Double-line Sign Research Articles

Identification of Mitral Valve Prolapse on Non-electrocardiography-gated Enhanced Chest Computed Tomography.

The primary imaging modality for the diagnosis of mitral valve prolapse (MVP) is echocardiography supplemented by electrocardiography (ECG)-gated cardiac computed tomography (CT) angiography. However, we have recently encountered patients with MVP who were initially identified on non-ECG-gated enhanced chest CT. The purpose of this study is to evaluate the diagnostic accuracy of non-ECG-gated enhanced chest CT to predict the presence of MVP. Of 92 patients (surgically confirmed MVP who underwent non-ECG-gated chest CT), 27 patients were excluded for motion artifact or insufficient surgical correlation, and 65 patients were ultimately included. As a control, 65 patients with dyspnea and without MVP (non-ECG-gated chest CT and echocardiography were performed within 1 month) were randomly selected. We retrospectively analyzed an asymmetric double line sign on axial CT images for the presence of MVP. The asymmetric double line sign was defined as the presence of a linear structure, not located in the plane traversing the mitral annulus. Use of the asymmetric double line sign to predict MVP on non-ECG-gated CT showed modest sensitivity, high specificity, modest negative predictive value, and high positive predictive value of 59% (38/65), 99% (64/65), 70% (64/91), and 97% (38/39), respectively. The asymmetric double line sign on non-ECG-gated enhanced chest CT may be a valuable finding to predict the presence of MVP. Familiarity with this CT finding may lead to prompt diagnosis and proper management of MVP.

Multifocal Osteonecrosis in the Foot and Ankle After Extracorporeal Membrane Oxygenation: A Case Report.

Osteonecrosis is acknowledged as a relatively uncommon disorder caused by various factors, including autoimmune diseases, drug-induced diseases, inherited metabolic disorders, coagulation disorders, and underlying malignancies. To our knowledge, no previous research has investigated osteonecrosis stemming from extracorporeal membrane oxygenation. Herein, we report a rare case of postperipheral venoarterial extracorporeal membrane oxygenation-induced multifocal osteonecrosis in the foot and ankle that demonstrated a low serpiginous peripheral signal on T1-weighted images and a double-line sign on fat-suppressed or T2-weighted magnetic resonance images. Conservative treatment was applied, and the patient was mostly recuperated after 6 months.

DISEASE BURDEN OF AVASCULAR NECROSIS OF FEMORAL HEAD IN NON-TRAUMATIC HIP PAIN WITH REVIEW OF LITERATURE

Objective: Avascular Necrosis happens to be one of the most common diseases in patients presenting with a chronic painful hip. We have evaluated these patients in the background of demographic details. Material and Method: Prospective study evaluating 319 patients using conventional X-ray and MRI. Imaging findings were evaluated and staging of AVN was done on both modalities. Demographic details were documented in the background of clinical settings. Results: 10.6% of the cases were diagnosed on X-Ray (34 patients). Sequential MRI examination picked up 21% MRI (68 patients). X-ray was missing the diagnosis of AVN in nearly 50% of the cases. 46% of the cases (147 patients) were from age groups ranging from 20-40 years, followed by older patients. It is comparatively rare in young, and if present is associated with other systemic diseases. 60% of the patients were male and 40% of the patients were females. Bilateral hip pain was present in 31% of the cases (100 patients). Right side involvement (37%) was slightly more common than left (32%) in cases with unilateral hip pain. Commonly encountered imaging findings associated were femoral head marrow oedema in 59 patients (87%), double-line sign in 54 patients (79%), subchondral cysts in 42 patients (62%), followed by joint effusion, joint space reduction, femoral head altered contour, femoral head fragmentation with collapse. Conclusion: X-ray alone can miss up to 50% of the cases of Avascular Necrosis of the femoral head, especially in milder and potentially salvageable cases. Correct imaging interpretation and grading make the role of MRI pivotal.

EFAST exam errors at a level 1 trauma center: A retrospective cohort study.

