SNMMI 2021: CT and MRI Appearances of Benign and Malignant Lesions in Prostate Cancer

(UroToday.com) At the 2021 Society of Nuclear Medicine & Molecular Imaging (SNMMI) Meeting’s Correlative Cross-Sectional and Molecular Imaging session, Dr. Preeti Sukerkar discussed CT and MRI appearances of benign and malignant lesions in prostate cancer. Dr. Sukerkar notes that there are several important points to consider when assessing bone lesions, including the patient’s age, history, symptoms, and the lesion size, location and number.

When addressing bone lesions for aggressive versus non-aggressive features, this includes characterizing the margin/zone of transition, periosteal reaction, cortical involvement, soft tissue component, opacity, and degree of matrix/mineralization. As follows are several bone lesions based on appearance:

 

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Characteristics of periosteal reaction include benign, lamellated, speculated/hair on end (perpendicular), sunburst/radial (perpendicular), and Codman Triangle (associated with increasing aggressiveness):

 

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When assessing sclerotic lesions, Dr. Sukerkar notes that the mnemonic “I VINDICATE” is helpful for characterizing these lesions:

  • I – iatrogenic
  • V – vascular   hemangioma, infarct
  • I – infection   chronic osteomyelitis
  • N – neoplasm   primary (osteoma, osteosarcoma) versus metastases (prostate, breast, etc)
  • D – drugs   vitamin D, fluoride
  • I – inflammatory/idiopathic   melorrheostosis, regressed/headed lytic lesions
  • C – congenital   bone islands/osteopoikilosis, osteoporosis, pyknodysostosis
  • A- autoimmune
  • T – trauma   fracture
  • E – endocrine/metabolic   hyperparathyroidism, Paget disease

 

 Prostate cancer bone metastases are often present in the axial skeleton, made up of the pelvis, spine, ribs, skull, clavicles, scapula, and proximal humerus and femur. The typical prostate cancer metastasis pathway is from the Batson’s venous plexus to the pelvis/spine (early on), and then spread to other areas of the body via the red marrow.

 

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Normal marrow on a spine MRI has both T1 and T2 specific characteristics. On T1 phase, hematopoietic marrow shows heterogeneous low T1 signal, but usually is greater > discs/muscle with little to no enhancement. On T2 phase, there is low signal secondary to fat being saturated out, with hematopoietic marrow showing a heterogeneous, slightly high-intensity signal. As follows are the spine MRI characteristics of diffuse prostate cancer metastasis:

 

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 There are several PSMA-avid non-prostate bone lesions, including hemangiomas, fibrous dysplasia, and Paget Disease. Hemangiomas are characterized as osseous venous vascular malformations, with lesions being multiple in 20-30% of cases, and 10-15% of vertebral hemangiomas extending into posterior elements. On MRI, hemangiomas have T1 high signal (secondary to being lipid rich), and low signal trabeculae, whereas T2 high signal has high signal (high water content) and low signal trabeculae. When hemangiomas are suggested on imaging, the differential diagnosis typically includes metastases (decreased signal intensity on T1 and increased signal intensity on T2) and Paget Disease (coarse trabeculae and can be more expansive). Fibrous dysplasia can occur in the ribs, proximal femur, and craniofacial, as depicted in the following figure:

 

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 On plain X-ray, fibrous dysplasia is characterized as endosteal scalloping, intact cortical thinning, and ground glass appearance (though it can also be lucent or sclerotic). On CT scan imaging, fibrous dysplasia of the ribs has expansile bubbly cystic lesions and fusiform enlargement, whereas the sphenoid wing has a ground glass appearance. Finally, on MRI, fibrous dysplasia can be variable, with a heterogeneous signal and enhancement; these lesions can appear aggressive on MRI. When fibrous dysplasia is suggested on imaging, the differential diagnosis is Paget Disease, enchondroma, and hemangioma.

Paget disease is characterized by an early stage of osteoclastic activity and lytic bone lesions. During an intermediate stage, there is osteoblastic and osteoclastic activity with mixed bone lesions, as well as cortical thickening, osseous expansion, loss of corticomedullary differentiation, and coarse trabecular markings. During the late stage, there is decreased osteoblastic activity and osteosclerosis. Intermediate and late stage disease is characterized by a cotton wool appearance, which is described as thickened, disorganized trabeculae, and poorly defined and fluffy sclerosis in a previously lucent area of bone, typically in the skull. On MRI, a Pagetic bone signal is similar to a fat signal (longstanding disease; most common), speckled low T1 and high T2 signal alteration (granulation tissue, hypervascularity, and edema seen in early mixed active disease; second most common), and low T1 and T2 (compact bone/fibrous tissue, late stage, least common). When Paget Disease is the mostly likely diagnosis on imaging, the differential diagnosis in the calvarium includes hyperostosis frontalis interna (thickening of the internal table of the frontal bone) or fibrous dysplasia; in the spine includes hemangioma; and anywhere in the body includes primary malignancy or metastasis (often more aggressive in appearance). As follows is the characteristic images of Paget Disease on MRI:

 

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 Dr. Sukerkar notes that there are several non-prostate malignant bone lesions with reported PSMA uptake in vivo, including multiple myeloma, sarcomatous transformation of fibrous dysplasia, chondrosarcoma, papillary thyroid carcinoma, renal cell carcinoma, hepatocellular carcinoma, and non-small cell lung cancer.

 

With regards to solitary rib lesions, Dr. Sukerkar emphasized that most are benign with relatively low uptake, with a differential diagnosis of a solitary rib lesions including:

  • Metastases
  • Fibrous dysplasia (most common benign rib lesion)
  • Fracture/post-traumatic
  • Paget Disease
  • Osteomyelitis
  • Primary malignancy

 

Dr. Sukerkar concluded her presentation with the following take home messages:

  • It is important to obtain the relevant patient history and symptoms
  • Conventional imaging of PSMA-avid bone lesions should take into consideration location and characteristic features on different imaging modalities. If imaging is atypical for prostate cancer metastases, clinicians should consider common false positives such as hemangioma, fibrous dysplasia, and Paget Disease
  • There is special consideration for rib lesions, including a differential diagnosis of metastases, fibrous dysplasia, and trauma
  • Clinicians should assess for change over time if uncertain, in order to compare to prior imaging, if available, and to follow-up to assess stability
  • Biopsies should be considered if indeterminate or unexpected changes over time occur and if intervention would affect clinical management

 

Presented by: Preeti Sukerkar, MD, Ph.D., assistant clinical professor in the Musculoskeletal Imaging Section, University of California – San Francisco, San Francisco, CA

Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the Society of Nuclear Medicine & Molecular Imaging – 2021 Virtual Meeting, June 11-15, 2021

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