Asymptomatic Appendiceal Metastasis From Prostate Cancer Mimicking Metastatic Lymph Node as Solitary Disease on PSMA PET/CT Scan: The First Reported Case of Presurgical Diagnosis and Review of Literature

Metastasis of prostate cancer to the appendix is exceedingly rare. We can find only 11 cases reported in the world English literature. Their diagnoses were made postoperatively after presenting symptoms of appendicitis and at the time of surgery; many were found to have complicated appendicitis. We are reporting a new case of this rare disease with the diagnosis being made preoperatively, in absence of the symptoms. The follow-up prostate-specific membrane antigen (PSMA) PET/CT scan revealed a solitary abnormal finding at the medial right common iliac lymph node (LN) area and was interpreted as an LN metastasis. On CT simulation for radiation treatment (RT) planning, however, it was noted that this lesion drifted slightly away from the location of the LN. A spot of calcification was noted within this lesion. The CT scan of lower abdomen confirmed that this lesion, size 1.2 × 0.8 cm, was indeed located in the appendix. Considering the high risk of geographic missing of this small mobile lesion, which could result in underdosage and slow response of prostate cancer to RT, this led to changing the treatment to surgical resection. The appendectomy confirmed histological appendiceal metastasis of prostate cancer and presence of appendicolith in the lumen which was dilated distally and contained purulent material. The wall thickness ranged from 0.1 to 0.4 cm. Our case is different from all the previously reported cases in that the disease was solitary, and the diagnosis was made clinically prior to the surgery. This early detection and early surgical treatment likely prevented severe complicated appendicitis associated with prolonged duration of inflammation and appendicolith. The surgical approach avoided adverse effects of radiation to the bowel.