Comparison of depth of electrode insertion between cochleostomy and round window approach: a cadaveric study

INTRODUCTION

Round window approach and cochleostomy approach can have different depth of electrode insertion during cochlear implantation which itself can alter the audiological outcomes in cochlear implant.

OBJECTIVE

The current study was conducted to determine the difference in the depth of electrode insertion via cochleostomy and round widow approach when done serially in same temporal bone.

METHODOLOGY

This is a cross-sectional study conducted in the Department of Otorhinolaryngology in conjunction with Department of Anatomy and Department of Diagnostic and Interventional Radiology over a period of 1 year. 12-electrode array insertion was performed via either approach (cochleostomy or round window) in the cadaveric temporal bone. HRCT temporal bone scan of the implanted temporal bone was done and depth of insertion and various cochlear parameters were calculated.

RESULT

A total of 12 temporal bones were included for imaging analysis. The mean cochlear duct length was 32.892 mm; the alpha and beta angles were 58.175° and 8.350°, respectively. The mean angular depth of electrode insertion via round window was found to be 325.2° (SD = 150.5842) and via cochleostomy 327.350 (SD = 112.79) degree and the mean linear depth of electrode insertion via round window was found to be 18.80 (SD = 4.4962) mm via cochleostomy 19.650 (SD = 3.8087) mm, which was calculated using OTOPLAN 1.5.0 software. There was a statically significant difference in linear depth of insertion between round window and cochleostomy. Although the angular depth of insertion was higher in CS group, there was no statistically significant difference with round window type of insertion.

CONCLUSION

The depth of electrode insertion is one of the parameters that influences the hearing outcome. Linear depth of electrode insertion was found to be more in case of cochleostomy compared to round window approach (p = 0.075) and difference in case of angular depth of electrode insertion existed but not significant (p = 0.529).

Delayed post-operative aggravation of sleep related disturbances in patients of basilar invagination with Chiari malformation: case report and review of the literature

Sleep apnoea is common in patients with Basilar Invagination with Arnorld Chiari Malformation (ACM). Various studies have shown its incidence in the range of 60-70% among such patients. Most of the studies have shown improvement in sleep disturbances after decompressive surgeries for Chiari Malformations. There is no report of postoperative deterioration due to sleep apnoea in these patients. Authors report two cases of basilar invagination associated with ACM and Platybasia, who deteriorated probably due to worsening of pre-existing sleep disorders on 3rd and 7th postoperative days after their surgeries, despite clinico-radiological improvements during their early post-operative courses. Authors discuss literature related to sleep apnoea in basilar invagination associated with Chiari Malformations and share precautions, which are relevant and should be undertaken in such patients especially during early post-operative periods to avoid alarming complication which may occur even in experienced hands.

Programmed cell death ligand 1 (PD-L1) expression in non-small cell lung cancer: Findings from a tertiary care institute in western part of India

BACKGROUND

Immune checkpoint inhibitors targeting either programmed cell death protein 1 (PD-1) or programmed cell death ligand 1 (PD-L1) have been established as a novel target for immunotherapy in non-small cell lung cancer (NSCLC). Prevalence of PD-L1 expression in NSCLC varies from 13% to 70%, with sparse data from the Indian subcontinent. In this study, we looked at PD-L1 expression and its association with demographic, clinical, radiologic and pathologic parameters in NSCLC patients.

METHODS

This was an observational study carried over a period of 18 months in which 65 patients of NSCLC were included. Immunohistochemistry (IHC) for PD-L1 was done using an automated IHC stainer and testing was performed using PD-L1 IHC CAL10. For statistical analysis, unpaired t test, Chi square test, Fisher's exact test and binomial logistic regression were used. P < 0.05 was taken to be statistically significant.

RESULTS

Mean age of the patients was 62.9 ± 9.2 years, and majority (87.3%) of them were males. Seventeen (26.2%) patients expressed PD-L1, among whom 10 had high PD-L1 expression (≥50%) and 7 had low PD-L1 expression (1-49%). PD-L1 expression was seen in 13 out of 43 cases of squamous cell carcinoma (SCC) and 4 out of 15 cases of adenocarcinoma. On applying binomial logistic regression analysis, association between smoking and PD-L1 expression was found to be insignificant.

CONCLUSION

Almost a quarter of NSCLC cases were PD-L1 positive without any difference in expression between SCC and adenocarcinoma. PD-L1 status was not associated with any specific demographic, clinical or radiologic parameter including the histologic subtype.

