1) MRI is the preferred imaging modality for staging anal carcinoma due to its ability to accurately assess the size and extent of primary tumors as well as lymph node involvement. 2) Anal carcinoma is typically staged according to tumor size (T-stage), lymph node involvement (N-stage), and presence of distant metastases (M-stage). MRI allows for evaluation of these factors. 3) Additional imaging with PET/CT may be used to detect distant metastases and better define lymph node involvement, potentially changing staging in 20% of cases and treatment planning in 3-5% of cases.

1. Radiological Imaging of Anal Carcinoma.
Dr/ ABD ALLAH NAZEER. MD.

2. Normal Anatomy:
The anal canal begins at the narrowing of the rectal ampulla at the
anorectal junction where the rectum enters the puborectalis sling at the
apex of the anal sphincter complex. It extends distally for approximately
4 cm and ends at the anal verge where the squamous mucosa blends with
the perianal skin. The anal margin is the circular rim of pigmented skin
with folds surrounding the anus, extending over an approximately 5-cm
radius away from the anal verge. The most significant landmark of the
anal canal is the dentate line, which lies 2.5–3 cm proximal to the anal
verge and is visible macroscopically but not on MRI. Its position can be
estimated either by measuring 2.5 cm above the anal verge or by dividing
the anal canal into thirds so that the dentate line lies at the junction of the
middle and upper thirds. The anal canal is divided by the dentate line into
an upper part, lined with transitional or rectal glandular mucosa, and a
lower part, lined by nonkeratinizing squamous epithelium, that merges
with the perianal skin. The anal transition zone is defined as the histologic
zone interposed between uniform rectal glandular mucosa above and
uninterrupted squamous epithelium below, and it often has a
heterogeneous histologic appearance.

3. Illustrative anatomy of anal canal.
A, Line diagram shows anal anatomy.
B, Healthy 67-year-old man (with treated prostate
cancer).Coronal T2-weighted image that
corresponds to A shows ischioanal fossa (IAF),
external sphincter (ES), and internal sphincter (IS).

4. C, Healthy 53-year-old woman (with treated
carcinoma cervix). Axial T2-weighted image through
upper anal canal shows urethra (Ur) and vagina (Va).
D, 67-year-old woman (post TAH and BSO for endometrial
sarcoma). Sagittal T2-weighted image shows pubococcygeal line
(long straight line), which is generally at level of anorectal junction.
Angled line shows reference plane that one should use when
reporting distance of epicenter of abnormality from anal verge.

5. Anal cancer is a relatively uncommon malignancy. It accounts for
less than 2% of large bowel malignancies and 1-6% of anorectal
tumours (~1.5% of all gastro-intestinal tract malignancies in the
Unites States).
Epidemiology
There may be a slight male predilection where its incidence has been
reported to be approximately 0.5 per 100 000 in men and 1.0 per
100 000 in women. Its incidence is thought to be rising over the
years.
Clinical presentation
Approximately 45% of patients may present with bleeding per
rectum. Around 30% of patients may have pain and/or a sensation
of a mass.
Pathology
Anal carcinoma typically originates between
the anorectal junction above and the anal verge below. The vast
majority of anal canal cancers are squamous cell cancers.

6. Risk factors
Both male and female:
HPV / HIV infection
immunosuppression
number of lifetime sexual partners, and receptive anal
intercourse
smoking
In females: previous in situ or invasive cervical, vulval or
vaginal cancer.
Lymphatic spread
tumour above dentate line: to pararectal and
paravertebral nodes
tumour below dentate line: to inguinal and femoral nodes

7. The accepted TNM staging of anal cancer is as follows:
Primary tumour (T)
TX: primary tumour cannot be assessed
T0: no evidence of primary tumour
Tis: carcinoma in situ
T1: tumour 2 cm or less in greatest dimension
T2: tumour >2 cm but <5 cm in greatest dimension
T3: tumour >5 cm in greatest dimension
T4: tumour of any size invades adjacent organ(s), e.g. vagina, urethra, bladder
Regional lymph nodes (N)
Nx: regional lymph nodes cannot be assessed
N0: no regional lymph node metastasis
N1: metastasis in perirectal lymph nodes(s)
N2: metastasis in unilateral internal iliac and/or inguinal lymph node(s)
N3: metastasis in perirectal and inguinal lymph nodes and/or bilateral internal
iliac lymph nodes
Distant metastasis (M)
Mx: distant metastasis cannot be assessed
M0: no distant metastasis
M1: distant metastasis

