Abdomen and Oncology

Key images

Findings

71-year-old male presented with ocular melanoma, increase in number and size of cystic liver lesions on abdominal ultrasound, evaluation with spectral CT.

Demonstration of iodine content of a gallbladder lesion quantitatively by iodine density and Z effective images. Better demonstration and delineation of gallbladder and small liver mass with virtual monoenergetic images at lower keV and iodine overlay images.

Axial and coronal images

Ultrasound showed increase in number and size of cystic liver lesions compared to previous imaging and sludge-like echogenicity in gallbladder. CT evaluation demonstrated an enhancing nodular lesion in gallbladder with HU values of 38 and 82.9 on true noncontrast and arterial phase images respectively. Virtual non-contrast images also showed similar HU (39.6 HU) to true non-contrast images. Iodine density and Z effective images demonstrated iodine uptake of the lesion. Virtual monoenergetic images at 40 keV and iodine overlay images allowed better delineation of the gallbladder mass and a small liver mass which was subtle on conventional images. PET/CT demonstrated high metabolic activity within the gallbladder mass (SUVmax 8.7). The lesion was found highly suspicious of melanoma metastasis. The patient underwent surgical biopsy and liver lesions were confirmed as melanoma metastasis. The patient was treated with immunotherapy and chemotherapy, however, follow-up CT showed progressive disease with increase of size of liver and gallbladder lesions.

Discussion

Spectral CT has the ability to quantitatively determinate the iodine content of a solid gallbladder mass. Virtual monoenergetic images at lower keV and iodine overlay images allow better demonstration and delineation of solid gallbladder mass and small liver metastasis with higher contrast.

(a) Conventional axial CT image without contrast: Gallbladder lesion (arrow) with an attenuation value of 38 HU. (b) Conventional axial CT arterial phase image: Contrast uptake of the lesion (82.9 HU, white arrow) and small subtle liver mass (blue arrow).

(c) Virtual non-contrast image: Gallbladder lesion (white arrow) with a similar attenuation value (39.6 HU) to true non-contrast image (38 HU). (d) Virtual monoenergetic image at 40 keV, arterial phase: Gallbladder (white arrow) and liver mass (blue arrow) are both more prominent.

Iodine overlay axial image: Gallbladder (white arrow) and small liver mass (blue arrow) with higher iodine content are more prominent.

Iodine density coronal images, arterial phase: Higher iodine content of the gallbladder mass (1.66 mg/ml, white arrow), compared to adjacent normal appearing liver parenchyma (0.09 mg/ml, blue arrow).

Z effective coronal images, arterial phase: Higher effective atomic number of the gallbladder mass (8.37, white arrow) color coded in green compared to adjacent normal appearing liver parenchyma (7.38, blue arrow) color coded in yellow.

PET/CT coronal images: High metabolic activity within the gallbladder mass (SUVmax 8.7, arrows).

Follow-up conventional CT 9 months later, axial image, arterial phase: Progression of the disease with enlargement of the gallbladder mass (arrow).