Pediatric Renovascular Hypertension: A Pediatric Interventional Radiologist's Perspective

Renovascular hypertension (RVH) contributes close to one-fourth of the secondary etiologies of hypertension in children and a delay in diagnosis can result in adverse clinical outcomes. RVH in children is clinically silent with elevations in blood pressure measurements sometimes as its sole manifestation. Only a high index of suspicion by the clinician can prompt its detection. Despite the availability of other imaging modalities like ultrasound, computed tomography, and magnetic resonance imaging, digital subtraction angiography is still considered the gold standard to make a diagnosis of RVH. Angioplasty is considered the treatment of choice in appropriately selected patients. In this article, we shall focus on the various imaging findings, and management of RVH in children, which requires a multidisciplinary approach with a special focus on the role of interventional radiology.

Renal Allograft Malakoplakia Presenting as a Pseudotumoral Lesion

Malakoplakia is an uncommon inflammatory disease that can involve many organ systems but is often encountered in the urogenital tract. Kidney allograft malakoplakia is even rarer and can have a diffuse parenchymal or a pseudotumoral presentation. We describe a case of grafi malakoplakia in an adult female, who presented with dull aching pain in the right loin, fever, and vomiting. Ultrasonography of the kidney graft showed a heterogeneous lesion (2.6 cm × 2.9 cm), raising suspicion of primary or metastatic renal tumors. The diagnosis was established after a histopathological examination of the kidney biopsy. This pseudotumoral presentation of malakoplakia can mimic renal cell carcinoma, lymphoma, fungal infections, or tuberculosis. It is essential to perform a biopsy for establishing the diagnosis.

Systematic Review of Morphometric Analysis of Anterior Cerebral Artery (ACA) Emphasizing on Its Clinical Implications

Thorough data of morphometric measurements of arteries forming Circle of Willis (CW) is crucial for radiological and neurosurgical interventions. This systematic review has been conducted with the objective to find an effective range of length and diameter of anterior cerebral artery (ACA) and to observe whether there is any change in the length and diameter of ACA depending on age or sex. Articles based on length and diameter of ACA via any mode of study like cadaveric or radiological were considered in this systematic review. A comprehensive literature search using databases Cochrane Library, PubMed, and Scopus for relevant articles was done. Research papers which answered the focused questions were selected for data analysis. It was observed that the range of length and diameter of ACA were 8.1 mm-21 mm and 0.5 Å-3.4 mm, respectively. In majority of the studies, length and diameter of ACA were more in the younger age group (>40 years); and the length of ACA was more in females whereas the diameter of ACA was more in males. These data will be applicable for better construction and decipherment of angiographic images. This will help in the proper and guided treatment of intracranial pathologies.

Correlation of tibiofemoral joint-space width with the clinico-radiological scoring of knee osteoarthritis – a comparison between anteroposterior and lyon-schuss radiographic views

Background

The degree of joint space narrowing measured on radiographs provide a reliable estimate of the extent and severity of Osteoarthritis (OA) of the knee. While the standing antero-posterior (AP) view radiographs have been used traditionally, recent studies suggest that the Lyon-Schuss (LS) view is able to detect early OA changes better. The present study was, therefore, conducted to make an objective comparison between the two views with respect to their corelation with the patient's clinical and radiological scores.

Methods

Forty patients (80 knees) were included in this cross-sectional study. Medial as well as lateral tibiofemoral joint space widths (JSW) were measured using vernier callipers on printed, calibrated radiographic images. Knee Society Score (Function) (KSS-F) was used as the clinical outcome measure while Ahlbäck grade was used for determining radiological severity. JSW was correlated with KSS-F and the Ahlbäck grade using Spearman's rho correlation coefficient. Reproducibility of the method was assessed using the intra-class correlation coefficient (ICC).

Results

Average age of the participants was 60 ± 7.65 (range 50–78) years, with 18 males and 22 females. ICC for intraobserver reliability was 0.97 and for inter-observer reliability, was 0.91 (AP view) and 0.92 (LS view), respectively. Medial JSW measurements taken on the AP view were found to have a significantly higher degree of correlation with both KSS-F and Ahlbäck grade ( p  < 0.05) than those obtained from the LS view.

Conclusion

Although the LS view may be more sensitive for detecting early OA changes in knee, particularly in the lateral tibiofemoral compartment, the present study shows that AP view correlates better with the patient's overall clinical and radiological profile.

