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J L Weissman

Publications and source records attributed to J L Weissman.

At least 19 recordsLinked to original sources
PubMed2026

Lifestyle Differentiation Among Marine Denitrifying Microorganisms.

Microorganisms carrying out denitrification in marine anoxic zones drive bioavailable nitrogen loss. Sequencing datasets have demonstrated the modularity of denitrification, with most populations having the genetic capability for only a subset of the pathway (NO3-➔NO2-➔NO➔N2O➔N2). Although previous work provided ecological explanations for this diversity among the functional modules, large trait variations exist within each functional module, and this within-module diversity and its biogeochemical implications remain unexplored. Here, we combine genomic data and modeling to explore how metabolic "lifestyle" strategies influence denitrifier community structure. We build a comprehensive genomic database of marine denitrifiers, and identify lifestyle differentiation among denitrifier functional groups. We then extend a mathematical ecosystem model by resolving two microbial functional types for each module representing a metabolic trade-off: a copiotroph, optimized for fast growth, and an oligotroph, optimized for high nutrient affinity. In the model, as the supply of organic matter relative to nitrate increases, the degree of copiotrophy among the community increases and then decreases. This suggests that oligotrophs are associated with either organic-matter- or nitrate-limiting conditions, whereas copiotrophic lifestyles are associated with an intermediate regime. Our model further associates NO2- reducers with oligotrophy and NO3- reducers with copiotrophy, particularly those producing greenhouse gas nitrous oxide (N2O), linking N2O production to substrate-replete conditions, which is consistent with our genome-based lifestyle estimates. Results provide insight into denitrifier ecological niches and thus the biogeochemical conditions that are associated with the production of intermediates, such as N2O, improving our understanding of how nitrogen cycling will change in a warming ocean.

Marine denitrifiers↗
PubMed2001

Hydroxyapatite: an alternative method of frontal sinus obliteration.

Obliteration of the frontal sinus may be necessary for the treatment of chronic sinusitis, infectious complications, trauma, and benign and malignant neoplasms. Hydroxyapatite cement (HAC) is a relatively new material that is approved for the repair of cranial defects. HAC has been successfully used to obliterate the frontal sinus in 19 patients with few minor complications and the avoidance of donor site morbidity. Compared with other alloplastic materials, HAC has the advantages of easy use, biocompatibility, and osseointegration.

Adolescent↗
PubMed2001

MRI detection of cervical metastasis from differentiated thyroid carcinoma.

BACKGROUND: With the advent of the use of serum thyroglobulin as a marker for the recurrence of well-differentiated thyroid cancer (WDTC) after total thyroidectomy, clinicians are increasingly faced with the diagnostic dilemma of detecting the site of recurrence in thyroglobulin-positive patients with normal clinical examinations. The high protein content of this thyroglobulin may make it specifically detectable by magnetic resonance (MR) imaging. OBJECTIVE: To determine the ability of MR imaging to detect the presence of metastatic WDTC in cervical lymph nodes. STUDY DESIGN: Retrospective cohort. METHODS: Blinded review by two independent head and neck radiologists of 34 head and neck MR scans obtained from 26 patients with thyroid cancer (12 with primary disease and 14 with recurrent disease) all of whom subsequently underwent surgical removal of the lymph nodes considered at risk by imaging. RESULTS: The average overall percent sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of MR imaging were 95%, 51%, 84%, 78%, and 83%, respectively. The concordance between the two radiologists was 69%. There was no overall difference in the ability of the MR scan to detect the presence of disease in the upper jugular, lower jugular, or paratracheal nodal stations. However, it was more useful for papillary carcinoma (PPV 86%, accuracy 85%) than for follicular carcinoma or the follicular variant of papillary carcinoma (PPV 63%, accuracy 67%). CONCLUSION: MR imaging is a sensitive and accurate technique for the detection of WDTC, particularly papillary carcinoma, metastatic to cervical lymph nodes. However, the lower specificity of this modality precludes its use as a screening tool.

Adenocarcinoma, Follicular↗
PubMed2001

"Puffed-cheek" CT improves evaluation of the oral cavity.

