Abstract
Objective
2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography ([18F]-FDG PET/CT) can be developed in association with contrast-enhanced CT (ceCT), specifically in oncologic patients. This study aimed to evaluate emergency cases incidentally detected in our clinical practice with [18F]-FDG PET/ceCT.
Method
We retrospectively evaluated 3661 [18F]-FDG PET/ceCT, developed between 2017 and 2023, collecting emergency cases needing prompt treatment.
Results
In 34/3661 patients (0.9%) an emergency case was recorded, in particular through contrast-enhanced CT, linked to a vascular (65%) or extravascular (35%) disease. The more frequent findings were pulmonary thromboembolism (0.5%). [18F]-FDG PET/CT was positive in 13/34 cases.
Conclusions
A significant minority of patients undergoing PET/ceCT present vascular or extravascular emergency diseases. The [18F]-FDG uptake improves confidence in diagnosing inflammatory findings. Properly trained diagnostic physicians approaching PET/ceCT can change the prognosis of a small but significant number of cancer patients through a life-saving approach. Future studies are needed to ensure the possibility of emergency findings with non-[18F]-FDG tracers.
Introduction
2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography ([18F]-FDG PET/CT) is the standard whole-body imaging method used in cancer imaging, allowing the definition and monitoring of glucose metabolism with a focus on personalized care and prognostication in numerous malignant diseases; as a glucose analog, [18F]-FDG is a marker of cell vitality, potentially leading to misdiagnoses due to its uptake in inflammatory and benign lesions. Moreover, more malignant tumors do not show meaningful uptake [1].
Nuclear physicians improved their expertise in the low-dose CT component of the exam to overcome these limitations, with a beneficial impact on the diagnostic accuracy of PET/CT.
However, several groups routinely associate PET/CT scans with full-dose contrast-enhanced CT (ceCT); PET/ceCT allows precise tumor depiction, enabling differentiation from surrounding structures, assessing tumor resectability, and improving the characterization of non [18F]-FDG-avid lesions.
Beyond ceCT, from this hybrid point of view, radiologists exploit metabolic PET data, while nuclear physicians take advantage of CT information on tumor extension, lymph nodes, and distant metastases, mutually reinforcing their confidence in the diagnosis [2].
Worldwide, a variable number of PET/ceCT scans are performed: [18F]-FDG PET/ceCT plays a clear role in patients with ovarian cancer [3], liver metastases [4], urothelial cancer [5], and large vessel vasculitis [6]. Nevertheless, its role in hematology is still controversial [7], while the association of ceCT with PET with radiopharmaceuticals other than [18F]-FDG has been discussed due to the relatively higher specificity of other PET tracers, such as prostate cancer agents [8].
In our department, we perform [18F]-FDG PET/ceCT in selected patients with suspected brain metastases, peritoneal carcinomatosis, and liver metastases to assess the T-stage of abdominal neoplasms and their secondary localizations, as well as in the staging and assessment of the end of treatment in lymphomas; less frequent indications for performing [18F]-FDG PET/ceCT are breast cancer and lung cancer, colon carcinoma, pancreatic cancer, chronic lymphocytic leukemia, laryngeal cancer, and various sarcomas.
In these clinical settings, using [18F]-FDG PET/ceCT, we documented and collected some emergency cases that required prompt treatment due to the high risk to the patient's life. All patients were obviously asymptomatic or paucisymptomatic at the time of examination.
All PET/CT examinations were conducted for oncological suspicion or a known oncological diagnosis. In no case was a clinical presentation found at the time of admission that would disregard or initiate a diagnostic process for suspected diagnostic emergencies.
To the best of our knowledge, Flavell et al. systemically reported an incidence of 0.32% pulmonary embolism in a large population of cancer patients examined by [18F]-FDG PET/ceCT [9].
Our study aimed to discuss the emergency cases that we encountered in our clinical practice with PET/ceCT, which are typically performed for cancer staging, restaging, and follow-up. We chose not to compare the diagnostic accuracy of PET/CeCT to that of other techniques because CT is the most appropriate method for detecting clinical emergencies [10]. In particular, we focused on radiological semiotics and the complementarity between PET/CT and ceCT, with emphasis on the peculiar features of these emergency cases.
Patients and methods
We retrospectively analyzed all [18F]-FDG PET/ceCT scans performed in our Department of Hybrid and Molecular Imaging from January 2017 to December 2023.