Extended Focused Assessment with Sonography for Trauma (eFAST) ultrasound exams are central to the care of the unstable trauma patient. We examined six years of eFAST quality assurance data to identify the most common reasons for false positive and false negative eFAST exams. This was an observational, retrospective cohort study of trauma activation patients evaluated in an urban, academic Level 1 trauma center. All eFAST exams that were identified as false positive or false negative exams compared with computed tomography (CT) imaging were included. 4860 eFAST exams were performed on trauma patients. 1450 (29.8%) were undocumented, technically limited, or incomplete (missing images). Of the 3410 remaining exams, 180 (5.27%) were true positive and 3128 (91.7%) were true negative. 27 (0.79%) exams were identified as false positive and 75 (2.19%) were identified as false negative. Of the false positive scans, 7 had no CT scan and 8 had correct real-time trauma paper documentation of eFAST exam results when compared to CT and were excluded, leaving 12 false positive scans. Of the false negative scans, 11 were excluded for concordant documentation in real-time trauma room paper documentation, 20 were excluded for no CT scan, and 2 were excluded as incomplete, leaving 42 false negative scans. Pelvic fluid, double-line sign, pericardial fat pad, and the thoracic portion of the eFAST exam were the most common source of errors. The eFAST exams in trauma activation patients are highly accurate. Unfortunately poor documentation and technically limited/incomplete studies represent 29.8% of our eFAST exams. Pelvic fluid, double-line sign, pericardial fat pad, and the thoracic portion of the eFAST exam are the most common source of errors.

Development and validation of a magnetic resonance imaging-based nomogram for predicting invasive forms of placental accreta spectrum disorders.

The aim of the study was to develop and validate a magnetic resonance imaging (MRI)-based nomogram for predicting invasive forms of placental accreta spectrum (PAS) disorders (placenta increta and percreta) with "uncertain ultrasound diagnosis." This was a retrospective cohort study of a primary cohort of 118 patients and a validation cohort of 65 patients with "uncertain ultrasound diagnosis," who were further evaluated by MRI. MRI signs associated with PAS disorders were analyzed between invasive and noninvasive groups by both univariate and logistic regression to construct the nomogram. The accuracy and discriminative ability of the nomogram were measured by concordance index (C-index) and calibration curve internally and externally. The history of previous cesarean deliveries (odds ratio [OR], 3.27; 95% confidence interval [CI], 1.16-9.27), loss of double-line sign (OR, 9.49; 95% CI, 3.06-29.48), abnormal uterine bulging (OR, 4.05; 95% CI, 1.53-10.69), and disorganized abnormal placenta vascularity (OR, 3.38; 95% CI, 1.09-10.50) were imputed for the nomogram. The C-index of the nomogram was 0.85 for internal validation and 0.84 for external validation. Calibration curve showed good agreement with predicted risk and actual observation for both primary and validation cohort. MRI can be a useful adjunct for clinical staging of patients with "uncertain ultrasound diagnosis."

The Double Line Sign: Thinking about a Bone Infarction

The Double Line Sign: Thinking about a Bone Infarction

Radiological evaluation of avascular necrosis of bone with clinical correlation

Osteonecrosis of bone is a progressive disease affecting the areas with precarious blood supply like head of the femur, head of the humerus, Scaphoid, Talus, Navicular, Condyles of long bones etc. Causes are mostly unknown and few are related to Corticosteroids, Trauma, Alcoholism, and hematological disorders. In the present study, 45 symptomatic patients were evaluated for osteonecrosis using X Ray, CT Scan and MRI in a tertiary care hospital. The age of incidence, gender variability, laterality, involvement of the different bones were studied. The sensitivity of various imaging modalities according to the disease stages was also noted. In majority of the cases the cause was unknown and the head of the femur came out to be the most involved site. MRI was found to be the most sensitive imaging modality followed by CT and X ray. The common findings detected by X ray and CT were Sclerosis, Subchondral lucency, Altered morphology and associated degenerative changes. Bone marrow edema was the most common finding detected by MRI in very early stage. Joint effusion, Double line sign, subchondral collapse, degenerative changes of the joint were other significant findings. T1 hyposensitivity was the main finding in the osteonecrosis of Scaphoid, Navicular and Talus with no enhancement post contrast.

Osteochondral Lesions of the Knee: Differentiating the Most Common Entities at MRI.