8. Radiologic staging is supplemented by clinical assessment of the
anal margin, verge, and canal. This assessment often involves an
examination with the patient under anesthesia and biopsy.
Biopsy or fine-needle aspiration cytology of any enlarged or
suspicious-appearing inguinal nodes is also essential.
Transanal Endoscopic Ultrasound Transanal endoscopic
ultrasound has results comparable to MRI for the detection of
local tumor spread in patients with anal carcinoma and may be
superior to MRI for the detection of small superficial tumors.
However, regional lymph nodes higher in the pelvis or groins are
outside the FOV of endosonography and supplementary MRI is
needed for N staging. A meta-analysis of staging rectal cancer
using endorectal ultrasound revealed other limitations including
operator dependency and inability to assess stenotic tumors ;
these limitations likely apply equally to anal cancer.

9. MRI
MRI has become the imaging modality of choice for locoregional staging and
assessment of tumor response after chemoradiotherapy. MRI provides high-resolution
multiplanar information about the location, size, circumferential and craniocaudal
extent of the primary tumor and information regarding the involvement of adjacent
structures.
There is no significant difference in diagnostic value between pelvic surface coils and
endoluminal coils. Moreover, endoluminal coil imaging is limited by a narrow FOV and
near-field artifact and may not be tolerated by patients with anal cancer. MRI with a
pelvic surface coil is easy, is more acceptable to the patient, and shows both local
spread of the disease as well as lymph node involvement.
We routinely perform MRI of anal cancers with a standard technique using a body coil;
we obtain transaxial T1-weighted images with a 5-mm slice thickness to cover the
abdomen and pelvis. High-resolution thin-section T2-weighted images are obtained
with a 3-mm slice thickness in three orthogonal planes through the anal canal using a
pelvic surface coil. In our experience, contrast-enhanced MRI offers limited advantages
over standard T2-weighted sequences in routine primary staging but can be helpful to
assess fistulation to other organs. Fat-suppressed imaging can help improve the
conspicuity of the primary tumor, and STIR sequences are also useful to show fistula
tracks. Diffusion-weighted imaging has an emerging role, particularly for detection of
recurrent tumor after therapy, and can aid in differentiation of suspected residual or
recurrent tumor from treatment-related change.

10. 8F-FDG PET/CT
FDG PET/CT has an increasing role in staging and treatment
planning of anal carcinoma, particularly because up to 98% of anal
tumors are FDG-avid. At diagnosis, FDG PET/CT is used to evaluate
primary tumor size, lymph node status, and whether distant
metastases are present. FDG PET/CT can also be useful for planning
radiation therapy by clearly defining sites of metabolically active
tumor. Several studies have shown that FDG PET/CT (in comparison
with standard imaging) alters staging of anal carcinoma in
approximately 20% of cases and treatment intent in approximately
3–5% of cases. Although PET/CT has a lower sensitivity in detecting
perirectal nodes than MRI, this shortcoming does not affect
management because perirectal nodes are routinely irradiated.
The main impact of PET/CT on therapy stems from its superiority in
detecting involved pelvic or inguinal lymph nodes, provoking the
radiation oncologist to include them in the radiotherapy field.

11. T staging of rectal cancer according to depth of tumor invasion as seen on axial T2-weighted MR images. (a) T1 cancers invade
the submucosa (arrows) but do not involve the muscularis propria. (b) T2 cancers invade the muscularis propria but do not
reach the subserosa (arrow). (c) T3 cancers invade beyond the muscularis propria (arrow). (d) T4 cancers invade through the
serosal covering (T4a) or another fascial plane (T4b) and/or involve an adjacent organ (T4b) (arrows).

12. A 32-year-old HIV-positive woman with clinical diagnosis of anovaginal fistula. Axial T2-weighted
(a) and post-contrast fat-suppressed axial T1-weighted (b) images show inhomogeneous anal
tissue invading the left aspect of the vagina (arrowheads), with internal non-enhancing necrosis
and peripheral enhancement. Biopsy diagnosed SCAC with superimposed infection

13. Early anal tumour, MR image shows that normal low
signal of anal canal muscle has been replaced by
intermediate-signal tumor (arrow) that is less than 2 cm.
Early anal carcinoma, anterior T2 anal canal
carcinoma. MR image shows that lesion measures
more than 2 cm and hence achieves T2 status.
There is invasion of external sphincter (arrow).