Only [18F]-FDG PET/ceCT scans of outpatients were included in the study since we occasionally administer contrast agents during scans performed with radiopharmaceuticals other than [18F]-FDG. Patients with both pneumonia and skeletal fractures were excluded from the series because these findings are easily recognizable during routine practice with PET/CT. On the other hand, we have chosen to describe subjects with pneumothorax; ceCT is not usually required to diagnose this condition but, due to the intrinsic clinical implications, pneumothorax can be considered potentially associated with acute symptoms (shortness of breath, chest pain) often requiring a prompt surgical approach. Moreover, other conditions such as hemothorax, pulmonary embolism, and heart attack, may potentially present symptoms overlapping, thus requiring further steps, more likely ceCT, for the differential diagnosis.
Patient data were cross-referenced with the electronic medical records of the hospital, particularly with access to the Emergency Department of our hospital.
Overall, emergency ceCT findings were reported in the form of a Preliminary Report for Rapid Communication with the Emergency Department; in some particularly serious cases, telephone communication was also an additional option. However, the final reports were available in a short time and included a conjoint translational conclusion between a radiologist and a nuclear physician. After the initial treatment in the Emergency Department, the patients were transferred to clinical oncology, general internal medicine, general or vascular surgery, urology, and hematology, depending on the underlying disease.
Data collection
Whole-body PET/CT scans were evaluated by six nuclear physicians (FC, RT, MT, SC, AL, and AB). All ceCT scans associated with PET were reviewed by a dedicated radiologist (ML) with more than ten years of experience in hybrid nuclear medicine.
The included PET/ceCT scans were analyzed separately ad hoc by a nuclear physician and a radiologist on a dedicated workstation for PET/CT and ceCT, respectively; subsequently, the final diagnosis was reached via a consensus.
All readers had access to the patient's medical history and electronic medical records.
The presence of pulmonary embolism, complicated visceral/parenchymal inflammation, or other emergency cases was determined by the commonly accepted methodology [11].
Technical notes
All patients fasted for at least 6 h before intravenous [18F]-FDG administration, and their serum glucose levels ranged from 76 mg dL−1 to 132 mg dL−1. Patients were injected with 220–390 MBq of [18F]-FDG and hydrated (500 ml of 0.9% i.v. saline sodium chloride (NaCl)) to reduce the pooling of the radiotracer in the kidneys. Water (500–600 cc) was administered per os during the uptake time to complete hydration and to delineate the intestinal loops on CT; when clinically requested, oral positive or negative contrast agents were used.
PET/CT scans were acquired using a Discovery scanner (Discovery PET/CT 710, General Electric Medical Systems, GE, Milwaukee, WI, USA). A low-amperage CT (low-dose CT) scan was acquired for attenuation correction of the PET images [80 mA, 140 kV, field of view (FOV) approximately 420–500 mm, CT slice thickness 3.75]. Subsequently, whole-body PET examination in the cauda-cranial direction (5–7 bed positions, 3 min per bed, from the upper thighs to the vertex) was performed 60 min after tracer administration. Images were reconstructed using a standard iterative algorithm [ordered subset expectation maximization (OSEM)].
Following the PET scan, a whole-body ceCT scan [100–140 kV, automatic milliamperage (limit 350–400 mA), thickness 2.500 mm, interslice interval 1.25 mm, table speed 39.37 mm/rot., Pitch 0.984:1, gantry rotation time 0.5 s, large body FOV, matrix 512 × 512] was planned with the same scout view and carried out with intravenous administration of nonionic iodinated contrast material (iodine concentration solution: 320 or 400 mg mL−1, volume: 80–100 mL at a flow of 2–4 mL s−1) and a subsequent saline bolus (volume: 20–30 mL).
The protocols of the ceCT study included head or neck and single-phase or multiphase acquisitions based on the clinical indication and the examination request.
Results
Overall, 3830 PET/ceCT scans were performed using [18F]-FDG, [18F]FDOPA, [18F]choline, [68Ga]-PSMA, and [68Ga]-DOTATOC.
A total of 169 PET/ceCT scans with tracers other than [18F]-FDG were excluded. We included 3661 PET/ceCT scans with [18F]-FDG; among these scans, 35 [18F]-FDG PET/CeCT scans were retrospectively selected, revealing an emergency case. One of these patients had missing data at the follow-up and was hospitalized at another center (Fig. 1).