Several pathologic conditions may manifest as an osteochondral lesion of the knee that consists of a localized abnormality involving subchondral marrow, subchondral bone, and articular cartilage. Although understanding of these conditions has evolved substantially with the use of high-spatial-resolution MRI and histologic correlation, it is impeded by inconsistent terminology and ambiguous abbreviations. Common entities include acute traumatic osteochondral injuries, subchondral insufficiency fracture, so-called spontaneous osteonecrosis of the knee, avascular necrosis, osteochondritis dissecans, and localized osteochondral abnormalities in osteoarthritis. Patient demographics, the clinical presentation, and the role of trauma are critical for differential diagnosis. A localized osteochondral defect can be created acutely or can develop as an end result of several chronic conditions. MRI features that aid in diagnosis include the location and extent of bone marrow edema, the presence of a fracture line, a hypointense area immediately subjacent to the subchondral bone plate, and deformity of the subchondral bone plate. These findings are essential in diagnosis of acute traumatic injuries, subchondral insufficiency fracture, and its potentially irreversible form, spontaneous osteonecrosis of the knee. If the lesion consists of a subchondral region demarcated from the surrounding bone, the demarcation should be examined for completeness and the presence of a "double-line sign" that is seen in avascular necrosis or findings of instability, which are important for proper evaluation of osteochondritis dissecans. Subchondral bone plate collapse, demonstrated by the presence of a depression or a fluid-filled cleft, can be seen in advanced stages of both avascular necrosis and subchondral insufficiency fracture, indicating irreversibility. Once the diagnosis is established, it is important to report pertinent MRI findings that may guide treatment of each condition. ©RSNA, 2018 An earlier incorrect version of this article appeared online. This article was corrected on August 23, 2018.

The differential diagnosis value of high frequency ultrasound in dorsal thyroid nodules

Objective To explore the value of high frequency ultrasound in differential diagnosis in dorsal thyroid(including gland dorsal or posterior) nodules. Methods Ultrasonographic features of 101 patients with ultrasonography suspected or misdiagnosed nodules in the dorsal area of the thyroid gland, which were then confirmed by pathology or hyaluronography/gastroscopy, were retrospectively analyzed. Ultrasonographic homogeneity (other nodules with similar ultrasonographic features were found in the ipsilateral gland), parenchyma homology (nodule parenchyma was continuous with glandular parenchyma) and blood homology (blood flow signals in nodules were continuous with those in glandular parenchyma) were applied as indicators for determinng thyroid nodules. Double-line sign or vascular arch sign at the edge of nodules served as an indicator for determining parathyroid nodules. Results Of the 101 cases, there were 46 thyroid nodules, 35 parathyroid nodules, 7 enlarged lymph nodes; 6 esophageal diverticulum, 6 esophageal cancer, 1 cleft cyst.The determination of thyroid nodules by at least one of ultrasonographic homogeneity, parenchyma homology and blood homology showed sensitivity of 73.5%, specificity of 96.5% and accuracy of 85.8%. In the determination of parathyroid nodules by double-line sign or vascular arch sign at the edge of nodules, sensitivity, specificity and accuracy was 54.1%, 85.5% and 74.5%, respectively. Conclusions Nodules in the dorsal area of the thyroid gland have different sources, and the understanding of corresponding characteristic ultrasonographic appearances is helpful for improving the differential diagnosis of these nodules. Key words: Ultrasonography; Thyroid nodule; Parathyroid diseases

Multifocal Osteonecrosis in Systemic Lupus Erythematosus

Clinical Image: A 55 years old African male known case of SLE, Hypertension and atrial fibrillation was admitted in Internal medicine unit with acute ischemic stroke. He was on 10 mg prednisolone, azathioprine 50 mg BD and hydroxychloroquine 200 mg once daily and was in remission. His last SLE flare was 6 months back. On day 3, he complained of left knee pain. Left knee and lower thigh were tender without any swelling or erythema. Radiographs of left knee joint showed serpiginous sclerosis (A) along the distal femur and proximal tibia suggestive of bone infarcts. No periosteal reaction was detected and joint space was preserved. MRI lower limbs showed bilateral involvement of distal femur and proximal tibia with intramedullary lesion (B) having serpiginous borders and characteristic double line sign consisting of high signal intensity inside and a low intensity peripheral rim (C ) on T2WI /STIR and TIWI (D) (Figure 1). His pain was controlled with simple analgesics (NSAIDs, acetaminophen). He was pain free on follow up visit in 4 weeks.

Prevalence of the "double-line" sign when performing focused assessment with sonography in trauma (FAST) examinations.

