Dear Editor,
I wish to contribute to the upcoming special issue on imaging in rectal cancer, focusing
on rectal gastrointestinal stromal tumors (GISTs). Although rare, rectal GISTs account
for approximately 5% of GISTs and present unique diagnostic challenges that can influence
treatment strategies. These tumors differ significantly from rectal adenocarcinomas
in origin, imaging features, and therapeutic approaches, necessitating increased awareness
among radiologists.
The cross-sectional imaging findings of rectal GISTs often include well-defined, noncircumferential,
and exophytically growing masses. On magnetic resonance imaging (MRI), these tumors
typically appear iso- to hypointense on T1-weighted images and hyperintense on T2-weighted
images, with enhancement patterns that vary depending on tumor size and internal composition.
Diffusion-weighted MRI is particularly valuable in characterizing tumor aggressiveness,
though findings may vary depending on the proportion of solid versus cystic components
within the lesion. Dynamic contrast-enhanced MRI further complements this by delineating
vascularity and internal architecture.[1]
Various studies also highlight the absence of lymphadenopathy and the frequent presence
of necrosis, hemorrhage, or cystic changes in large GISTs. These imaging hallmarks,
combined with fluorodeoxyglucose-positron emission tomography (FDG-PET) avidity, can
help differentiate GISTs from other mesenchymal tumors or rectal adenocarcinomas,
which are more likely to involve regional lymph nodes.[2] FDG-PET is particularly valuable in postoperative cases for identifying recurrence
and detecting other intra-abdominal deposits, ensuring timely management of metastatic
disease.
Accurate imaging is vital for the multidisciplinary management of rectal GISTs. Neoadjuvant
therapy with tyrosine kinase inhibitors, such as imatinib, is often employed to reduce
tumor size and facilitate surgical resection while preserving sphincter function.
Imaging plays a crucial role in monitoring therapeutic response and ensuring optimal
outcomes.[3]
As rectal GISTs are often underrecognized, incorporating these insights into imaging
protocols for rectal cancer can improve diagnostic accuracy and optimize patient outcomes.
I commend the editorial team for focusing on imaging in rectal cancer and hope this
letter underscores the importance of considering rare entities like rectal GISTs in
clinical practice ([Fig. 1]).
Fig. 1 A 46-year-old mass with rectal gastrointestinal stromal tumor (GIST). (A) Sagittal T2-weighted magnetic resonance (MR) image shows an exophytic predominantly
hyperintense mass (arrow) with cystic (long-thin arrow), hypointense areas and fluid–fluid
level (double-headed arrow) closely associated with and displacing the rectum. The
mass closely abuts the prostate without evidence of invasion. (B) Axial T1-weighted MR image shows hyperintense area within the mass (arrow), suggestive
of intratumoral hemorrhage. (C) Axial diffusion-weighted (DWI) MR image (b-value = 800) shows mixed high signal. (D) Coronal T2-weighted MR image shows the lesion displacing the rectum to the right.
Focal thinning of the wall is seen (arrow) indicating its origin. (E) Abdominal perineal resection specimen shows lobulated gastrointestinal stromal tumor
(arrow) arising from the rectum. Note the smooth rectal mucosa (double-headed arrows),
denoting submucosal origin of the tumor. (F) High-power image stained with hematoxylin and eosin shows that the tumor is composed
of fascicles of uniform spindle cells with elongated nuclei and palely eosinophilic
cytoplasm. Inset shows immunohistochemistry image showing diffuse positivity for KIT
(CD117). The tumor also showed diffuse positivity for DOG1 (not shown). (G) Two years later, the patient presented with pelvic recurrence. Fluorodeoxyglucose-positron
emission tomography (FDG-PET) computed tomography (CT) shows intense FDG avidity along
the peripheral solid component of the mass (arrow). (H) Contrast-enhanced CT scan of a 70-year-old man with rectal bleeding and severe anemia
shows gastrointestinal stromal tumor extending from the anterior rectal wall with
irregular and ulcerated intraluminal component (arrows).
Thank you for the opportunity to contribute. I would be delighted to discuss this
topic further or provide additional details if required.