Emergency cases selection process.
[18F]-FDG PET/ceCT, [18F]Fluorodeoxyglucose Positron Emission Tomography/contrast-enhanced Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
The documented 34/3661 emergency cases were associated with the following diseases: Hodgkin's and non-Hodgkin lymphomas, breast cancer, lung cancer, colorectal cancer, chronic lymphocytic leukemia, laryngeal cancer, pleomorphic sarcoma, paraneoplastic syndrome and one case of lymphoproliferative disorder of unknown origin.
Among these patients, 14/34 were receiving chemotherapy and/or immunotherapy (41%), 6/34 had prior surgical resection of a primitive neoplasm (17%), 8/34 had undergone radiation therapy (23%), and 19/34 had not received treatment (55%). All examined patients with somatic cancer presented metastatic spread.
After the preliminary analysis, the series was divided into two groups, i) vascular and ii) extravascular emergency cases, according to the documented findings. These data are summarized in Table 1.
The table summarizes the case series with the final diagnosis of incidental disease at PET/ceCT. In addition, the contribution of the [18 F]-FDG PET/CT low dose is quantified
| No. of cases | Clinical indications for [18F]-FDG PET/ceCT | Incidental emergencies (final diagnosis) | Incidental emergencies PET-detected (No. of cases with [18F]-FDG uptake) | Incidental emergencies PET-aided (No. of cases in which [18F]-FDG uptake assists in making the final diagnosis) | |
| Vascular Emergency cases | 20 | n = 13 Staging or EOT evaluation of NHL | Acute pulmonary embolism with/without infarct (Fig. 2) | 4 (pulmonary uptake) | – |
| n = 3 FU of lung cancer | |||||
| n = 1 Staging pleomorphic sarcoma | |||||
| n = 2 FU of breast cancer | |||||
| n = 1 Staging of laryngeal cancer | |||||
| 1 | FU of CLL | Splenic pseudoaneurysm complicating pancreatitis (Fig. 3) | 1 (pancreatic uptake) | 1 | |
| 1 | FU of SCLC | Type 3 Endoleak | 1 (extra prosthetic uptake) | – | |
| Extravascular Emergency cases | 2 | n = 1 EOT evaluation of NHL | Acute complicated appendicitis (Fig. 6) | 2 (uptake in RIF) | 2 |
| n = 1 Staging of CRC | |||||
| 4 | n = 1 Paraneoplastic syndrome | Pneumothorax (Fig. 4) | – | – | |
| n = 3 FU of NSCLC | |||||
| 2 | n = 1 Suspicious of lymphoproliferative disorder | Complicated diverticular disease (Fig. 5) | 2 (colon and pericolic uptake) | 2 | |
| n = 1 FU of inoperable lung cancer | |||||
| 2 | n = 1 FU of CRC | Acute complicated cholecystitis | 2 (gallbladder and pericholecystic liver uptake) | 2 | |
| n = 1 FU of breast cancer | |||||
| 1 | Staging of NHL | Splenic rupture (Fig. 7) | 1 (splenic uptake) | – | |
| 1 | FU of HL | Lithiasic pyonephrosis | – | – | |
| Tot. | 34 | – | – | 13 | 7 |
ceCT, contrast-enhanced Computed Tomography – CLL, Chronic lymphocytic leukemia – CRC, Colorectal Cancer – EOT, end-of-treatment – FU, follow-up – NSCLC, Non-small cell lung cancer – NHL, non-Hodgkin's Lymphoma – HL, Hodgkin Lymphoma – RIF, Right iliac fossa – SLCL, Small cell lung cancer – [18F]-FDG PET/CT, [18F] Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography.
According to our data, the incidence rate of emergent disease on [18F]-FDG PET/ceCT scans was 0.9%, and more than half (0.5%) of our population had pulmonary embolism. The mean age was 62 years (range 51–83).
Vascular emergencies were detected in the majority of these patients (22/34; 65%). Among these patients, 20 had acute pulmonary embolism, one had splenic pseudoaneurysm complicating pancreatitis, and one had type 3 endoleak.
Extravascular emergencies were documented in 12/34 patients (35%), represented by pneumothorax (n = 4), acute complicated appendicitis (n = 2), complicated diverticular disease (n = 2), acute complicated cholecystitis (n = 2), splenic rupture (n = 1), and lithiasic pyonephrosis (n = 1).