The double-line sign (DLS) is a wedge-shaped hypoechoic area in Morison's pouch bounded on both sides by echogenic lines. It represents a false-positive finding for free intraperitoneal fluid when performing focused assessment with sonography in trauma examinations. The purpose of this study was to determine the prevalence of DLS. Secondarily, the study will further investigate the relationship between the presence of a DLS and body mass index (BMI). This was a prospective study that enrolled patients over a 7-month period. Inclusion criteria were patients ≥ 18 years of age presenting to the Emergency Department (ED) requiring a FAST examination as part of the patient's standard medical care. Each examination was performed by one of six experienced ultrasonographers. Presence or absence of the DLS was established in real time and gender, height, weight, and BMI were recorded for each patient. The overall prevalence rate of DLS and the corresponding 95 % confidence interval were calculated, as well as the prevalence rates broken down by BMI characterized as underweight, normal weight, overweight, and obese; and age category (18-29, 30-64, and 65+). The Chi-square test and a Fisher's exact test for BMI category were used to compare the prevalence rates of positive DLS among the different demographic groups. 100 patients were enrolled in the study; the overall prevalence was 27 %. There was no statistical significance among the different demographic groups or BMI. The DLS is a prevalent finding. We believe this sign has become more apparent due to improved imaging technology and resolution.

Important Signs in Musculoskeletal MRI

The purpose of this article is to review the common MRI signs of musculoskeletal pathology. In this article, 15 classic MRI signs used in musculoskeletal radiology are presented and described. These signs incl ude the anterior drawer sign, bone bruise sign, bow tie sign, celery stalk anterior cruciate ligament (ACL), cyclops lesion, deep lateral femoral notch sign, double line sign, double Oreo cookie sign, double posterior cruciate ligament (PCL) sign, fat - bloo d interface (FBI) sign, fragment in notch sign, split fat sign, T - sign, target sign, and yo - yo on a string sign. It is important to recognize common signs in musculoskeletal MRI and understand the underlying pathologies for accurate image interpretation.

Rapid magnetic resonance imaging protocol for detecting femoral head avascular necrosis: A case series-it′s utility in the general population in developing countries

Introduction: Osteonecrosis of the femoral head is an increasing cause of musculoskeletal disability, common among the younger population, between the third and fifth decade of life, affecting mainly men, thereby requiring prompt diagnosis and early intervention. Aims and Objectives: The aim was to formulate a limited magnetic resonance imaging (MRI) examination protocol for detection of avascular necrosis (AVN) in clinically suspected cases that can be performed rapidly and will be inexpensive. Materials and Methods: Forty-five patients suspected clinically and or on conventional radiography for AVN of the femoral head were referred for MRI hip. MRI hip was done on 1.5 T Siemens Avanto. Of 45, 36 were detected to have AVN (total 58 hips), whereas 9 did not have AVN on MRI. Initially, coronal T1-weighted image (T1WI) sequence was obtained as limited MRI protocol, followed by complete MRI examination. Results: Maximum patients belonged to age group 31-40 (30.5%). 32 (88.88%) patients were males and 4 (11.11%) were females. Bilateral AVN was detected in 44 (61.1%) and unilateral in 14 patients (38.8%). Pre collapsed stage (Stages I and II) was detected in 18 hips (31.03%), collapsed stage (Stages III and IV) was detected in 40 hips (68.9%). Peripheral low-intensity rim was seen on T1WI in all 58 cases of AVN. Double line sign on T2-weighted image was seen in 33/58 (56.8%). Conclusion: Our study concluded that coronal T1W sequence is an easy, rapid and cost-effective method of detecting unilateral or bilateral AVN.

From the radiologic pathology archives imaging of osteonecrosis: radiologic-pathologic correlation.

Osteonecrosis is common and represents loss of blood supply to a region of bone. Common sites affected include the femoral head, humeral head, knee, femoral/tibial metadiaphysis, scaphoid, lunate, and talus. Symptomatic femoral head osteonecrosis accounts for 10,000-20,000 new cases annually in the United States. In contradistinction, metadiaphyseal osteonecrosis is often occult and asymptomatic. There are numerous causes of osteonecrosis most commonly related to trauma, corticosteroids, and idiopathic. Imaging of osteonecrosis is frequently diagnostic with a serpentine rim of sclerosis on radiographs, photopenia in early disease at bone scintigraphy, and maintained yellow marrow at MR imaging with a serpentine rim of high signal intensity (double-line sign) on images obtained with long repetition time sequences. These radiologic features correspond to the underlying pathology of osseous response to wall off the osteonecrotic process and attempts at repair with vascularized granulation tissue at the reactive interface. The long-term clinical importance of epiphyseal osteonecrosis is almost exclusively based on the likelihood of overlying articular collapse. MR imaging is generally considered the most sensitive and specific imaging modality both for early diagnosis and identifying features that increase the possibility of this complication. Treatment subsequent to articular collapse and development of secondary osteoarthritis typically requires reconstructive surgery. Malignant transformation of osteonecrosis is rare and almost exclusively associated with metadiaphyseal lesions. Imaging features of this dire sequela include aggressive bone destruction about the lesion margin, cortical involvement, and an associated soft-tissue mass. Recognizing the appearance of osteonecrosis, which reflects the underlying pathology, improves radiologic assessment and is important to guide optimal patient management.

