Case Presentation A 40-year-old female patient with no prior comorbidities, in good nutritional status,
underwent a screening colonoscopy due to a family history of colorectal cancer. An
LST (laterally spreading tumor) was found in the ascending colon, near the cecum.
The lesion was elevated with saline solution and endoscopic mucosal resection (EMR)
was performed using a diathermic loop in a piecemeal fashion, without complications
during the procedure. On the 15th post-procedure day, the patient developed an increase
in abdominal volume in the hypogastric region, which was painless. She did not present
with fever, leukocytosis, or any systemic or intestinal symptoms, but had a significant
abdominal bulging with a palpable mass. A CT scan revealed an expansile formation
with thin walls and gas content in the right iliac fossa, medial to the ascending
colon, causing an impression on the abdominal wall. After no resolution with conservative
treatment, the patient underwent a videolaparoscopy on the 20th day post-mucosectomy,
which revealed a loculated retroperitoneal pneumoperitoneum, with no apparent perforation
or colon injury. A puncture was performed on the bulging area, releasing a significant
amount of gas, with no signs of enteric fluid or feces, and the posterior peritoneum
was opened by approximately 1 cm, where the gas encapsulation was located. On the
15th post-operative day following VLP (videolaparoscopy), the patient returned to
the outpatient clinic with a similar painless abdominal volume increase, and imaging
studies showed compatible findings. A decision was made for a laparotomy through a
transumbilical incision, with findings similar to the previous VLP: a large encapsulated
retroperitoneal pneumoperitoneum with only gas inside, again with no apparent perforation
or colon injury. A careful and extensive dissection of the peritoneal wall was carried
out, and the cavity was drained. The patient progressed well, with resolution of the
condition and late post-operative imaging showing no significant findings. The pathological
examination of the LST confirmed it as a tubular-villous adenoma.
Discussion Endoscopic mucosal resection (EMR) is a procedure used to remove early-stage precancerous
lesions or other abnormal tissues from the gastrointestinal tract. Mucosectomy for
LST is a safe and effective technique for treating sessile and flat lesions in the
colon, with low recurrence or complication rates, though it occasionally results in
piecemeal excision for larger lesions. This case represents a peculiar and atypical
post-mucosectomy complication, with few similar cases described in the literature.