BACKGROUND AND PURPOSE: Maneuvers that distend a lumen facilitate radiographic examinations. In evaluation of the upper aerodigestive tract, Valsalva and phonation maneuvers complement barium fluoroscopy. The current work investigates "puffed-cheek" CT to improve visualization of oral cavity tumors. METHODS: Seven patients (ages 17 to 86 years) underwent conventional and puffed-cheek CT. Five had squamous cell carcinoma, one had benign verrucous hyperplasia of the buccal mucosa, one had "cheek swelling," and one had a pulsatile cheek mass. Conventional contrast-enhanced axial CT scans (3-mm thick, no interslice gap) were obtained through the oral cavity and neck. Each patient then pursed the lips and puffed out the cheeks, and axial images were obtained through the oral cavity (puffed-cheek scans). RESULTS: Three patients had normal conventional CT scans whereas puffed-cheek scans clearly showed the mass. Conventional CT in three patients showed a mass inseparable from two mucosal surfaces whereas puffed-cheek images clearly showed which surface the tumor involved. Two patients had normal conventional and puffed-cheek CT studies; in one, the physical examination was also normal. The other patient was a teenager with orthodontic appliances that created artifacts on both conventional and puffed-cheek images. Conventional angiography in this patient revealed a facial artery aneurysm. CONCLUSION: The puffed-cheek CT maneuver is easily taught, and patients comply readily. Puffed-cheek CT scans provide a clearer and more detailed evaluation of mucosal surfaces of the oral cavity than do conventional scans. In selected patients, the puffed-cheek technique can supplement conventional CT studies.

Adolescent↗
PubMed2000

Normal anatomy of the neck with CT and MR imaging correlation.

Knowledge of normal anatomy is the cornerstone for understanding pathologic processes. Often, the most difficult task for a radiologist is differentiating normal structures from pathology. There are many ways to organize a discussion of the normal anatomy in the neck. This article is organized by organ system, with an additional discussion of triangles, fascia, and spaces. Important normal variants are also discussed.

Fascia↗
PubMed2000

Imaging of tinnitus: a review.

Tinnitus, a buzzing or ringing in the ear, may be pulsatile or continuous (nonpulsatile). The distinction, with a detailed clinical evaluation, determines the most appropriate imaging study. Pulsatile tinnitus suggests a vascular neoplasm, vascular anomaly, or vascular malformation. Most of the neoplasms are glomus tympanicum and glomus jugulare tumors. Vascular anomalies may cause pulsatile tinnitus, but the mechanism is unknown, and another (treatable) cause should be sought. Most neoplasms and anomalies are best seen on bone algorithm computed tomographic (CT) studies. Dural vascular malformations are often elusive on all cross-sectional imaging studies; conventional angiography may be necessary to make this diagnosis. Flow-sensitive magnetic resonance (MR) images show vascular loops compressing the eighth cranial nerve. Carotid dissections, aneurysms, atherosclerosis, and fibromuscular dysplasia can be identified on both MR imaging or MR angiographic studies and CT or CT angiographic studies. Otosclerosis and Paget disease are CT diagnoses. Benign intracranial hypertension often has no abnormal imaging findings. For patients with nonpulsatile tinnitus, MR imaging is the study of choice to exclude a vestibular schwannoma or other neoplasm of the cerebellopontine angle cistern. Multiple sclerosis and a Chiari I malformation are rare causes of pulsatile tinnitus, also best seen on MR studies. Many patients with tinnitus have no abnormal imaging findings.

Algorithms↗
PubMed2000

The CT appearance of thyroglossal duct carcinoma.

BACKGROUND AND PURPOSE: Thyroid carcinoma arising in a thyroglossal duct cyst may be clinically indistinguishable from a benign thyroglossal duct cyst. The preoperative diagnosis of carcinoma, however, can have important implications for surgical planning and postoperative treatment. Our purpose was to describe the CT appearance of thyroglossal duct carcinoma and identify the features that distinguish thyroglossal duct carcinoma from benign thyroglossal duct cysts. METHODS: Retrospective review of the medical records from the University of Pittsburgh Medical Center and Geisinger Medical Center (Danville, Pennsylvania) identified six patients with papillary thyroid carcinoma within the thyroglossal duct who had undergone preoperative CT examinations of the neck. There were two women and four men. Their ages ranged from 14 to 59 years. Three patients underwent contrast-enhanced CT of the neck, and three underwent unenhanced CT. All CT examinations consisted of 3- to 5-mm-thick contiguous axial sections. RESULTS: Each patient had an anterior neck mass with a cystic component. Two of the masses had dense or enhancing mural nodules, two had irregular calcification throughout the mass, and two had dense or enhancing mural nodules with additional foci of calcification. One patient had cervical lymphadenopathy. CONCLUSION: Carcinoma should be considered in thyroglossal duct cysts that have a mural nodule or calcification or both.