Large Vessel Occlusions By Free Floating Thrombi in Strokes During the COVID-19 pandemic- A Single Center Observational Study

BACKGROUND

An increased incidence of systemic macrothrombotic phenomena such as strokes has been observed in moderate and severe COVID. However, strokes have also been increasingly observed in mild COVID, post COVID, or without obvious COVID illness.

OBJECTIVE

To share our experience with a specific stroke type noted during the COVID pandemic period.

MATERIALS AND METHODS

A single-center observational study was conducted in Western India from January to December 2020, and data regarding stroke patients admitted under Neurology services were noted. Clinical, laboratory, and radiological characteristics of strokes and subtypes were documented.

RESULTS

A total of 238 stroke patients were admitted in 2020, 76.5% during the COVID pandemic period. Among 153 ischemic strokes, 16.3% and 56.2% had large vessel occlusion (LVO) in pre-COVID and COVID pandemic period, respectively. Of all ischemic strokes, 20.9% (18 patients) and 12% (3 patients) had free floating thrombus (FFT) in the COVID versus pre-COVID period, respectively. Only 44.4% of all FFT patients could be proven SARS-CoV-2 RT-PCR positive while 50% were COVID suspect with surrogate markers of heightened inflammation at time of stroke. All patients were given anticoagulation and average mRS at discharge was 3.1 (range: 1-6) and 1.84 (range: 0-4) at 3-month follow-up in survivors.

CONCLUSIONS

This study highlights the presence of FFT causing LVO as a new stroke subtype during the COVID-19 pandemic. With renewed and steeper spike in COVID-19 cases, especially new variants, the resurgence of this stroke subtype needs to be actively explored early in the course of illness to reduce morbidity and mortality.

Forgotten Chemo-Port Leading to Chylothorax: A Rare Presentation

Chylothorax is an uncommon cause of pleural effusion in routine clinical practice. Thoracic surgery, trauma and malignancy are the leading causes of chylothorax accounting for more than 90% of cases.1,2 We report this rare case of a middle aged lady with treated carcinoma breast who presented with left-sided chylothorax secondary to subclavian vein and superior vena cava thrombosis caused by a longstanding indwelling chemo-port in the right internal jugular vein. Patient was managed on total parenteral nutrition (TPN) leading to complete resolution of chylothorax.

Reducing mortality in mucormycosis of the head and neck in diabetic patients: A CARE case series

INTRODUCTION

Rhinocerebral mucormycosis is extremely fatal, with mortality rates ranging from 85-93% despite the best treatment in immunocompromised patients. We emphasize the importance of early diagnosis, repeated debridement, and aggressive antifungal treatment to reduce mortality.

CASE SUMMARY

We report six cases (five male and one female), with a mean age of 51 years who were diagnosed to have mucormycosis from 2017 to 2019. All patients were diabetic. Intracranial involvement and orbital involvement were found in four cases. Facial nerve palsy was seen in two cases, one without any apparent otological involvement. Aggressive serial debridement and amphotericin B was started. Posaconazole was added subsequently to the treatment in two cases. One patient succumbed to the disease five months after discharge. The other five patients are on regular follow-up for a mean duration of 14 months at the end of which two had residual disease which was under control.

DISCUSSION

Repeated surgical debridement with an early aggressive and combination antifungal therapy can result in good outcomes even in advanced mucormycosis. Concurrent management of the underlying pathology, monitoring of liver and kidney functions, and therapeutic drug monitoring are useful to ensure smooth and effective treatment.

MRI evaluation of Kimura's disease with emphasis on diffusion weighted imaging and enhancement characteristics

Kimura's disease is a rare disease of the head and neck region affecting mainly the adult males in eastern countries. The parotid and periparotid subcutaneous regions are the most common sites in head and neck region. Coupled with peripheral eosinophilia and raised serum IgE levels as characteristic features on hemogram, a painless swelling in parotid and periparotid region is diagnostic of Kimura's disease. Magnetic resonance imaging (MRI) has been an important modality in evaluating lesions of the head and neck region. Recently, interest in the diffusion weighted imaging (DWI) and contrast enhanced MRI (CEMRI) imaging of lesions in Kimura's disease has been noted to characterize it and differentiate it from other pathologies. We describe a case a recurrent Kimura's disease of the periparotid region and its MRI features with special emphasis on its characteristics on DWI and contrast enhanced sequences.

Methylmethacrylate Inter-Facetal and Inter-Vertebral Body Spacers for Cranio-Vertebral Junction and Various Spine Surgeries: Technical Note

STUDY DESIGN

Prospective.

