative polymerase chain reaction with specific primers and probes. The relative amount of bacterial DNA in a sample was determined with the comparative threshold cycle method. Bacterial DNA was detected in 84% (n=63) of aspired thrombi, and 16% (n=12) of samples were considered bacterial DNA negative. DNA of Streptococcus species, mainly the S mitis group, was found in 79% (n=59) of samples. The median relative amount of Streptococcus species DNA was 5.10‐fold higher compared with the control blood samples from the same patients. All thrombi were negative for both P gingivalis and A actinomycetemcomitans.

Conclusions

This is the first study showing the common presence of bacterial DNA from viridans streptococci in aspired thrombi of patients with acute ischemic stroke. Streptococcal bacteria, mostly of oral origin, may contribute to the progression and thrombotic events of cerebrovascular diseases.

Urine colour as an indicator for anastomotic leakage after robot-assisted radical prostatectomy

Objectives: To determine whether macroscopic haematuria predicts urethrovesical anastomotic leakage after robot-assisted laparoscopic radical prostatectomy (RALP) as well as a cystogram.Patients and methods: Participants were recruited before cystogram and catheter removal 5-14 days after RALP surgery. Urine colour in the collection bag was classified according to a three-step scale (clear, light red and dark red) and leakages in cystogram were graded with a four-step scale (Grade 0-3). Diagnostic accuracy parameters were calculated for urine colour. A multivariate logistic regression model was used to evaluate other leakage risk factors.Results: Of 214 patients, 201 (94%) had clear, six (3%) had light red and seven (3%) had dark red coloured urine. In the cystogram, 20 (9%) patients had leakage; 14 had Grade 1, five Grade 2 and one Grade 3 leakage. Overall, specificity and sensitivity of urine colour in predicting anastomotic leakage were 0.97 (95% CI = 0.95-100) and 0.38 (95% CI = 0.17-0.59), respectively. Negative and positive predictive values were 94% and 62%, respectively. Other significant risk factors for anastomotic leakage were previous transurethral resection or radiation therapy to the prostate, non-waterproof anastomosis at surgery, postoperative pelvic haematoma, long catheterization and surgeon's inexperience. In patients with no other risk factors, test sensitivity improved to 0.80 (95% CI = 0.45-1.15) and negative and positive predictive values to 99% and 44%, respectively.Conclusion: This prospective single-arm trial indicates that in patients with clear urine and no other risk factors for anastomotic leakage, a cystogram examination before urethral catheter removal can be safely omitted.

Carotid Artery Stenosis Is Associated with Better Intracranial Collateral Circulation in Stroke Patients

BACKGROUND

Adequate collateral circulation improves the clinical outcome of ischemic stroke patients. We evaluated the influence of ipsilateral carotid stenosis on intracranial collateral circulation in acute stroke patients.

METHODS

We collected the data of 385 consecutive acute stroke patients who underwent mechanical thrombectomy after multimodal computed tomography (CT) imaging in a single high-volume stroke center. Patients with occlusion of the first segment (M1) segment of the middle cerebral artery were included. We recorded baseline clinical, laboratory, procedural, and imaging variables and technical, imaging, and clinical outcomes. The effect of carotid stenosis on intracranial collateral circulation was studied with appropriate statistical tests and ordinal regression analysis.

RESULTS

Fifty out of the 247 patients eligible for analysis had severe ipsilateral carotid stenosis (≥75%). These patients were 4-times more likely to have very good intracranial collaterals (Collateral Score 3-4, p = 0.001) than the nonstenotic and slightly stenotic (<75%) patients. The severely stenotic patients had a longer mean operation time (41 vs. 29 min to reperfusion, respectively, p = 0.001). Nevertheless, 54% of severely stenotic patients had good 3-month clinical outcome (modified Rankin Scale ≤2) with no significant difference between the 2 groups.

CONCLUSIONS

Carotid artery stenosis of over 75% of vessel diameter was associated with better intracranial collateral circulation of patients with acute ischemic stroke. This did not significantly change the 3-month clinical outcome.

Chronic Infarcts Predict Poor Clinical Outcome in Mechanical Thrombectomy of Sexagenarian and Older Patients

BACKGROUND

The impact of lacunar and cortical chronic ischemic lesions (CILs) on the clinical outcome of mechanical thrombectomy (MT) has been little studied. Clinical trials suggest that older patients benefit from MT. We investigated the effect of CILs on the clinical outcome of sexagenarian and older patients with acute middle cerebral artery (MCA) or distal internal carotid artery (ICA) stroke who received MT to treat large-vessel occlusion (LVO).

METHODS

We prospectively collected the clinical and imaging data of 130 consecutive MT patients of which 68 met the inclusion criteria. We limited the analysis to sexagenarian and older subjects and occlusions no distal than the M2 segment. Baseline clinical, procedural and imaging variables, technical outcome, 24-hour imaging outcome, and the clinical outcome were recorded. Differences between patients with and without CILs were studied with appropriate statistical tests and binary logistic regression analysis.

