Introduction
An anorectal fistula (ARF) is an epithelialized track that connects anorectum to skin
secondary to drainage or rupture of anal gland abscess.[1],[2] The true prevalence of anal fistulas is unknown with incidence of an ARF developing
from an anal abscess ranges from 26% to 38%.[3] The mean (range) age for presentation of ARF is 40 (20–60) years with twice as common
in men compared to women.[1] The common etiologies of ARF are anorectal abscess, Crohn's disease, lymphogranuloma
venereum, radiation proctitis, rectal foreign bodies, and actinomycosis. ARF is classified
in relationship to the anal sphincter and includes intersphincteric, transsphincteric,
suprasphincteric, and extrasphincteric fistulas.[1] Surgical management is the mainstay of therapy. The goal of surgical therapy is
to eradicate the fistula while preserving fecal continence.[4]
Adenocarcinoma in long-standing fistula-in-ano is a rare complication with no more
than 200 cases reported in literature. It accounts for 2%–3% of all large bowel carcinomas.[5] Due to chronic inflammation of ARF, early diagnosis of rare complication of malignancy
can be missed. The origin of fistula associated anal adenocarcinoma is debatable in
literature. The clinical hypothesis is that the rectal epithelial cells migrate into
the fistula and become malignant,[6] association with Crohn's disease,[7] or heterotopic intestinal cell rests.[8] We report a case of endoscopic ultrasound (EUS)-guided biopsy-proven adenocarcinoma
from long-standing fistulain-ano.
Case Report
A 70-year-old gentleman, without any addiction or comorbidities, diagnosed to have
fistula-in-ano for the past 40 years, presented with pus and mucus discharge for the
past 1 month. He underwent fistulectomy four times before reporting to our hospital.
The first surgery was at the age of 30 years with mucopurulent discharge per anus.
He had fistulectomy, but the disease recurred back after 5 years, and he underwent
redo-fistulectomy another three times for relapse of symptoms with the last surgery
being 10 years before the current presentation. He was evaluated in an earlier hospital
with normal colonoscopy and benign cells on the resected fistulous tract. He had recurrence
of mucopurulent discharge with rectal examination showing surgical scars, induration,
and mucopus from two external openings. Colonoscopy was performed for ruling out inflammatory
bowel disease, which was negative for the same [Figure 1]. Sonofistulogram and magnetic resonance imaging of the anorectal region revealed
complex perianal fistula with intrinsic frond like-polypoid enhancing mass [Figure 2]. EUS was performed using a Pentax linear echoendoscope - EG-3870 UTK connected to
a Hitachi Avius estiva ultrasound machine (2012). EUS showed a heterogeneous mass
of 3.4 cm × 2.9 cm size with cystic spaces in anorectum. EUS-guided fine-needle aspiration
cytology and fine-needle aspiration biopsy [Figure 3] were performed using a Wilson-Cook 22-gauge fine-needle aspiration needle. Cytology
and microhistology revealed moderately differentiated mucinous adenocarcinoma [Figure 4]. In view of large tumor and age of the patient, he was initiated on chemoradiation
to reduce the size of the tumor.
Figure 1: Colonoscopy image showing normal rectal mucosa without any intraluminal tumor
Figure 2: T2-weighted magnetic resonance imaging images showing complex perianal fistula with
intrinsic frond-like polypoid enhancing mass. Black long arrows indicate multiple
external openings, black short arrow showing one of the tracts, short white arrows
showing mass, and long white arrow showing an internal opening in between internal
and external sphincter
Figure 3: Endoscopic ultrasound image showing 5.1 cm × 2.2 cm heteroechoic mass with solid
and cystic areas till 7 cm starting from anal verge and transanal fine-needle aspiration
biopsy using a 22-guage Wilson-Cook needle
Figure 4: Histopathology photograph showing dilated tortuous glands with lakes of mucin and
intervening stroma showing desmoplastic reaction with lymphoplasmacytic infiltration
consistent with mucinous adenocarcinoma
A diagnosis of anorectal carcinoma arising from a former fistula requires not only
pathological findings but also knowledge of the clinical course of the patient. For
a malignant change to occur in ARF, it should be long standing, without tumor inside
anal canal or rectum, and internal opening of fistula in anal canal or rectum should
not contain malignant cells.[9] Five clinical features have been reported necessary for a diagnosis of anorectal
cancer arising from a fistula: (1) an anal fistula with continuous inflammation for
more than 10 years, (2) pain or induration of the anal fistula, (3) mucinous secretions,
(4) no evidence of any other primary cancer, and (5) the primary opening being an
anal crypt or the anal canal, but etiological relationship lacks surety because of
the rarity of the disease.[5]
Mucinous adenocarcinoma of the perianal region oscillates between the pathogenesis
of anal and rectal carcinomas causing a diagnostic and therapeutic uncertainty. A
high degree of clinical suspicion and histopathological confirmation is required to
identify and diagnose.[10] EUS can aid in evaluation of complex fistula-in-ano and ProCore biopsy for excluding
malignancy in suspected cases. To our knowledge, this is the first case in literature
of EUS confirmed adenocarcinoma arising from fistula-in-ano.
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Nil.