PET/CT alone detected high uptake of [18F]-FDG associated with both acute intravascular and extravascular alterations in 13/34 patients diagnosed by ceCT (38%); in particular, [18F]-FDG uptake was detected in 6/22 patients (27%) with vascular emergencies and 7/12 patients (58%) with extravascular diseases.
Discussion
Emergency cases were documented in 0.9% of the examined patients—a significant minority—due to the underlying disease and/or concurrent therapies. Cancer patients are vulnerable to infections, and the risk is increased by tumor-associated immunosuppression and the effects of neutropenia induced by cytotoxic chemotherapy [12], with increasing morbidity and mortality [13]. Diagnostic physicians need to be aware that the incidence of vascular disease in cancer patients will increase due to the increasing use of modern chemotherapies and the prolonged survival of cancer patients [14].
The above considerations help to explain the relatively high rate of vascular emergencies. According to the literature, 15% of cancer patients may develop clinically significant venous thromboembolism, the second leading cause of death among cancer patients undergoing chemotherapy [12]. We found a remarkable number of cases of acute pulmonary embolisms connected to hypercoagulability associated with malignant diseases or to the side effects of chemotherapy and immunotherapy [15]. The identification of thromboembolism by ceCT has a significant impact on daily life and patient survival; pulmonary embolism may show [18F]-FDG uptake; it has been hypothesized that the presence of a thrombus within a pulmonary artery determines acute distension, inflammation, and focal necrosis of the vessel wall with the aggregation of leukocytes along the endothelial surface with a consequent focal increase in 18F-FDG uptake in inflammatory cells at the embolic site [16]; [18F]-FDG uptake in pulmonary infarction has been mostly described as an incidental finding in whole-body cancer staging [18F]-FDG PET/CT [17]. The uptake pattern observed in pulmonary infarction on [18F]-FDG PET/CT is called the “rim sign” [18].
Conversely, acute pulmonary embolism in ceCT is identified as an intraluminal filling defect with a sharp interface with intravascular contrast in the form of a complete opacification defect, a central opacification defect surrounded by intravascular contrast, or a peripheral intraluminal filling defect showing an acute angle to the arterial wall [19]. In our series, the pulmonary embolism finding was incidental during the venous phase scan, so a dedicated acquisition has never been performed. Despite this, the venous phase acquisition does not limit the visualization of the endovascular filling defect; it simply requires greater experience and visual intuition.
Pulmonary infarction on CT scan is a peripheral, triangular consolidation with central lucency located in the expected vascular distribution of the associated embolism [20].
However, in all our patients, ceCT showed a thromboembolic defect within the artery without consensual [18F]-FDG uptake; in a few patients with concomitant pulmonary infarction, [18F]-FDG rim uptake at the site of peripheral wedge-shaped consolidation with central foci of hypoattenuation and low enhancement was observed (Fig. 2).
Incidental embolism and peripheral pulmonary infarct. Coronal reconstruction and axial ceCT images (a, c) show a long embolic filling defect (white arrows) in the segmental lateral-basal artery of the right lower lobe, with pulmonary infarction (white asterisk). Axial PET/CT view (d) shows sub-pleural [18F]-FDG rim uptake (double white asterisk) in the basal opacity. Axial CT image of lung parenchyma (b) shows wedge-shaped consolidation with central foci of hypoattenuation (black asterisk) corresponding to the infarction caused by pulmonary embolism.
ceCT, contrast-enhanced Computed Tomography – [18F]-FDG, [18F]Fluorodeoxyglucose – PET/CT, Positron Emission Tomography/Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
Furthermore, 0.5% of our population presented CT and/or PET findings indicative of pulmonary embolism (20/3661).
Interestingly, these data are similar to the results of Flavell et al. [9], who reported pulmonary embolism in 0.32% of 18,272 cancer patients examined by 18F-FDG PET/ceCT.
Among the other vascular emergency diseases, a case of endoleak was reported, presenting as an accumulation of [18F]-FDG outside the stent graft within the abdominal aortic aneurysm sac [21].
[18F]-FDG uptake correlates with the development of an endoleak and/or with the progression of dilation of the aneurysm sac. If the preprocedural PET is positive, the risk of postprocedural growth of the aneurysm increases [22]. In our case of a type 3 endoleak with a defect between the components of the modular grafts, the site of accumulation of the extraprosthetic contrast medium coincided with the extraprosthetic aneurysmatic [18F]-FDG uptake.
