Keywords
metastatic prostate adenocarcinoma - inferior gluteal lymph node -
68Ga-PSMA-11 PET-CT
Introduction
Prostate cancer is one of the commonly encountered male cancers in the world.[1] The diagnosis is made with the help of transrectal ultrasound (TRUS)-guided biopsy
and serum prostate-specific antigen (PSA) levels.[2] Prostate cancer usually metastasizes to the regional lymph nodes such as pelvic
lymph nodes (external and internal iliac); however, the involvement of the inferior
gluteal lymph nodal group (part of internal iliac group) is quite uncommon. We herein
report an unusual and unique case of prostate adenocarcinoma with involvement of bilateral
inferior gluteal lymph nodes.
Case Report
A 42-year-old male with a medical history of tobacco chewing for 2 years and cigarette
smoking in the past 23 years, initially presented with lower urinary tract symptoms
(obstruction of urine flow). The patient had a Eastern Cooperative Oncological Group
(ECOG) performance status of 1. The computed tomography (CT) urography showed a 2.6 × 2.6 × 3.2 cm
ill-defined lesion in the prostate with loss of fat planes with the base of the urinary
bladder and few enlarged internal and external iliac lymph nodes. Serum PSA levels
at baseline were 40 ng/mL. A TRUS-guided biopsy of the prostatic lesion showed conventional
prostatic adenocarcinoma with a Gleason Score of 5 + 4 = 9, WHO Grade Group 5 with
no lympho-vascular invasion and no perineural invasion. Bone scan showed no evidence
of bone metastasis. Baseline 68gallium-prostate specific membrane antigen positron emission tomography/computed tomography
(68Ga-PSMA-11 PET/CT) scan showed prostate-specific membrane antigen (PSMA) expressing
prostate lesions with PSMA expressing bilateral external and internal iliac, common
iliac, and para-aortic lymphadenopathy. The patient was put on medical androgen deprivation
therapy and was planned for external beam radiotherapy. He received 12 cycles of injection
leuprolide for 3 months and defaulted due to the coronavirus disease (COVID-19) pandemic.
Follow-up evaluation at a later date showed a raised PSA level of 148.4 ng/mL and
68Ga-PSMA-11 PET/CT new onset PSMA expressing metastatic left supraclavicular node and
new PSMA expressing metastatic intermuscular deposits in the bilateral gluteal region
([Figs. 1] and [2]). The patient then underwent bilateral scrotal orchidectomy and was started on tablet
abiraterone acetate due to rising serum PSA levels.
Fig. 1 Maximum intensity projection of 68Ga-PSMA PET scan at baseline (A) and after follow-up after 3 years postdefaulting (B), showing new onset bilateral inferior gluteal lymph nodes and left supraclavicular
lymph nodes; baseline-fused PSMA PET/CT (D), CT (E), and PET (G) axial images showing tracer avid prostatic primary and no inferior gluteal lymphadenopathy.
Follow-up-fused PSMA PET/CT (D), CT (F), and PET (H) axial images showing progression of local involvement of prostatic primary with
new onset meso-rectal nodes and bilateral inferior gluteal lymphadenopathy.
Fig. 2 Axial T1 MRI (A), axial T2 MRI (B) and axial diffusion-weighted imaging MRI sequence (C) of inferior gluteal lymph node (marked in yellow).
Discussion
A review of literature revealed only one study report which detected enlarged inferior
gluteal lymph nodes in a single case of prostate cancer with the help of multi-parametric
magnetic resonance imaging).[3] To the best of our knowledge, ours is the only report of involvement of bilateral
inferior gluteal lymph nodes in a case of prostate carcinoma on 68Ga-PSMA-11 PET-CT.
Prostate cancer is the sixth leading cause of cancer death among men worldwide and
the fifth highest incidence rate among males in India in 2016.[4]
[5] In high-risk prostate cancer, 68Ga-PSMA-11 PET/CT is known to be a useful method for the detection of metastases.[6] Associated with the rise of prostate cancer, use of PSMA-PET/CT has been indicated
for staging in high-risk prostate cancer, response assessment after therapeutic interventions
in correlation with serum PSA levels, and evaluating biochemical recurrence and prior
to planning patients for 177Lu-PSMA-617 therapy.[6] Prostate cancer follows a predominant hematogenous mode of spread to bones via prostatic
venous plexus draining into the vertebral veins and lymphatic mode to loco-regional
lymph nodes.[7] The process of metastasis can be outlined through five key stages: (1) penetration
of the basement membrane and movement into nearby tissue; (2) entry into either the
bloodstream or lymphatic system; (3) survival while circulating within these systems;
(4) exit from the vessels into tissue; and (5) establishment and growth of metastatic
growths in secondary locations.[8]
The posterior lobe of the prostate is drained via three primary pathways: (1) a lateral
pathway draining to the external iliac lymph nodes. These lymph vessels also drain
the terminal portion of the ductus deferens and seminal glands; (2) a laterodorsal
pathway, which drains into the internal iliac nodes, via a course following the prostatic
artery, and (3) a dorsal pathway, which drains to the sacral lymph nodes as well as
the promontories and common iliac lymph nodes. The lymphatics drained from the anterior
lobe of the prostate can be traced via two routes: (1) the majority of lymph drained
from the anterior surface proceeds to the external iliac lymph nodes, via the paravesical
space and (2) some vessels from the anterior lobe leave the prostate from the posterior
surface, draining into a group of nodes known as inferior gluteal lymph nodes, which
are part of the internal iliac lymph nodes. While the internal, external iliac, and
obturator lymph nodes are the most frequently involved in prostate carcinoma, metastases
to presacral and common iliac lymph nodes are relatively uncommon. The inferior gluteal
nodes are located along the inferior gluteal artery and drain the prostate and the
upper part of the urethra.
Albeit it is common to encounter loco-regional nodal disease, it is rare to detect
the involvement of inferior gluteal lymph nodes in a case of metastatic prostate carcinoma.
The gluteal lymph nodes belong to the parietal section of the internal iliac nodes.
They can be categorized into two subdivisions: superior and inferior gluteal lymph
nodes. These nodes are positioned alongside the corresponding blood vessels. These
lymph nodes collect lymph from the deeper regions of the pelvis, including the gluteal
subfascial and visceral tissues. The collected lymph subsequently flows into the internal
and common iliac nodes before progressing to the lateral caval lumbar nodes.[3]
A therapeutic implication to this may be that these nodes likely fall beyond the range
covered by radiation beams and are not easily reachable through standard surgical
procedures. As a result, they could have an impact on the way patients are clinically
treated and on their prognosis.
This patient also had simultaneous involvement of left supra-clavicular lymph node
and was detected on 68Ga-PSMA-11 PET/CT and is frequently related to disseminated disease.[6] A potential explanation for the involvement of left supraclavicular lymph nodes
is their proximity to the point where the thoracic duct enters the left subclavian
vein. This close positioning could facilitate the possibility of retrograde spread
allowing cancer cells to move against the natural flow of lymphatic drainage and reach
these nodes.[9]
Conclusion
Bilateral inferior gluteal nodal metastasis is a rare phenomenon that may have an
important implication for treatment planning and prognosis. The preferred imaging
method is either a pelvic MRI or 68Ga-PSMA-11 PET/CT. Their presence may alter the therapeutic radiation field coverage
in cases where external radiotherapy is advocated modality of choice and, thus, appropriate
detection may help in the correct management of the disease.