PURPOSE

Over past one and half decade, ready-to-use magnetic resonance imaging (MRI) compatible spinal implants have changed the clinical practice and economics of spinal surgery. These are beyond reach of majority of population of developing countries like India due to financial reasons and also availability in remote areas. There is a growing need for a MRI compatible cost-effective spinal implant of proven quality. The authors used bone cement spacers for the said purpose for various level spine surgeries.

OVERVIEW OF LITERATURE

Methylmethacrylate, known as bone cement, was used extensively for spinal surgeries from craniovertebral junction to sacrum for augmentation and replacement of various spinal elements. Its biochemical and biomechanical properties were tested for safe clinical use and was a favored material for spinal surgeons.

MATERIALS AND METHODS

The authors made molds for making bone cement spacers for various spine levels with the help of silicone material.

RESULTS

Sixteen patients (12 males, 4 females with an average age of 31 years) of various spine level surgeries were done where bone cement spacers were used. It included patients of basilar invagination (n = 9), dorsal Pott's disease (n = 1), lumbar (n = 2), and lumbo-sacral spondylolisthesis (n = 1). Spacers could be used without any difficulties and postoperative day 1- and 3-months follow-up computed tomography scan of the patients revealed no change in the dimensions of the spacer and fusion at 3 months of operated levels.

CONCLUSION

The authors feel that bone cement spacers may be an effective and low-cost alternative to the existing costly alternatives.

Herlyn-Werner-Wunderlich (HWW) syndrome with kyphoscoliosis: a rare urogenital anomaly in a teenage girl

The obstructed haemivagina with ipsilateral renal agenesis (OHVIRA) syndrome also known as Herlyn-Werner-Wunderlich syndrome, a rare congenital malformation in females, results due to developmental abnormality in the müllerian duct. We are reporting a case of a 14-year-old girl who presented with pain and a lump in abdomen for the last 5 months. The MRI abdomen and pelvis confirmed the diagnosis of OHVIRA syndrome. The patient underwent haematocolpos and haematometra drainage, followed by vaginal septum resection.

Volume Rendering Technique (VRT) for Planning and Learning Cranio-Vertebral Junction (CVJ) Surgeries: Technical Note

CONTEXT

Volume rendering technique of Computed tomography scan is being used for surgical planning in cardio-thoracic, facio-maxillary, and orthopedics disciplines. Its application in CVJ surgeries has not been shown, so far.

METHODS

The authors used VRT images of CT scan in patients of congenital CVJ anomalies who were subjected to various surgeries through midline posterior approach. The screw entry points and courses of vertebral arteries were identified in relation to various landmarks on the VRT images, preoperatively and intra-operatively.

RESULTS

A total of 15 patients of CVJ anomalies, who underwent surgeries through midline posterior approach, formed the study group. The screw entry points and courses of the vertebral arteries could be effectively identified in the surgical fields.

CONCLUSION

We conclude that VRT images are an inexpensive and user friendly tool to identify the screw insertion points in the surgeries of CVJ anomalies. They also help in identifying the course of the vertebral artery in the surgical field. On the whole, their use makes the surgery in this region, safer.

Vanishing aneurysms in Behcet's disease - A case series

Behçet's disease is a systemic vasculitis with a wide spectrum of manifestations. Although pulmonary involvement is typical, the presence of pulmonary arterial aneurysms is associated with a high incidence of mortality and morbidity. We report two cases of Behçet's disease with pulmonary arterial involvement who presented with hemoptysis, showed significant treatment response, thus, highlighting the importance of early diagnosis and therapeutic management.

Temporal encephalocele into transverse sinus in an adult with partial seizures: MRI evaluation of a rare site of brain herniation

Herniation of brain parenchyma outside its normal enclosure (also known as encephalocele) has long been known to occur at certain classic sites and is classified accordingly. With widespread use of modern neuroimaging, the previously unknown atypical and rare sites of encephalocele have now been identified. Brain herniation into a dural venous sinus is one such recently described entity with case reports extending only upto the earlier part of this decade. With no definite clinical symptomatology, imaging is crucial to diagnose this lesion accurately and differentiate it from the more familiar entity in this region of the brain, the arachnoid granulations. Also known as occult encephalocele, focal brain herniation into dural venous sinus has few specific imaging features and characteristic sites. We report a case of a 21-year-old man with partial seizures in whom MRI of the brain revealed focal herniation of the normal temporal lobe parenchyma into the left transverse sinus and discuss the key imaging features and pathophysiology of this entity.

