PET in Benign Bone Marrow Disorders

Use of bone-SPECT/CT and Na[18F]F-PET/CT in hyperparathyroidism

Hyperparathyroidism disrupts the balance of physiological bone formation and resorption by upregulating osteoclast activity. This leads to hypercalcemia, resulting in osteoporosis and eventually the formation of "brown tumors." Currently used radiological and nuclear medicine imaging for primary hyperparathyroidism face challenges in accurately diagnosing bone-related complications. Molecular bone imaging techniques routinely consist of bone scintigraphy, with possible addition of bone-SPECT/CT. Recently, renewed interest has emerged in the use of Na[18F]F-PET/CT. Both applications are highly sensitive to in vivo osteoblast activity. However, the latter technique offers improved spatial resolution and sensitivity, as well as shorter incubation and faster scanning. This article summarizes current limitations and potential improvements in bone-SPECT/CT and Na[18F]F-PET/CT imaging in selected patients with hyperparathyroidism, compared to other relevant techniques and clinical parameters.

The role of 18FDG-PET imaging in VEXAS syndrome: a multicentric case series and a systematic review of the literature

VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, and somatic) syndrome is characterized by heterogeneous clinical manifestations. Due to the inflammatory nature of this condition, 18-FDG-PET (18-fluorodeoxyglucose-positron emission tomography) might be used to diagnose and monitor the disease. However, no data are available about the most common findings of PET imaging in this disease. For this reason, we summarised all the available reports of patients with VEXAS who underwent at least one PET scan and described 8 additional patients' PET from our centres. Overall, we described 35 patients' PET findings. All patients were male, with a median age of 70 years. The most frequent hypermetabolic sites on PET scans were the bone marrow (77.1%), lymph nodes (35.3%), lungs (28.6%), spleen and large vessels (22.9%), and cartilage (20%). Six patients underwent a PET scan 2.7 ± 1.5 years before VEXAS diagnosis, showing nonspecific uptake in the bone marrow. Four patients had a follow-up PET scan, showing a decrease or a disappearance of the previously identified hypermetabolic areas. In conclusion, although no specific uptake site has been found for VEXAS syndrome, PET imaging could help detect inflammatory foci that are not clinically evident. In addition, high metabolic activity in bone marrow might precede the clinical onset of the disease, shedding light on the pathogenesis of VEXAS.

Extramedullary Hematopoiesis in Treated Diffuse Large B-Cell Lymphoma of Bone

ABSTRACT

A 65-year-old man with a history of diffuse large B-cell bone lymphoma of the right radius underwent an interim FDG PET/CT after 2 cycles of chemotherapy. Besides a complete metabolic response on the primary site, images revealed a hypermetabolic nodule in the posterior mediastinum, not present on the initial images. The metabolic activity of the nodule was similar to that of the reactive bone marrow and disappeared, concomitantly to the normalization of the medullar signal on the posttreatment images. The similarity and synchronous metabolic activity evolution in the nodule and bone marrow indicate extramedullary hematopoiesis.

18F-Fluorothymidine PET for Functional Response Assessment Following Radiation Therapy for Extramedullary Hematopoiesis

ABSTRACT

As a marker of cellular proliferation, 18F-fluorothymidine (FLT) PET can detect the distribution of proliferating hematopoiesis and has an emerging role in the investigation of hematopoietic disorders. These images demonstrate the novel utility of 18F-FLT PET for imaging sites of extramedullary hematopoiesis (EMH) in a patient with Chuvash-type polycythemia and suggest a role for 18F-FLT PET in response assessment following radiotherapy. Further, the discordant response observed in the irradiated marrow and sites of EMH is a unique discovery, possibly suggesting the influence of the microenvironment favoring more rapid recovery of proliferative function within EMH sites.

Lenograstim-Induced Nodal Extramedullary Hematopoiesis: A Challenging Diagnosis in Lymphoma Evaluation With 18F-FDG PET/CT

We report the case of a 23-year-old man with nodal EMH (extramedullary hematopoiesis) occurring during treatment for a stage IIA "gray-zone" lymphoma. Although it is often related to myeloproliferative bone marrow disease, benign etiologies such as lenograstim treatment after chemotherapy can also induce EMH and be responsible for false-positive F-FDG PET/CT examinations. In this respect, GLUT overexpression in hematopoietic lineages and macrophages of the inflammatory environment are responsible for increased F-FDG uptake. Histopathologic confirmation of new hypermetabolic lesions on follow-up PET/CT may be required when the new lesions do not conform with the treatment responses in the preexisting lesions.