RESULTS

Twenty-one patients (31%) had at least 1 CIL. Thirty-eight percent of patients with CIL(s) compared with 62% without (P = .06) experienced good clinical outcome (3-month modified Rankin Scale ≤ 2). A similar nonsignificant trend was seen when lacunar lesions, lesion multiplicity, and chronic white matter lesions were examined separately. Absence of CIL increased the odds of good clinical outcome 3.7-fold (95% confidence interval 1.0-10.7, P = .05) in logistic regression modeling.

CONCLUSIONS

Chronic cortical and lacunar infarcts in admission imaging are associated with poor clinical outcome in sexagenarian and older patients treated with MT for LVO of the MCA or distal ICA.

Internal Carotid Artery and the Proximal M1 Segment Are Optimal Targets for Mechanical Thrombectomy

Background and Purpose

Mechanical thrombectomy (MT) is an established treatment of acute anterior circulation stroke caused by large vessel occlusion (LVO). We compared the clinical outcome (3-month modified Rankin Scale, mRS) in hyperacute (<3h from the onset of symptoms) ischemic stroke between an MT and an intravenous thrombolysis (IVT) cohort in proximal (ICA and the proximal M1 segment of the middle cerebral artery) and distal (the distal M1 and the M2 segment) LVOs.

Methods

We prospectively reviewed 67 patients who underwent MT with newer-generation stent retrievers. The IVT cohort consisted of 98 patients who received IVT without MT. We recorded baseline clinical, procedural and imaging variables, technical outcome, 24-h imaging outcome, and the clinical outcome. Differences between the groups were studied with theoretically appropriate statistical tests and binary logistic regression analysis.

Results

The proportion of patients who had a proximal LVO and experienced good (mRS ≤2) or excellent (mRS ≤1) clinical outcome was significantly larger in the MT group (62 vs. 7%, p < 0.001; 47 vs. 3%, p < 0.001, respectively). In a regression model including relevant confounding variables, good clinical outcome was seen significantly more often among patients with proximal occlusions (OR = 6.0, CI 95% 1.9-18.3, p = 0.002). In a similar model, no statistically significant differences were observed in patients with more distal occlusions.

Conclusions

MT is superior to IVT in achieving good clinical outcome in hyperacute anterior circulation stroke in the most proximal occlusions (ICA and proximal M1 segment). In the distal M1 and M2 segments neither of these therapies clearly outperforms the other.

TREVO and Capture LP have equal technical success rates in mechanical thrombectomy of proximal and distal anterior circulation occlusions

PURPOSE

Mechanical thrombectomy (MT) is a proven method to treat large vessel occlusions in acute anterior circulation stroke. We compared the technical, imaging, and clinical outcomes of MT performed with either TREVO or Capture LP devices.

METHODS

There were 42 and 43 patients in the TREVO and Capture LP groups, respectively. Baseline variables, technical outcome (Thrombolysis In Cerebral Infarction, TICI), 24 hours imaging outcome, and 3-month clinical outcome (modified Rankin Scale, mRS) were prospectively recorded. The patients were stratified according to clot location, groups compared, and logistic regression models devised to study the effect of device selection on the clinical outcome.

RESULTS

The technical success rates were equal in both proximal (internal carotid artery and proximal M1 segment) and distal occlusions (distal M1 and M2 segments). The proportion of TICI 2b or 3 was 96% and 87% with TREVO and 87% and 89% with Capture LP (p=0.25 and p=0.80, respectively). Device selection did not significantly predict good clinical outcome (mRS ≤2) in either proximal or distal occlusions. In multivariate analysis, selecting Capture LP borderline significantly increased the odds of an excellent outcome close to sixfold both in proximal and distal occlusions (OR 6.7, 95% CI 0.82 to 53.7, p=0.08 and OR 5.7, 95% CI 0.88 to 37.8, p=0.07, respectively).

CONCLUSIONS

TREVO and Capture LP perform equally well in proximal and distal occlusions in the anterior circulation when technical and good clinical outcome are considered. Capture LP may have a small advantage in reaching mRS ≤1 at 3 months. However, this needs to be confirmed in a randomized study.

Preoperative white matter lesions are independent predictors of long-term survival after internal carotid endarterectomy

Background

Cerebral white matter lesions (WMLs) predict long-term survival of conservatively treated acute stroke patients with etiology other than carotid stenosis. In carotid endarterectomy patients, WMLs are associated with severe carotid stenosis and unstable plaques, with the risk of perioperative complications and with increased 30-day perioperative risk of death. However, no data exist on their effect on postoperative long-term survival, a factor important when considering the net benefit from carotid endarterectomy. Whether this effect is independent of classical risk factors and indications for surgery is not known either. We hypothesized that WMLs could be evaluated from preoperative routine computed tomography (CT) scans and are predictors of postoperative survival, independent of classical cardiovascular risk factors, indication category and degree of carotid stenosis.