As the last vascular finding, pseudoaneurysms of the splenic artery were found in pseudocysts on CT, appearing as focal areas of enhancement within the low-density fluid inside the cyst, continuing with the artery [23]. Concurrent [18F]-FDG-avid pancreatitis was documented. Pancreatitis can present a variety of CT features, ranging from a pancreas without abnormalities to an enlarged gland with heterogeneous attenuation, a poorly defined border of the gland, and a stranding appearance of periglandular fat [24]. On [18F]-FDG PET/CT, the pancreas may be diffusely enlarged with loss of lobulation, demonstrating diffuse or heterogeneous 18F-FDG uptake [25], as in the documented case (Fig. 3).
Splenic pseudoaneurysm complicating pancreatitis. MIP (a) and axial PET (b) images detect diffuse [18F]-FDG uptake in the pancreas (arrows) with internal non [18F]-FDG-avid area (asterisk), corresponding to a giant splenic artery pseudoaneurysm (asterisk) caused by underlying pancreatitis in related ceCT (c) and axial PET/CT views (d).
ceCT, contrast-enhanced Computed Tomography – FDG, Fluorodeoxyglucose – MIP, Maximum Intensity Projection – PET/CT, Positron Emission Tomography/Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
Concerning extravascular emergencies, we mainly observed cases of pneumothorax, followed by acute diverticulitis, complicated appendicitis, and cholecystitis.
Pneumothorax can occur spontaneously when the underlying lung is abnormal, such as in cases of necrotic neoplasms with cavitation, radionecrosis, or pulmonary infarction; other causes are iatrogenic following biopsy or lung surgery [26]. Pneumothorax was classified as a “critical finding” of major importance in a previous similar study, representing the most frequent unexpected emergency disease detected by [18F]-FDG PET/CT [27]. In our series, ceCT was useful for diagnosis, allowing the identification of the lucency within the pleural space, usually at the anterior lung base or along the mediastinal pleura, associated with a definite separation of the visceral pleura from the parietal pleura. On PET/CT, pneumothorax may appear as a curvilinear area of photopenia between the inner thoracic wall and the edge of the lung [28]. On CT images, it was possible to easily detect pleural air flow corresponding to [18F]-FDG uptake deficiency with widespread consensual and mild uptake by the collapsed lung parenchyma with a more or less evident mediastinal shift (Fig. 4).
Pneumothorax after lung surgery. Axial (a) and sagittal PET views (b) display a non [18F]-FDG-avid collection of pleural air (asterisk) and tracer uptake in dislocated lung parenchyma; the drawn line defines the curved contour of the interface between the inner chest wall and the edge of the lung. Axial CT image, with pulmonary window (c), and sagittal PET/CT views (d) displays the airspace (asterisk) along the front appearance of the right hemithorax, corresponding to the postsurgical pneumothorax.
CT, Computed Tomography – FDG, Fluorodeoxyglucose – PET, Positron Emission Tomography – PET/CT, Positron Emission Tomography/Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
Different considerations concern acute diverticulitis and complicated appendicitis. On CT, diverticulitis appears as long colonic wall thickening characterized by hyperemic changes and thickening of the peri-visceral fat. A diverticular abscess appears as a fluid, fluid-air, or hypodense collection of necrotic tissue with surrounding inflammatory changes. Contained focal perforations may appear as small extraluminal air pockets or as extravasation of oral contrast material. Pneumoperitoneum is not a common finding in patients with diverticulitis and microperforations [29]. It is known that in 1% of PET/CT studies, focal uptake in the colon may be associated with a high risk of malignant or precancerous lesions (65%); focal [18F]-FDG colic uptake is potentially related to a neoplasm, while segmental uptake is generally associated with inflammatory processes [30].
In one of our patients, the ceCT scan revealed diverticulitis with parietal perforation, extraluminal collections, pericolic inflammatory changes, and bubble gas in the right subphrenic region; PET/CT confirmed high diverticular [18F]-FDG uptake surrounding these findings and in the retrohepatic region (Fig. 5).