14. A 40-year-old MSM with bioptic diagnosis of SCAC. Axial (a) and sagittal (b) T2-weighted images show
2-cm hyperintense nodule contained within the internal sphincter muscle, intensely enhancing as seen
on post-contrast fat-suppressed coronal T1-weighted image (c), consistent with T1 tumour (arrowheads).

15. A 62-year-old female with biopsy-proven SCAC. Axial T2-weighted (a), post-contrast fat-suppressed axial
(b) and coronal (c) T1-weighted images, and corresponding enhanced image from body CT (d) show a 5.5-
cm long (T3) enhancing tumour with infiltration of the left ischioanal fatty space (arrowheads).

16. A 57-year-old woman undergoing abdomino-pelvic MDCT for unrelated reasons. Post-contrast axial (a) and
coronal reformatted (b) detailed images of the anorectal region identify an unexpected 2-cm right-sided
enhancing anal nodule. Subsequent clinical and bioptic assessment confirmed poorly symptomatic ulcerated SCAC.

17. 46-year-old man with T3 anal carcinoma. A, Coronal T2-
weighted image shows that neoplasm (bracket) extends from
anal margin into lower rectum and is more than 5 cm in
maximum dimension and therefore is T3. There is invasion
of external sphincter and of left levator ani muscle (arrow).
46-year-old man with T3 anal carcinoma. B, MR
image shows no evidence of adjacent organ invasion,
as evidenced by complete low-signal rim (arrowheads)
separating tumor from prostate anteriorly.

18. Axial contrast-enhanced MR images in a patient with stage IIIB (cT3N2M0) adenocarcinoma of the
rectum. (a) Image shows a low rectal mass with a small focus of extension into the adjacent mesorectal fat
(arrow) (T3 disease). (b, c) Multiple enhancing subcentimeter mesorectal lymph nodes (arrows in b) and a left
internal iliac lymph node (arrow in c) suggest N2 disease on the basis of the number of potentially involved lymph
nodes. The patient subsequently underwent neoadjuvant chemotherapy and radiation therapy and resection.

19. Stage IIIB (cT3N2M0) squamous cell carcinoma of the anus. (a, b) Coronal CT images obtained at different levels show a locally
extensive mass extending superiorly from the anorectal junction (arrows in a). Pathologic analysis demonstrated squamous cell
carcinoma consistent with anal cancer, despite the relatively superior location. A prominent left internal iliac lymph node is
also seen (arrow in b). (c, d) Coronal CT images obtained at different levels 3 months after completion of definitive
chemoradiation therapy show a partial radiographic response of both the primary mass and the left internal iliac lymph node.

20. An elderly, 92-year-old man with previous prostatectomy and kidney failure has unenhanced MRI.
Sagittal T2- (a) and axial T1-weighted (b) images show 5-cm long solid, inhomogeneous neoplastic
tissue (*) extending from the anus to encase the proximal urethra (note catheter in place).

21. A 65-year-old woman with history of previously treated small SCAC 3 years earlier. Axial T2- (a) and post-contrast
T1-weighted (b) images show roundish 1-cm left inguinal node (arrowheads) with internal fluid-like necrosis and
inhomogeneous enhancement, confirmed by ultrasound (c) as hypoechoic with loss of normal nodal structure.
Surgical exeresis (postoperative status as seen in d, follow-up MRI) confirmed metastatic node from SCAC.

22. Axial T2-weighted (a, b) and post-contrast fat-suppressed T1-weighted (c) images show inguinal nodal
metastases, larger on left side (arrowheads) plus bilateral enhancing perirectal adenopathies (arrows)

23. 35-year-old woman with T4 anal cancer. MR image shows lobulated
tumor with central necrosis and invasion into posterior vagina (arrow).

24. Axial fused FDG PET/CT images of 45-
year-old man with upper anal cancer.
A, Bulky anal cancer shows increased
FDG uptake (arrow) and metabolically
active right inguinal node (arrowhead).
Axial fused FDG PET/CT images of
45-year-old man with upper anal
cancer. B, Increased uptake in pelvic
sidewall lymph node (arrowhead) is
consistent with disease involvement.
Axial fused FDG PET/CT images of 45-year-
old man with upper anal cancer.
C, Increased uptake in unsuspected liver
lesion (arrowhead) was subsequently
shown to be metastasis on liver MRI (not
shown). Ability of FDG PET/CT to stage
regional and metastatic disease accurately
in single examination is its great strength

25. A, Coronal T2-weighted MR image shows bulky
T3 tumor in upper anal canal (arrow) that was
subsequently treated with chemoradiotherapy.
Coronal T2-weighted image obtained 8 weeks after therapy
shows that tumor has diminished in size and there is tram-track
appearance of low-signal fibrotic tissue encasing anal canal wall
(arrowhead). Note that mass like pseudotumor of high signal in
rectal mucosa (arrow) is edema from radiotherapy.