Methods

A total of 353 of 481 (73.4%) consecutive patients subjected to carotid endarterectomy due to different indications, i.e. asymptomatic stenosis (n = 28, 7.9%), amaurosis fugax (n = 52, 14.7%), transient ischemic attack (n = 135, 38.2%) or ischemic stroke (n = 138, 39.1%), from prospective vascular registries during the years 2001-2010 with digital preoperative CT scans, were included in the study. WMLs were rated by a radiologist (Wahlund criteria) in a blinded fashion. Internal carotid artery (ICA) stenoses were angiographically graded (<50, 50-69, 70-99 and 100%). Odds ratios (ORs) and hazard ratios (HRs) are reported (ORs and HRs ≤1 indicate a beneficial effect). The median follow-up time was 67 months (interquartile range 45.5, range 0-129 months). Spearman's rho was used to estimate intraobserver agreement. Binary logistic regression was performed to analyze the association of risk factors with WMLs. Cox regression proportional hazards analysis was used to study the effect of different factors on survival.

Results

WML severity could be assessed with a substantial intraobserver agreement (Spearman's rho 0.843, p < 0.0001). Only age (OR 1.10, 95% CI 1.06-1.15; p < 0.0001 per year), degree of ipsilateral ICA stenosis (OR 2.22, 95% CI 1.08-4.55; p < 0.05 per stenosis grade) and indication category (OR 1.63, 95% CI 1.19-2.24; p < 0.01 per category) remained independently associated with WMLs. Age (HR 1.04, 95% CI 1.01-1.08; p < 0.05 per year), diabetes (HR 1.59, 95% CI 1.01-2.49; p < 0.05), peripheral arterial disease (HR 2.47, 95% CI 1.46-4.15; p < 0.01), degree of ipsilateral ICA stenosis (HR 2.56, 95% CI 1.12-5.87; p < 0.05 per stenosis grade) and WMLs (HR 3.83, 95% CI 1.17-12.5; p < 0.05) remained independently associated with increased long-term mortality.

Conclusions

WMLs in a preoperative CT scan provide a substantially reliable estimate of postoperative long-term survival of carotid endarterectomy patients independent of currently used criteria, i.e. cardiovascular risk factors, indication category and degree of ipsilateral ICA stenosis.

[Mechanical thrombectomy in the treatment of acute disturbance of cerebral circulation]

An essential aim of acute treatment of brain infarction is to restrict the size of the infarct by rapid and permanent recanalization of the obstructed artery. Thrombolytic therapy based on intravenous administration of alteplas (IV-tPA) exhibits the highest efficacy in the treatment of cerebral artery thrombi that are fairly small or intermediate in size. Intra-arterial thrombolysis (IA-tPA) and mechanical thrombectomy can be considered, if IV-tPA turns out to be ineffective or is contraindicated. In situations where the expected effect of IV-tPA:n is modest per se, mechanical thrombectomy should be taken into account as part of the therapeutic strategy.

Keratinocyte growth factor stimulates migration and hyaluronan synthesis in the epidermis by activation of keratinocyte hyaluronan synthases 2 and 3

Keratinocyte growth factor (KGF) activates keratinocyte migration and stimulates wound healing. Hyaluronan, an extracellular matrix glycosaminoglycan that accumulates in wounded epidermis, is known to promote cell migration, suggesting that increased synthesis of hyaluronan might be associated with the KGF response in keratinocytes. Treatment of monolayer cultures of rat epidermal keratinocytes led to an elongated and lifted cell shape, increased filopodial protrusions, enhanced cell migration, accumulation of intermediate size hyaluronan in the culture medium and within keratinocytes, and a rapid increase of hyaluronan synthase 2 (Has2) mRNA, suggesting a direct influence on this gene. In stratified, organotypic cultures of the same cell line, both Has2 and Has3 with the hyaluronan receptor CD44 were up-regulated and hyaluronan accumulated in the epidermis, the spinous cell layer in particular. At the same time the expression of the early differentiation marker keratin 10 was inhibited, whereas filaggrin expression and epidermal permeability were less affected. The data indicate that Has2 and Has3 belong to the targets of KGF in keratinocytes, and support the idea that enhanced hyaluronan synthesis acts an effector for the migratory response of keratinocytes in wound healing, whereas it may delay keratinocyte terminal differentiation.

Hyaluronan bound to CD44 on keratinocytes is displaced by hyaluronan decasaccharides and not hexasaccharides

Abundant hyaluronan is present between epidermal keratinocytes. However, virtually nothing is known regarding its organization in the limited extracellular space between these cells. We have used metabolic labeling with [3H]glucosamine and [35S]sulfate and a hyaluronan-specific biotinylated probe to study the metabolism of hyaluronan and its localization in monolayer cultures of a rat epidermal keratinocyte cell line. Hyaluronan (approximately 20 fg/cell) was present on the apical and lateral surfaces of the cells in two nearly equal pools, either in patches (approximately 160/cell) or diffusely spread. The hyaluronan in the patches is bound to CD44 as indicated by co-localization with an antibody to CD44, and by displacement with hyaluronan decasaccharides as well as with an antibody that blocks hyaluronan binding to CD44. The inability of hyaluronan oligomers shorter than 10 monosaccharides to displace hyaluronan suggests that CD44 dimerization or cooperative interactions are required for tight binding. The diffuse hyaluronan pool is likely bound to hyaluronan synthase during its biosynthesis.