Bronchial Carcinoid Tumour as a Rare Cause of Cushing’s Syndrome in Children: A Case Report and Review of Literature

Cushing’s syndrome (CS) is rare in childhood and adolescence. The most common paediatric cause of CS is exogenous administration of glucocorticoids; either topical, inhaled or oral corticosteroids. Endogenous causes can be classified into adrenocorticotropic hormone (ACTH) independent and ACTH dependent causes. Herein, we report our experience of managing a 12 year old girl who presented with features of CS and was found to have an ectopic, ACTH-secreting bronchial carcinoid tumour, which was resected surgically. Our patient was managed successfully by multidisciplinary approach and has recovered from hypertension and Cushing’s habitus. The English language literature was searched from 2019 back, using PubMed, Google and Google Scholar. Keywords used for the search were; “Ectopic ACTH syndrome (EAS) in children”, “bronchial carcinoid in children” and “Cushing’s Syndrome in children”. Children with bronchial carcinoid tumours causing EAS were identified. Case variables such as age, sex, type of carcinoid, investigations, surgery, recurrences and outcome were reviewed. Fourteen cases of paediatric bronchial carcinoid producing ACTH were found with a mean age of 15.8 years and female preponderance. Most of the patients had a right lung lesion and histological appearance was typical of carcinoid tumour. Bronchial carcinoid is extremely rare in children and only 4% are associated with CS. The postoperative treatment of CS is challenging with a high prevalence of hypertension, increased body mass index and visceral fat mass, impaired cognitive function and decreased quality of life. A careful follow up is indispensable for monitoring recurrence of carcinoid and complete remission of CS.

Dural Ectasia of the Optic Nerve: A Rare Presentation in Neurofibromatosis Type I

Neurofibromatosis Type 1 (NF-1) is a common neurocutaneous syndrome with a characteristic spectrum of pathologies affecting the optic pathway. Optic pathway glioma and optic nerve meningioma are two such common afflictions of the optic nerve in NF-1. Dural ectasia of the optic nerve also known as optic nerve meningocele is a rare manifestation of optic nerve involvement in NF-1. Magnetic resonance imaging (MRI) is an excellent modality to accurately identify, characterize, delineate, and differentiate dural ectasia of the optic nerve from the commoner lesions such as optic glioma and meningioma in NF-1. We describe a case of a young woman with NF and a large recurrent palpebral neurofibroma. MRI evaluation of the orbits revealed extensive ectasia of the dura lining the cerebrospinal fluid sheath around all the segments of the optic nerve and around the optic chiasm.

Struma Ovarii: A Report of Three Cases and Literature Review

Struma ovarii is a variant of mature cystic teratoma, with predominant thyroid element. Confirmatory diagnosis is by histopathology. It may mimic as ovarian malignancy in some. It may be associated with ascites in minority; even CA-125 has been found to be raised in some cases. We here report three cases – two operated for suspected ovarian malignancy in a postmenopausal female and one case operated for persistent benign ovarian cyst with raised CA-125 in a young female. In all histopathological diagnosis was a benign struma ovarii. It is difficult to diagnose these cases preoperatively as there are no specific clinical, radiological or serum markers for these rare tumors in the absence of thyroid biology abnormality. Most cases are diagnosed on histopathology. These benign tumors many times require extensive staging laparotomy for suspected ovarian malignancy in the absence of preoperative diagnosis. Prognosis is good for these tumors. Subtle radiological signs and a clinical suspicion can avoid extensive staging laprotomies in these patients.

Pediatric pharmacovigilance in an institute of national importance: Journey has just begun

OBJECTIVE:

The objective of this study is to determine the nature and severity of adverse drug reactions (ADRs) in pediatric patients.

MATERIALS AND METHODS:

In this retrospective cohort study, we extracted the data from all the available pediatric ADR forms submitted to ADR monitoring center (AMC) from May 2014 to December 2016. The data including nature, frequency, causality (World Health Organization [WHO] causality scale), and the severity (Hartwig and Siegel scale for severity) of ADR were extracted. We also assessed the preventability of the event on modified Schumock and Thornton scale of ADR preventability.

RESULTS:

There were a total of 20 pediatric ADRs reported during this period. Nearly two-thirds of the ADRs occurred in patients who were receiving multiple drugs (polytherapy). Antimicrobial agents were the most commonly implicated drugs. The most common ADRs were skin rash (maculopapular, erythematous, and urticaria, itching, etc.). The severity and preventability scales indicated that most reactions (18/20) were moderate in nature and all were preventable. Four reactions were “certainly” and ten ADRs were “probably” related to the suspected drug as determined by the WHO causality assessment.