26. 37-year-old man with bulky T3 anal cancer. A, Axial
T2-weighted MR image obtained before treatment.
37-year-old man with bulky T3 anal cancer. B, Axial T2-
weighted image obtained 3 months after therapy depicts
low-signal fibrosis in place of tumor (arrow). Patient had
complete response clinically and radiologically.

27. A, T2-weighted MR image obtained
at time of initial staging shows
abnormal tumor tissue in lower
anal canal, which was treated with
chemoradiotherapy.
B, T2-weighted MR image obtained 8
weeks after therapy shows significant
size reduction and fibrotic reaction,
but residual nodule (arrow)
suspicious for remnant tumor is seen.
C, Repeat T2-weighted MR image obtained
immediately before resection shows
nodule (arrow) has enlarged compared to
initial post treatment (B). This nodule was
confirmed to be tumor at histology after
salvage abdominoperineal resection.

28. A, Coronal T2-weighted MR
image shows small tumor
involving lower anal canal and
anal margin (arrow) that was
treated with chemoradiotherapy
with good initial response
B, Coronal MR image obtained
for surveillance 1 year after
chemoradiotherapy shows
intermediate- to high-signal
abnormality (arrow) suspicious
for recurrent tumor at site of
original primary.
C, Axial T2-weighted MR image
from same examination as B shows
areas of small-volume, linear post-
therapy fibrosis (arrowhead) and
bulky intermediate- to high-signal
abnormality (arrow) suspicious for
recurrence.
D, Apparent diffusion
coefficient map from diffusion-
weighted imaging series
shows rim of restricted
diffusion (arrow) in
intermediate T2 signal areas
indicative of high cellular
content.

29. A 60-year-old man with AIDS and clinical finding of ulcero-fungating anal mass. Axial (a) and coronal reformatted (b)
CT images show moderately heterogeneous tissue (*) in its entire longitudinal extent from the anorectal junction to
below the anal verge, associated with large necrotic iliac adenopathies (* in c). Biopsy confirmed super infected SCAC.

30. An 83-year-old man with known SCAC. Initial MRI shows moderate circumferential thickening of the anus with
T2-hyperintense signal (a) and contrast enhancement (b) (arrowheads). Complete disappearance of the lesion is
observed on axial T2 (c) and post-contrast fat-suppressed T1-weighted (d) images following chemo-radiotherapy.

31. An elderly, 85-year-old lady with biopsy-proven SCAC and multiple comorbidities. Initial MRI (a, b) shows showed
circumferential anal wall thickening with abnormal solid signal (arrowheads) measuring 6 cm in length, plus a suspicious
centimetric left inguinal lymph node (arrow in a), findings consistent with T3N2 lesion. After reduced chemo-radiotherapy,
follow-up MRI (c, d) 4 months later disclosed progression and partial necrosis of both primary tumour (arrowhead) and
inguinal adenopathy (arrow), plus appearance of an exophytic tissue mass protruding from the external anal orifice (* in d)

32. A 40-year-old male patient with long-standing perianal Crohn’s disease, being treated with seton.
Contrast-enhanced MDCT images (a, b, c in cranio-caudal order) show right-sided levator ani abscess (*),
extensive perianal fistulization occupying the ischioanal space (arrow), and marked solid-appearing
circumferential anorectal thickening (arrowheads). Abdomino-perineal resection for SCAC was performed

33. Image shows an HIV-positive 41-year-old male with squamous cell carcinoma of the anus. Pretreatment FDG-PET/CT (left)
demonstrated increased uptake in the anal canal (arrows) and a left internal iliac lymph node. Post-treatment FDG-PET/CT (right)
demonstrated persistent uptake in the anal canal and new activity in the right lobe of the liver (arrows). The patient had biopsy-
proven local and distant disease and died from local and metastatic disease 12 months after completion of chemoradiation.

34. Image shows a 47-year-old female with squamous cell carcinoma of the anus. Pretreatment FDG-PET/CT (left)
demonstrated increased uptake in the right anal canal and two 5-mm perirectal lymph nodes. Post-treatment FDG-PET/CT
(right) showed complete metabolic response. She remains without evidence of disease 31 months after chemoradiation.

35. Thank You.