Complicated diverticular disease with pelvic peri-diverticular collection and pneumoperitoneum. MIP PET and axial PET/CT views show focal diverticular uptake (a, black arrow, d, solid white arrow) and peripheral abscess uptake, with concurrent tracer-avid lung neoplastic mass and mediastinal lymphadenopathy (a, boxes). CeCT shows complicated acute sigmoid diverticulitis (b, empty white arrow), with extraluminal inflammatory changes surrounding-two fluid-air abscesses adjacent to the sigmoid diverticula (c, asterisk) and the intrapelvic free air collection (c, double asterisk); extraluminal free air bubbles collected in the right sub-phrenic area are also identified (b, rectangular box).
ceCT, contrast-enhanced Computed Tomography – MIP, Maximum Intensity Projection – PET/CT, Positron Emission Tomography/Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
CT signs of acute appendicitis include thickening of the appendicular wall, significant improvement in tissue contrast enhancement, and layering of the appendicular mural, appendicolitis, and intramural gas. Complications of acute appendicitis include fat stranding, thickening of the lateroconal fascia and mesoappendix, extraluminal fluid, phlegm, abscess, and enlargement of lymph nodes [31]. [18F]-FDG uptake in this inflammatory condition has been incidentally documented in the appendix or the cecum [32]. In two patients, PET/CT revealed ring uptake at the mass-forming abscess in the right iliac fossa and focal uptake in the peri-appendiceal area with fat stranding and enhancing wall thickening at ceCT due to appendicitis (Fig. 6).
Acute complicated appendicitis with a peri-appendiceal mass-forming abscess. MIP PET (a) and axial PET (b) views show [18F]-FDG uptake in the RIF, corresponding to a mass-forming abscess, displayed in correlative axial ceCT image (c, empty white arrow). Axial PET/CT views confirm tracer uptake along the margins of the abscess (d, solid white arrow).
ceCT, contrast-enhanced Computed Tomography – FDG, Fluorodeoxyglucose – MIP, Maximum Intensity Projection – PET/CT, Positron Emission Tomography/Computed Tomography – RIF, right iliac fossa
Citation: Imaging 2025; 10.1556/1647.2024.00272
In acute cholecystitis, ring-like [18F]-FDG uptake can be observed in the gallbladder [33], while the typical features of acute cholecystitis on CT are distention, wall thickening with increased mucosal impregnation, cholecystic calculi, and a pericholecystic fluid layer; pericholecystic abscess may show intramural fluid collections and possible mass-like extension to the liver parenchyma and omental thickening [34]. In our case series study, we observed these CT features in association with intense ring [18F]-FDG uptake; in one patient, extensive [18F]-FDG-avid liver infiltration was also observed.
In the registered case of pyonephrosis, calico-pelvic dilation with parietal enhancement on ceCT was documented, without meaningful information provided by PET/CT. Due to the renal excretion of [18F]-FDG, the renal pelvis usually displays high urinary radioactivity, thus leading to difficulty in observing pyelonephritis via PET/CT [1]. CT can be used to diagnose pyonephrosis by identifying obstructive dilatation (lithiasis) and gas‒fluid or fluid‒fluid levels in the intrarenal collecting system. Additionally, thickening of the renal pelvis wall (>2 mm) and inflammatory changes in the parenchyma or perirenal area with fluid suffusion or collections are often observed [35].
A case of splenic rupture was documented; this rare condition mainly occurs in patients with marked splenomegaly because of underlying hematologic malignancies. To our knowledge, no cases of splenic rupture have been documented on PET/CT. Lymphomatous splenic involvement is documented on CT with a splenic index above 725 cm3 or low attenuation nodules; the commonly used criterion for defining splenomegaly in practice is a height of 13 cm from the top to the bottom of the spleen, as measured by ultrasonography or CT; ceCT allows the identification of a grossly abnormal spleen with perisplenic hemorrhage and a clot in the organ [36] that can be associated with hemoperitoneum, often with a mixed appearance or fluid‒fluid level. Intrasplenic active hemorrhage is characterized by jet-like extravasation of injected contrast medium at ceCT, with attenuation of blood vessels at all stages of acquisition. On [18F]-FDG PET/CT, the degree of splenic uptake is assessed visually and scored according to its relation to hepatic uptake. In our patient, PET/CT revealed splenomegaly with diffuse [18F]-FDG uptake and increased tracer accumulation along the subcapsular fissure lines (Fig. 7).
