Keywords
carcinoma prostate - rectal metastases -
18F-PSMA-1007 PET/CT
Introduction
Rectal metastases in prostate cancer are rare. Most patients with rectal involvement show rectal involvement by direct extension of the primary cancer. Isolated metastases to rectum that is noncontiguous with the primary tumor are rare. Isolated rectal metastases have diagnostic as well as prognostic implications. Isolated rectal metastases should be differentiated from primary rectal carcinoma. Also, whether isolated rectal metastases confer poor prognosis is debatable.
Case History
A 66-year-old male presented with complaints of bleeding per rectum, dysuria, retention of urine, and passage of urine from anal region. Cystoscopy and biopsy revealed adenocarcinoma prostate (Gleason score 4 + 4) following which patient underwent transurethral resection of prostate and suprapubic cystostomy. Fluorine-18 prostate specific membrane antigen (18F-PSMA-1007) positron emission tomography/computed tomography (PET/CT) was done for staging. The whole body 18F-PSMA-1007 PET/CT ([Fig. 1A]) shows multiple foci of abnormal tracer uptake in the pelvis and abdomen. The cross-sectional fused PET/CT and contrast-enhanced computed tomography (CECT) images showed increased uptake of radiotracer in primary tumor in residual prostate gland infiltrating the neck of urinary bladder, rectum, levator ani, and obturator muscles along with pelvic lymphadenopathy ([Fig. 1B, C]). An isolated PSMA avid enhancing nodule was also noted in the mucosal aspect of anterolateral wall of rectum away from the primary lesion ([Fig. 1D–G]).
Fig. 1 The maximum intensity projection image of whole-body Fluorine-18 prostate specific membrane antigen positron emission tomography/computed tomography (18F-PSMA-1007 PET/CT) (A) shows multiple foci of abnormal tracer uptake in the pelvis and abdomen. The transaxial fused PET/CT and contrast-enhanced computed tomography images showed increased uptake of radiotracer in primary tumor in prostate infiltrating the neck of urinary bladder, rectum, levator ani, and obturator muscles along with pelvic lymphadenopathy (B, C). An isolated PSMA avid enhancing nodule was also noted in the mucosal aspect of anterolateral wall of rectum away from the primary lesion in transaxial (D, E; black arrows) and sagittal (F, G; black arrows) sections.
Patient received six cycles of docetaxel-based chemotherapy along with androgen deprivation treatment. The maximum intensity projection image of whole body 18F-PSMA-1007 PET/CT post six cycles of chemotherapy ([Fig. 2A]) shows persistent radiotracer uptake in the primary and pre-existing metastatic sites in pelvis along with new foci of PSMA uptake. The transaxial fused PET/CT and CECT images showed persistent uptake of radiotracer in the previously documented nodular deposit in rectum ([Fig. 2B, C]). A new PSMA avid hypodense lesion was visualized in the anterior wall of rectum ([Fig. 2D–G]).
Fig. 2 The maximum intensity projection image of whole-body fluorine-18 prostate specific membrane antigen positron emission tomography/computed tomography (18F-PSMA-1007 PET/CT) post six cycles of chemotherapy (A) shows persistent radiotracer uptake in the primary and pre-existing metastatic sites in pelvis along with new foci of PSMA uptake. The transaxial fused PET/CT and contrast-enhanced computed tomography images showed persistent uptake of radiotracer in the previously documented nodular deposit in rectum (B, C). A new PSMA avid hypodense lesion was visualized in the anterior wall of rectum on transaxial (D, E; white arrows) and sagittal (F, G; white arrows) sections.
Discussion
Rectum is one of the least commonly involved site by prostate cancer by direct invasion or metastasis despite its close proximity to the prostate gland with few cases reported in the literature.[1]
[2]
[3] This has been attributed to rectoprostatic (Denonvilliers') fascia between the prostate and anterior rectal wall, which works as a critical barrier to local extension of tumor.[4] The possible reasons for rectal involvement may be related to tumor de-differentiation, positive surgical margins, or collision tumor in the very rare situation. Solitary metastasis to rectum by carcinoma prostate is even rare and it may be due to shared common lymphatic drainage by prostate and rectum or by tumor seeding while performing a needle biopsy of the prostate.[5] Patients can present with abdominal pain, rectal bleeding, and fecal or urinary discharge from abnormal routes in cases of fistulous tract formation. Differentiating primary rectal cancer from rectal involvement by prostate cancer is essential since the treatment and prognosis of these two entities vary significantly.[6]
[7] Although majority of prostate cancers with rectal involvement present with metastatic disease, rectal involvement by prostate cancer does not necessarily predict a worse outcome in hormone treatment naïve patients.[8] However, prior hormone therapy and rectal bleeding could be independent poor prognostic factors in prostate cancer patients with rectal involvement.