CONCLUSION:

Frequency of ADR increased with number of medications patient was receiving. Health-care providers (HCPs) involved in the care of children must be aware of this fact and should use additional drugs when absolutely necessary. They should be involved in pharmacovigilance program by exchanging and updating each other through sharing constructive information, communication, and education concerning the appropriate use of drugs in children. Pediatric pharmacovigilance is the need of the hour and should be given utmost importance for monitoring the safety of drugs in children. Motivating HCPs for voluntary reporting of ADRs for preventing the morbidity and mortality in this vulnerable population could be of immense importance.

Primary Management of Large Pancreatic Pseudoaneurysm by Ultrasound-Guided Percutaneous Thrombin Injection after Failure of Transarterial Pseudoaneurysm Embolization

Pancreatic pseudoaneurysm is a rare but life-threatening complication secondary to pancreatitis, surgery, trauma, or infection. Early treatment is advocated due to high risk of rupture and bleeding. Surgical treatment has traditionally been the first line but is associated with high morbidity. Transarterial embolization or exclusion is the treatment of choice; however, in cases with failure of endovascular treatment, percutaneous thrombin injection can be used successfully. We present a case of a large pancreatic pseudoaneurysm managed successfully with percutaneous ultrasound-guided thrombin injection after failure of transarterial management.

Short-term (48 hours) versus long-term (7 days) antibiotic prophylaxis for permanent pacemaker implantation

BACKGROUND

Infection following permanent pacemaker implantation is a dreaded complication. Antibiotic prophylaxis for 1-10 days at the time of implant has been used in the past but there is no consensus regarding its duration. We carried out a prospective, randomized study of two durations of antibiotic prophylaxis to determine which one was more effective.

METHODS AND RESULTS

One hundred and seventy-eight patients undergoing permanent pacemaker implantation for the first time were randomized to receive short duration (group A, n = 8 8) or longer duration (group B, n = 90) antibiotic prophylaxis for 2 days and 7 days, respectively. Patients in both groups received cloxacillin 2 g 2 hours prior to the procedure followed by ampicillin and cloxacillin (50 mg/kg/day in 4 divided doses) and gentamicin (3 mg/kg/day in 2 divided doses) for the respective duration. Patients were followed up for 1-17.3 months (9.3 +/- 1.8 months) in group A and 1-16.5 months (8.9 +/- 2 months) in group B. One patient in group B had an infection at the pacemaker site and two patients in each group had to undergo reimplantation due to pus in the pocket. There was no significant difference in the primary end-point in both groups.

CONCLUSIONS

A short course (48 hours) of antibiotic prophylaxis following permanent pacemaker implantation is as effective as a longer course (7 days).

Parathyroid hormone-related protein induces G1 phase growth arrest of vascular smooth muscle cells

In this study, we investigated the mechanisms responsible for the growth-inhibitory action of parathyroid hormone-related protein (PTHRP) in A10 vascular smooth muscle cells (VSMC). Fluorescence-activated cell sorting analysis of serum-stimulated VSMC treated with PTHRP or dibutyryl-cAMP (DBcAMP) demonstrated an enrichment of cells in G1 and a reduction in the S phase. Measurement of DNA synthesis in platelet-derived growth factor-stimulated VSMC treated with DBcAMP revealed that cells became refractory to growth inhibition by 12-16 h, consistent with blockade in mid-G1. cAMP treatment blunted the serum-induced rise in cyclin D1 during cell cycle progression without altering levels of the cyclin-dependent kinase cdk4 or cyclin E and its associated kinase, cdk2. Exposure of cells to PTHRP or cAMP resulted in a reduction in retinoblastoma gene product (Rb) phosphorylation. Immunoblotting of extracts from cAMP-treated cells with antibodies to cdk inhibitors revealed a striking increase in p27(kip1) abundance coincident with the G1 block. Immunoprecipitation with an anti-cyclin D1 antibody of cell lysates prepared from cAMP-treated cells followed by immunoblotting with antisera to p27(kip1) disclosed a threefold increase in p27(kip1) associated with cyclin D1 compared with lysates treated with serum alone. We conclude that PTHRP, by increasing intracellular cAMP, induces VSMC cycle arrest in mid-G1. This occurs secondary to a suppression in cyclin D1 and induction of p27(kip1) expression, which in turn inhibits Rb phosphorylation.