Autologous Adipose Tissue-Derived Stem Cells Induce Persistent Bone-Like Tissue in Osteonecrotic Femoral Heads

Background: Osteonecrosis, also known as avascular necrosis, of the femoral head is a debilitating disorder that commonly affects 30- to 50-year-old individuals. Currently, definitive treatment is limited to total hip replacement. However, recent studies have demonstrated bone regeneration in the femoral head after the infusion of bone marrow-derived mesenchymal stem cells. In addition, local injection of adipose tissue-derived stem cells has been shown to regenerate medullary bonelike tissue 3 months after treatment. However, there have been no long-term follow-up studies on humans treated with adipose tissue-derived stem cells for osteonecrosis. Objectives: To determine if treatment with adipose tissue-derived stem cells and platelet-rich plasma leads to the regeneration of medullary bone-like tissue and long-term reduction of hip pain in patients with femoral head osteonecrosis. Methods: This report of two clinical cases was in compliance with the Declaration of Helsinki. Also, the Korean Food and Drug Administration has allowed the use of adipose tissue-derived stem cells (ADSCs) in medical treatments since 2009. To obtain ADSCs, lipoaspirates were obtained from lower abdominal subcutaneous adipose tissue. The stromal vascular fraction was separated from the lipoaspirates by centrifugation after treatment with collagenase. The stem-cell-containing stromal vascular fraction was mixed with calcium chloride-activated platelet rich plasma and hyaluronic acid, and this mixture was then injected into the diseased hip. The affected hip was reinjected with calcium chloride-activated platelet rich plasma weekly for 4 weeks. Patients were subjected to preand post-treatment magnetic resonance imaging (MRI) scans. Results: Two patients (34- and 39-year-old men) with femoral head osteonecrosis and severe hip pain were treated with adipose-derived stem cells. The MRI scans of the affected hip in both patients showed segmental areas of low signal intensity (T1 axial views) in the subchondral bones with a “double line sign” consistent with osteonecrosis. The visual analog scale score, physical therapy testing, and Harris Hip score of both patients improved after stem cell treatment. Both patients also demonstrated post-procedure improvement in their MRI scans, evidenced by positive T1 signal changes consistent with medullary bone regeneration. Further, the long-term reduction in hip pain was correlated with the MRI findings indicative of bone regeneration. Limitations: A biopsy of the regenerated tissue was not conducted in either patient. Thus, the true nature of the treatment-induced changes is unknown. Further, the MRI results may contain artifacts due to the difficulty in capturing the exact treatment location. It can only be speculated that there was neovascularization to support the newly regenerated medullary bone-like tissue. Conclusion: These 2 cases demonstrate the presence of sustained, regenerated medullary bonelike tissue in 2 severely necrotic femoral heads and suggest that this rather simple, minimally invasive percutaneous procedure may hold great promise as a therapy for patients with femoral head osteonecrosis. Key words: Femoral head osteonecrosis, avascular necrosis, bone necrosis, cell-based treatment, bone regeneration, hip pain, adipose tissue-derived stem cells, ADSC.

