Tc99m-MDP uptake in ascitic fluid in a patient with prostate carcinoma: A clue to detect metastases.

Bone scintigraphy with Tc-99m methylene diphosphonate (MDP) is used to detect metastases in patients with cancer. Uptake in non-osseous, non-urologic tissues is occasionally found in the routine bone scintigraphy, which may mimic as metastatic lesions. The authors describe the case of a 70-year-old man with prostate cancer, showing diffuse tracer uptake in the left hemithorax and entire abdomen on bone scan that required additional imaging modality for localization. Careful interpretation is needed of the unusual uptake of radiotracer in regions other than the skeleton for metastatic work up.

INTRODUCTION

Most common sites of metastatic disease in prostate cancer are bones, lymph nodes, and lungs. Malignant pleural or peritoneal effusions are extremely rare. Abdominal and/or pleural cavity spread is manifestation of advanced malignant disease and is associated with a poor prognosis. Tc99m bone scintigraphy used to detect bone metastasis may show uptake in non-osseous, non-urologic tissues also representing metastatic lesions

CASE REPORT

A 70-year-old man of carcinoma prostate with rising prostate specific antigen (PSA) was subjected to bone scan for the assessment of possible metastatic bone disease. Contrast-enhanced computed tomography (CECT) demonstrated enlarged prostate with periprostatic infiltration. Tc-99m methylene diphosphonate (MDP) bone scan showed abnormal radiotracer uptake in the abdomen and left hemithorax, not corresponding to the skeleton [Figures 1a and b]. Single-photon emission computed tomography (SPECT)/CT images of abdomen [Figure 1c] and thorax [Figure 1d] localized increased tracer uptake to the pleural and ascitic fluid, respectively.

Figure 1

Whole body Tc-99m MDP bone scan (a) anterior and (b) posterior view showing abnormal radiotracer uptake in the abdomen and left hemithorax, which does not correspond to any part of the skeleton. SPECT/CT images of abdomen (c) and thorax (d) localize increased tracer uptake to the ascitic and pleural fluid, respectively

DISCUSSION

Carcinoma of the prostate is predominantly a tumor of older men. It can metastasize to nearly every organ, but metastasis without bone involvement is rare. Most common sites of metastatic disease are bones, lymph nodes, and lungs. Uncommon sites of metastatic disease include adrenal gland, kidney, brain, pancreas, genitalia, and breasts. Malignant effusions, whether pleural or peritoneal, are extremely rare.[1] Abdominal cavity spread was documented by Hess et al. in 3 of 316 metastatic prostate cancer patients, mostly in conjunction with skeletal and nodal spread.[2] Broghamer et al. described a series of 33 patients with carcinoma of prostate and the ascites.[3] It is a manifestation of advanced malignant disease and is associated with a poor prognosis.

Ultrasound is reliable in the detection of ascites, being able to detect as little as 100 mL of fluid in the peritoneal cavity.[4] CT and MRI are also effective at detecting ascites.[5] A positive cytology result confirms a malignant etiology in ascites and is extremely specific.[6] Increased Tc-99m MDP uptake in extra-osseous sites, including pleural and pericardial effusion, is also reported in the literature.[7] It is due to extracellular fluid expansion, enhanced regional vascularity and permeability, and elevated tissue calcium concentration. The composition of the calcium deposition and the presence of other metallic ions (e.g. iron and magnesium) are also important. Neoplastic, hormonal, inflammatory, ischemic, traumatic, excretory and artifactual causes have been demonstrated to account for the extra-osseous Tc-99mTc MDP uptake.[8] Recognition of the pathophysiologic basis underlying ascetic fluid MDP uptake can enhance the interpretation and diagnostic value of bone scintigraphy. Use of SPECT/CT helps in precise localization of the diffuse tracer uptake.

In the present case, the patient underwent bone scintigraphy that did not show skeletal metastases. However, the diffuse abdominal and left hemithorax uptake may be due to malignant effusion. To further elucidate the tracer uptake in that region, additional SPECT/CT was taken which showed localization of tracer uptake to the ascitic and pleural fluid. Ascitic fluid cytology subsequently revealed metastatic adenocarcinoma. The unusual presentation illustrates metastatic involvement without skeletal pathology that may be present in scintigraphic bone imaging.