Splenic rupture. MIP PET (a, box) and axial PET view (b) show tracer-avid splenomegaly with stripes of more intense uptake (solid white arrow), confirmed by coronal ceCT view (c) also displaying hypodense subcapsular lines due to laceration (empty white arrow). Coronal PET/CT view (d) shows the splenomegaly with evident inversion of the hepato-splenic axis of glucose metabolism and intra-splenic stripes of more intense uptake, corresponding to the fissure lines (d, empty white arrow).
ceCT, contrast-enhanced Computed Tomography – MIP, Maximum Intensity Projection – PET/CT, Positron Emission Tomography/Computed Tomography
Citation: Imaging 2025; 10.1556/1647.2024.00272
All registered PET/CT findings, when observed, helped radiologists reach the diagnosis with major confidence. However, it is necessary to state that [18]F-FDG uptake was recorded in a minority of the recorded cases. This feature could be due to the more accurate visualization of vascular findings as well as inflammatory processes by ceCT [37]. Therefore, the real impact of emergency cases on conventional PET imaging with low-dose CT can be underestimated; since low-dose CT is widely used in clinical practice, nuclear physicians should consider the possibility of ensuring suspicious findings on PET/CT with further diagnostic steps. These findings were recently defined as actionable findings by Mattana et al. [38]. Thus, the suspicion of pulmonary embolism, infections, and/or pneumothorax on conventional PET/CT should be further investigated with segmental ceCT.
On the other hand, considering the large number of documented non [18F]-FDG-avid findings, the identification of these emergency cases via conventional PET/CT imaging remains unknown.
As documented, information provided by PET/CT on thromboembolism is limited; uptake is not constantly associated with pulmonary infarction and, without coregistered ceCT, can easily be mistaken for inflammatory thickening. Nevertheless, in cholecystitis, pancreatitis, diverticulitis, and other inflammatory processes, [18F]-FDG PET/CT may improve confidence.
Despite the diagnostic benefits of both conjoint diagnostic tools in a single imaging session (81), in the staging and assessment of the response to therapy, it is not conceivable to combine them routinely; in the era of personalized and multidisciplinary medicine, the use of the low-as-reasonably achievable level dosimetric principle is a clinical-anamnestic criterion for identifying indications for PET/ceCT studies [19] and for minimizing radiation exposure.
A limitation of our study is the exclusion of severe pneumonia and fractures to standardize the case series, as these findings are easily recognizable via conventional PET/CT. This can lead to an underestimation of the real impact of the overall number of emergency cases.
Moreover, we considered only [18F]-FDG due to the low number of ceCTs performed with PET/CT with other tracers, which was not useful for a significant statistical analysis. As new radiopharmaceuticals are becoming more prevalent in nuclear medical imaging, we are uncertain about their influence on the diagnosis of acute emergencies. For instance, radiolabeled PSMA for PET prostate cancer imaging demonstrates high endothelial tropism; this feature needs to be investigated to assess its potential impact on the incidental diagnosis of pulmonary embolism and vascular damage [39].
In conclusion, a significant minority of the examined patients (0.9%) presented with emergency findings potentially affecting patient prognosis quoad vitam.
Radiologists should be able to identify and differentiate these acute conditions from oncologic findings while interpreting the CT of the PET/ceCT scan. A Preliminary Report is a necessary tool for timely communication to the Emergency Department [40], especially when performed by radiologists with skills in cancer imaging and vascular diseases, by facilitating rapid patient care and limiting the need to wait for a longer reporting process for PET/ceCT.
Pulmonary embolism is the most frequent emergency case in which ceCT is crucial. The combination of ceCT and PET/CT with a hybrid approach provides complementary information, mutually reinforcing confidence in the diagnosis.
Authors' contribution
Mario Leporace: Conceptualization, Methodology, Investigation, Resources, Writing-Reviewing And Editing, Data Curation Ferdinando Calabria: Conceptualization, Methodology, Investigation, Resources, Writing-Reviewing And Editing, Data Curation Rosanna Tavolaro: Resources, Data Curation Maria Toteda: Resources, Data Curation Stefania Cardei: Resources, Data Curation Antonio Lanzillotta: Resources, Data Curation Giuliana Guadagnino: Resources, Data Curation Antonio Bagnato: Resources, Data Curation.
Funding sources
None.
Conflict of interests
Nothing to declare.
Ethical statement
This study was performed in accordance with the ethical standards of the local research committee and with the 1964 Helsinki declaration.
Supplementary material
Supplementary data to this article can be found online at https://doi.org/10.1556/1647.2024.00272.
Acknowledgments
Technical and nursing staff of our Department of Nuclear Medicine and Theragnostics.
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