Nuclide Notes

🧬 READ WITH ME | FDG PET/CT scan

🗓 72-year-old male with history of moderately differentiated hepatocellular carcinoma, referred for staging.

☢️ Findings:

🎯 Hypermetabolic malignant poorly defined hepatic geographical hypodensities with portal vein and its branches tumorous thrombus/infiltration.
🎯 Prominent sized mildly hypermetabolic upper abdominal lymph nodes, likely metastatic.

☢️ Lipomatous hypertrophy of interatrial septum ☢️ FDG PET/CT scan shows a hypermetabolic interatrial well defined ovoid fat attenuation lesion in the interatrial septum, consistent with lipomatous hypertrophy of interatrial septum.
🗓 LHIAS is an uncommon benign fat infiltration of the interatrial septum sparing the fossa ovalis. Usually detected incidentally with 1-8% prevalence rate. It is mostly asymptomatic but surgical excision maybe indicated if they are large, there is underlying arrhythmia or obstructive symptoms. FDG PET scans usually show moderate to intense focal FDG uptake within the lesion.

☢️ Gastric adenocarcinoma intestinal type ☢️ FAPI PET/CT scan shows pyloric concentric mass like wall thickening of intense FAPI uptake with subsequent luminal tapering. Biopsy revealed gastric adenocarcinoma intestinal type.
🗓 Intestinal type gastric tumor is the most common form of gastric adenocarcinoma closely linked with environmental factors and chronic H. Pylori, the other is diffuse type tends to spread in an infiltrative manner causing diffuse wall thickening. Intestinal type tends to grow outwards forming a mass which can be bulky, fungating lesion and usually arises in the lower parts of the stomach.

☢️ Meningiomatosis ☢️ Planar bone scan shows intense tracer uptake involving a confluence of right skull bones and multifocal areas of variable degrees of uptake in multiple left skull bones. SPECT/CT images show extensive marked hyperostotic expansile sclerosis involving the anterior and middle skull base, marked in the right side corresponding to intense delayed tracer uptake. There is associated extra axial paraosseous plaque like dural ossification along the middle cranial fossa. Features suggestive of meningiomatosis.
🗓 Meningiomatosis refers to multiple separate meningiomas which is uncommon with an incidence of 2-10%. It can be sporadic or associated with genetic syndromes such as NF2. While usually an incidental findings clinical impact depends on size, location, mass effect, edema, venous sinus involvement, and proximity to critical neurovascular structures. On bone scan they appear and intense tracer uptake involving the skull and can be mistaken for fibrous dysplasia, Paget disease, metastases…etc. MRI is the modality of choice for mapping disease burden, assessing growth, and guiding surveillance or treatment planning.

☢️ Prone imaging ☢️ A 62 year old male patient referred for a Tc99m-MIBI SPECT MPI under nitrate cover for viability assessment. SPECT MPI revealed a small perfusion abnormality of moderate severity in the anteroseptal wall. There is also mild to moderate perfusion abnormality in the inferior and inferolateral regions. Prone imaging is a cheap and reliable method to exclude diaphragmatic attenuation, in this case the counts in the inferior regions improved significantly after prone imaging (lower row) suggesting diaphragmatic attenuation.
🗓 Prone imaging results in shifting of the heart anteriorly and lowering the diaphragm and subdiaphragmtic organs. The SP of detecting CAD abnormality is significantly increased (61% vs. 84%) without affecting the SN.

☢️ Brucella spondylodiscitis ☢️ 66-year-old male undergoing PET/CT scan for gastric tumor staging with incidental finding of hypermetabolic focal area within the D9-D10 disc space associated with osteolysis in the corresponding vertebral endplates. Upon interviewing the patient he had a history of recurrent treated Brucellosis, recent intermittent fever and complained of vague back pain. CT guided biopsy revealed Brucellosis.
🗓 Brucellosis spondylodiscitis is a significant manifestation of brucellosis. The disease is primarily transmitted to humans through the ingestion of unpasteurized dairy products, direct contact with infected animals, or inhalation of aerosols. Spondylodiscitis is more commonly seen in adults, particularly those involved in agriculture or livestock handling, with a higher prevalence in men. The clinical presentation of brucellosis spondylodiscitis typically includes chronic back pain, fever, night sweats, and general malaise. The lumbar spine is the most frequently affected region, although any segment of the spine can be involved. FDG PET/CT has a SN and NPV for spondylodiscitis but relatively poor SP.
BoneScan

☢️ Complex trilobulated fusiform aortic aneurysm ☢️ involving the descending thoracic and abdominal aorta. On non contrast enhanced images there is a peripheral crescent with hyperattenuation with hounsfield units (HU) higher than patent lumen. This is highly suggestive of impending rupture of the aortic aneurysm. On contrast enhanced images the density should be higher than adjacent psoas muscle attenuation. High attenuating crescent sign is specific represents acute hematoma or bleeding within either mural thrombosis is aneurysmal wall.

🧬 FDG is trapped because FDG-6-P becomes a metabolic dead end.

After FDG enters the cell and is phosphorylated by hexokinase ⚡, it cannot efficiently continue through glycolysis because the 2-fluoro substitution prevents normal isomerization 🔒. It also does not meaningfully enter glycogen synthesis or the pentose phosphate pathway, because it is a poor substrate for those enzymes 🚫.

So the signal we see on PET is not just “glucose use” — it is the result of transport, phosphorylation, impaired downstream metabolism, and limited dephosphorylation 📈.

Understanding this is essential for interpreting FDG uptake patterns, pitfalls, and tumor biology 🧠🩻.

More detailed FDG PET/CT concepts are explained in the PET/CT course on BCV Nuclear Medicine Academy 🎓.

🔗 http://bcv.app/nucmed

☢️ Intercostal vein invasion ☢️ Right poorly differentiated invasive ductal breast cancer with metastases in right axillary lymph nodes and right chest wall. Hypermetabolic lobulated anterior chest wall mass invading and destructing the adjacent part of sternum and rib, protruding posteriorly into the underlying pericardium with adjacent loculated pericardial effusion. The right internal thoracic vein is engorged with intense FDG uptake along its course extending superiorly from the chest wall mass.
🗓 50% of chest wall tumors are malignant and most of them representing metastases from adjacent primary tumors such as breast, lung, mediastinum and pleura. The internal thoracic vein drains the chest wall and respective breast, it arises from the superior epigastric vein, accompanies the internal mammary artery along its course and drains into the braciocephalic vein.

☢️ Langerhan’s cell histocytosis ☢️ FDG PET/CT shows left mandible ramus/body expansive destructive osteolytic lesion of intense FDG uptake with soft tissue component protruding beyond the osseous margins. Additional lytic lesions of intense FDG uptake in the left parietal bone and right ilium. Biopsy revealed LCH
🗓 LCH is a tumor like disease where these cells proliferate in an uncontrollable fashion. This proliferation is accompanied by lesions or mass formation. The skeleton is the most involved organ in LCH, the cells produce prostaglandins which causes medullary bone resorption. Solitary lesions (~70%) are more common than multifocal (~17%), and the most common locations are the skull (50%), ribs/spine/pelvis/femurs (15%), humerus (7%), mandible (7%). Radiologically they have variable appearance depending on location, most commonly as lytic lesions with well defined margins and no sclerotic rims.