Adolescent↗
PubMed2000

Traumatic neuroma after neck dissection: CT characteristics in four cases.

BACKGROUND AND PURPOSE: Traumatic neuroma, an attempt by an injured nerve to regenerate, may present as a palpable nodule or an area sensitive to touch (trigger point) after neck dissection. The purpose of this study was to identify CT characteristics of traumatic neuroma in four patients after neck dissection. METHODS: Between April 1995 and November 1998, the CT studies in three men and one woman (ages, 45-64 years) who had had a radical neck dissection and a nodule posterior to the carotid artery were reviewed retrospectively. CT was performed 1.5 to 6 years after neck dissection with clinical correlation and/or pathologic examination. Three patients had squamous cell carcinoma of the upper aerodigestive tract and one had a primary parotid adenocarcinoma. RESULTS: Three patients with a traumatic neuroma had a centrally radiolucent nodule with peripherally dense rim and intact layer of overlying fat, which was stable on CT studies for 1 to 2 years. One of these had a clinical trigger point. The fourth patient with a pathologically proved traumatic neuroma mixed with tumor had intact overlying fat, but the nodule lacked a radiolucent center and was not close to the carotid artery. CONCLUSION: The CT findings of a stable nodule that is posterior but close to the carotid artery with central radiolucency, a dense rim, and intact overlying fat, combined with the clinical features of a trigger point and a lack of interval growth, strongly suggest the diagnosis of traumatic neuroma.

Carotid Arteries↗
PubMed1999

MR imaging of intraventricular silicone: case report.

A 42-year-old man with human immunodeficiency viral infection developed cytomegaloviral retinitis that was complicated by retinal detachment and was treated with an intravitreous injection of silicone. Fifteen months later, magnetic resonance imaging revealed intraocular and intraventricular silicone. Signal intensity characteristics and chemical shifts of silicone in the two locations were identical.

AIDS-Related Opportunistic Infections↗
PubMed1999

Imaging of a Stafne bone cavity: what MR adds and why a new name is needed.

Stafne bone cavities are asymptomatic radiolucencies seen at the angle of the mandible. Although plain films are often sufficient for diagnosis, confirmatory imaging is needed in atypical cases. We describe the MR imaging findings of a Stafne bone cavity, describe the contents, explain why a new name is needed, and discuss the relative merits of different radiologic techniques for establishing this diagnosis.

Alveolar Process↗
PubMed1999

Current imaging techniques for head and neck tumors.

Modern head and neck imaging has led to advances in both the diagnosis and treatment of head and neck cancers. Both computed tomography (CT) and magnetic resonance imaging (MRI) studies provide important information about the location and extent of neoplasm, particularly with respect to the interface of tumor with bone, fat, muscles and other soft tissues, air, blood vessels, dura, and brain. Conventional angiography can be used to assess tumor blood supply and vascularity and to perform therapeutic embolization. Magnetic resonance angiography (MRA) and CT angiography (CTA) are new tools for the noninvasive evaluation of blood vessels. Positron emission tomography (PET) shows promise for differentiating tumor from scar, edema, and other nonneoplastic soft tissues.

Diagnostic Imaging↗
PubMed1998

Intranasal endoscopic excision of a juvenile angiofibroma.

Intranasal endoscopic excision of a juvenile nasopharyngeal angiofibroma (JNA) was performed in a 13 year old white male. The patient remains disease-free 24 months after the operation. Although endoscopic surgical techniques have been applied to the therapy of some benign nasal tumors, such as inverting papilloma, endoscopic resection of a documented JNA has not been previously reported. This technique is reserved for tumors which are limited to the nasal cavity and paranasal sinuses with minimal extension into the pterygopalatine fossa.

Adolescent↗
PubMed1998

Thyroid gland after total laryngectomy: CT appearance.