Marrow outside marrow: imaging of extramedullary haematopoiesis

Extramedullary haematopoiesis (EMH) refers to the formation of non-neoplastic blood cell lines outside the bone marrow and is a common incidental finding when patients with haematological disorders are imaged. EMH presenting as mass (tumefactive EMH) has long been a radiological conundrum as it resembles neoplasms. Several imaging findings have been described in EMH, and these vary depending on the activity of the underlying haematopoiesis. The older lesions are easier to diagnose as they often demonstrate characteristic findings such as haemosiderin and fat deposition. In comparison, the newer, actively haematopoietic lesions often mimic neoplasms. Molecular imaging, particularly ^99mTc labelled sulphur colloid scintigraphy, may be helpful in such cases. Although imaging is extremely useful in detecting and characterising EMH, imaging alone is often non-diagnostic as no single mass shows all the typical findings. Hence, a judgement based on the clinical background, combination of imaging findings, and slow interval growth may be more appropriate and practical in making the correct diagnosis. In every case, an effort has to be made in providing an imaging-based diagnosis as it may prevent a potentially risky biopsy. When confident differentiation is not possible, biopsy has to be resorted to. This article describes the causes, pathophysiology, and theories underlying the genesis of EMH, followed by the general and location-specific imaging findings. The purpose is to provide a thorough understanding of the condition as well as enable the clinical radiologist in making an imaging-based diagnosis whenever possible and identify the situations where biopsy has to be performed.

Hereditary Spherocytosis Presenting as Diffuse Bone Marrow Activation and Splenomegaly on PSMA-Targeted 18F-DCFPyL PET/CT

We present the case of a 71-year-old man with Gleason 3 + 3 = 6 pT2N0MxR0 adenocarcinoma of the prostate who presented with rising PSA level 16 years after radical prostatectomy. PSMA-targeted F-DCFPyL PET/CT was performed, which demonstrated recurrent disease in the prostatectomy bed as well as splenomegaly and mild-diffuse bone marrow activation, consistent with the patient's history of hereditary spherocytosis. We briefly review the clinical characteristics of hereditary spherocytosis, its appearance on molecular imaging studies, the normal biodistribution of F-DCFPyL, and the PSMA-RADS scoring system for characterizing findings on PSMA-targeted PET imaging.

SPECT/CT in the Postoperative Painful Knee

This review summarizes the role of SPECT/CT in patients with a painful postoperative knee and describes typical diagnostic criteria in these patients. Pain after knee surgery is common and is influenced by the underlying pathology, the type of surgery, and the patient. Knee joint-preserving surgery includes osteotomy, ligament reconstruction, meniscus surgery, and cartilage repair procedures, often used in combination. Knee arthroplasty procedures consist of unicondylar, patellofemoral, and primary or revision total knee prosthesis. In patients with pain after knee joint-preserving surgery, MRI remains the reference standard. After ligament reconstruction, CT can evaluate postoperative tunnel positioning, and bone SPECT/CT can contribute by assessing overloading or biodegradation problems. After meniscal or cartilage surgery, SPECT/CT can be particularly helpful to identify compartment overloading or nonhealing chondral or osteochondral lesions as cause of pain. SPECT/CT arthrography can assess cartilage damage at an early stage due to altered biomechanical forces. After corrective osteotomy of the knee, SPECT/CT can reveal complications such as overloading, nonunion, or patellofemoral problems. After arthroplasty, conventional radiographs lack both sensitivity to detect aseptic loosening and specificity in differentiating aseptic from infectious loosening. Secondly, hardware-induced artifacts still hamper CT and MRI, despite improving and increasingly available metal artifact reduction techniques. Bone scintigraphy is a proven useful adjunct to conventional radiography and MRI to reveal the pain generator and is less hampered by artifacts from metallic implants compared with CT and MRI. Nevertheless, the optimal imaging strategy in evaluating complications after knee arthroplasty is still a matter of debate. Although the evidence of the use of BS SPECT/CT is still limited, it is growing steadily. In particular, recent data on specific uptake patterns in tibial and femoral zones after total knee arthroplasty and the impact of integrating biomechanics into the assessment of SPECT/CT appear promising, but more research is needed.