Bone Apposition of the Acetabular Rim in Deep Hips

Hips with coxa profunda can develop a pincer-type impingement with linear impact between the proximal part of the femur and the acetabulum, leading to bone apposition on the acetabular rim. Twenty hips with radiographic features of rim ossification were isolated from a pilot cohort of 220 patients for histologic assessment of the acetabular rim and the labrum. In the second part of the study, the prevalence of radiographic signs of bone apposition in a cohort of 148 hips treated for femoroacetabular impingement was assessed. Histologic analysis confirmed that the labrum may become displaced and replaced by the appositional bone formation. The double-line sign and the recess sign are suggestive of an ongoing process of this bone formation, and the described phenotypes of bone apposition indicate the site of the impingement problem. Morphological anomalies of the proximal part of the femur, such as a low neck-shaft angle or a short femoral neck, may further contribute to the mechanism of pincer impingement. In later stages, this bone formation cannot be distinguished from the native bone and the labrum may appear to be nearly absent on imaging studies. While the bone apposition on the rim is first reactive to chronic impingement, the impingement then increases and may lead to further bone apposition.

Osteonecrosis Mimicking Bone Metastasis in Femoral Head on (18)F-FDG PET/CT: A Case Report.

A 77-year-old woman underwent chemotherapy, radiotherapy, and brachytherapy for cervical cancer 9 years ago. On a follow-up (18)F-fluorodeoxyglucose (FDG) PET/CT image, focal FDG uptake was noted in a focal osteolytic lesion in the right femoral head. During magnetic resonance imaging, this lesion showed subchondral dark-signal-intensity rim on T1-weighted image and double line sign on T2-weighted image, suggestive of osteonecrosis. The lesion was pathologically confirmed as osteonecrosis after surgery. This case demonstrates that osteonecrosis of the femoral head may demonstrate focal FDG uptake mimicking bone metastasis.

IMAGING DIAGNOSIS-MEDULLARY TIBIAL INFARCTION IN A HORSE

An Andalusian Stallion with left hind limb lameness had a radiolucent lesion in the medullary cavity of distal tibial metaphysis. After euthanasia for other disease, the tibia was examined with magnetic resonance (MR). The MR imaging sequences were characterized by a double line sign, although showing quite different lesion area intensities. Histologically, the lesion was compatible with medullary infarction being characterized by normal spongy bone, areas of abundant fibrous tissue and numerous necrotic adipocytes in various stages of destruction.

Osteonecrosis of the Tibial Plateau

To determine the magnetic resonance (MR) imaging appearances of osteonecrosis of the tibial plateau and perform quantitative analysis of the extent of the necrotic area. Twenty-eight patients (34 knees) with osteonecrosis were retrospectively evaluated using MR imaging and other modalities where available. A computerized image analysis program that allowed quantification of the lesion size was used to obtain measurements of the extent of involvement, which were then incorporated into each stage of the disease. The MR imaging findings of osteonecrosis of the tibial plateau included subchondral regions of abnormal signal intensity (n = 28), a double-line sign (n = 11), and fractures (n = 9). Meniscal tears and cartilage abnormalities were disclosed in the affected knee compartment with an equal frequency (n = 17). The size of the necrotic lesion varied among different stages of the disease as follows: 6.8% to 15.7% (stage I); 6.5% to 59.3% (stage II); 23.5% to 61.3% (stage III); and 34.3% to 75% (stage IV). The extent of involvement was greater in stage II than that in stage I (P < 0.001) and in stage IV than that in stage III (P < 0.05), whereas the extent of involvement in stage III was not significantly greater than that in stage II (P > 0.05). The MR imaging characteristics of osteonecrosis of the tibial plateau are variable. The association of osteonecrosis at this site with meniscal tears and cartilage abnormalities has important implications for pathogenesis of the disease as it relates to physical stress. Quantification of the lesion size provides precise information for optimal staging of the disease.

The Double-Line Sign: A False Positive Finding on the Focused Assessment with Sonography for Trauma (FAST) Examination

Emergency physicians commonly perform Focused Assessment with Sonography for Trauma (FAST) examinations to evaluate for free intraperitoneal fluid. Many ultrasound findings can be misinterpreted as free fluid, resulting in false-positive FAST examinations. To describe a previously unreported ultrasound finding that can be misinterpreted as free intraperitoneal fluid. A 32-year-old man was stabbed in the left upper abdomen. A FAST examination was performed and a right perinephric fat pad was interpreted as showing free fluid in Morison's pouch. After transfer to a trauma center, a repeat FAST examination revealed no signs of intraperitoneal free fluid. Wound exploration showed no signs of penetration into the peritoneal cavity. When performing a FAST examination, a wedge-shaped hypoechoic area in Morison's pouch that is bounded on both sides by echogenic lines (the "FAST Double-Line Sign") is likely to represent perinephric fat and may result in a false-positive FAST examination.