PURPOSE: To determine the computed tomographic (CT) appearance of the normal thyroid gland after total laryngectomy, because the high attenuation (or heterogeneous attenuation) of thyroid parenchyma was misinterpreted as tumor on several CT studies. MATERIALS AND METHODS: A search of computerized clinical files compiled from January 1996 through August 1997 yielded data on 24 patients who had undergone laryngectomy and subsequent CT of the neck. From these 24 patients, CT findings were available in 21. Because one patient had undergone total thyroidectomy and was excluded from the study, a retrospective review was performed in the remaining 20 patients. RESULTS: In 14 patients, unilateral thyroid tissue was present; in the other six there was bilateral thyroid tissue not connected by an isthmus. Thus, there were 26 remaining thyroid lobes, of which six were round and 20 were oval or lobular. Nineteen lobes showed homogeneously high attenuation (including one scanned without use of contrast material), six showed heterogeneous high attenuation or contained areas of hyperlucency, and one was obscured by streak artifact. CONCLUSION: Thyroid tissue can appear as unilateral or bilateral asymmetric masses on neck CT scans after laryngectomy. Gland tissue can show homogeneously or heterogeneously high attenuation. Familiarity with the varied postoperative appearance of normal thyroid gland can prevent its misdiagnosis as tumor.

Adult↗
PubMed1998

Anterior facial vein and submandibular gland together: predicting the histology of submandibular masses with CT or MR imaging.

PURPOSE: To test the hypothesis that the relationship of the anterior facial vein to the submandibular salivary gland and a mass in the submandibular fossa could help identify the origin of the mass at computed tomography (CT) or magnetic resonance (MR) imaging. MATERIALS AND METHODS: Thirteen patients with 14 palpable submandibular masses, surgical and histologic confirmation, and contrast material-enhanced CT images (12 patients) or MR images (one patient) that showed the anterior facial vein were identified with review of files from 1985 to 1997. Six patients had submandibular gland disease: three with primary neoplasms, two with metastatic tumor invading the gland, and one with chronic sialoadenitis. Eight patients had masses arising outside the gland (seven with lymphadenopathy, one with a plexiform neurofibroma). RESULTS: The anterior facial vein did not separate primary tumors, tumors invading the gland, or lobulations of the enlarged gland from the body of the gland. The vein was identified between enlarged lymph nodes and the gland. The vein did not separate the gland from the neurofibroma, but this tumor was medial to the gland; the vein runs lateral to the gland. CONCLUSION: The anterior facial vein is a useful landmark in determining the origin of a submandibular mass. Primary disease of the gland is never separated from the gland by the vein. The vein does separate lymphadenopathy from the gland and, theoretically, separates the gland from soft-tissue tumors lateral to the gland.

Adult↗
PubMed1998

Imaging of Bezold's abscess.

OBJECTIVE: Our purpose was to describe the CT findings in patients with Bezold's abscesses. CONCLUSION: Bezold's abscesses are rare complications of mastoiditis. In our series most were seen in adults and were associated with a history of cholesteatoma and mastoidectomy. CT of the neck and temporal bone can help the surgeon determine appropriate treatment.

Abscess↗
PubMed1998

Beyond the promontory: the multifocal origin of glomus tympanicum tumors.

PURPOSE: We examined other middle ear locations of glomus tympanicum tumors, which arise from glomus bodies accompanying the tympanic (Jacobson's) nerve through the middle ear. Most descriptions place these tumors on the promontory over the basal turn of the cochlea. METHODS: We identified seven patients (all women) with small surgically confirmed glomus tympanicum tumors (not completely filling the middle ear) for whom CT scans were available for retrospective review. Patients' ages ranged from 23 to 78 years at the time of the high-resolution CT study (1.0- to 1.5-mm-thick sections). RESULTS: All tumors arose on the medial wall of the middle ear. One was anterior to the promontory, beneath the cochleariform process and the semicanal of the tensor tympani. Two were inferior to the promontory, in the recess beneath the basal turn of the cochlea. Four were anteroinferior. None was actually on the apex of the promontory. CONCLUSION: Glomus tympanicum tumors may arise in various locations on the medial wall of the middle ear, where Jacobson's nerve runs. The promontory is only one middle ear location in which glomus tympanicum tumors may arise. Familiarity with the course of the tympanic nerve helps tailor the search for, and facilitates accurate identification of, tiny glomus tympanicum tumors.

Adult↗