A computed tomographic (CT) image is a display of the anatomy of a thin slice
of the body developed from multiple x-ray absorption measurements made around
the periphery of the body. Unlike conventional tomography, where the image of
a thin section is created by blurring out the information from unwanted
regions, the CT image is constructed mathematically using data arising only
from the section of interest. Generating such an image is confined to cross
sections of the anatomy that are oriented essentially perpendicular to the
axial dimensions of the body. Reconstruction of the final image can be
accomplished in any plane.  
  
**Abdominal CT**  
  
The CT of the abdomen extends from the dome of the diaphragm to the pelvic
brim or pubic symphysis, depending upon whether one groups the pelvis with the
abdomen or treats it separately.  
  
A CT scan of the abdomen will be considered medically reasonable and necessary
under the following circumstances2:  
  
 Evaluation of abdominal pain3,8,9  
  
 Evaluation of known or suspected abdominal masses or fluid collections  
  
 Evaluation of primary or metastatic malignancies  
  
 Evaluation of abdominal inflammatory processes  
  
 Evaluation of abnormalities of abdominal vascular structures (Note: Medical
necessity for CT angiography is not addressed in this LCD)  
  
 Evaluation of abdominal trauma  
  
 Clarification of findings from other imaging studies of the abdomen or
laboratory abnormalities suggesting abdominal pathology  
  
 Guidance for interventional diagnostic or therapeutic procedures within the
abdomen  
  
 Treatment planning for radiation therapy  
  
 For patients being evaluated for potential transcatheter aortic valve
implantation/replacement (TAVI or TAVR) provided that the patient has not
undergone a CT of the abdomen within the preceding 60 days1,4,6  
  
 **Pelvic CT**  
  
The CT scan of the pelvic area includes all pelvic structures including the
bladder, the prostate in males, ovaries, uterus, and uterine adnexa in
females, and the lower retroperitoneum, and iliac lymph node chains. The CT
scan of the pelvis is useful in evaluating cysts, tumors, masses, metastases
to one or more of these organs, and iliac lymph nodes. Intravenous contrast
material may be administered.  
  
A CT scan of the pelvis will be considered medically necessary and reasonable
under the following circumstances2:  
  
 Evaluation of cysts, tumors, or masses of the pelvic structure (i.e., that
which lies at or below the pelvic brim or true pelvis)  
  
 Evaluation of metastasis of primary cancers to this region  
  
 Evaluation of inflammatory processes in this region  
  
 Evaluation of abnormalities of pelvic vascular structures  
  
 Evaluation of lymphadenopathies of this region  
  
 Evaluation of lower abdominal, generalized abdominal or pelvic pain3,8,9  
  
 Evaluation of other genitourinary (GU) disorders in which the physician
cannot make a diagnosis on physical examination and/or by ultrasound (US)  
  
 Evaluation of trauma to the pelvic structure/organs  
  
 Evaluation of the effectiveness of a radiation treatment plan  
  
 For patients being evaluated for potential TAVI or TAVR provided that the
patient has not undergone a CT of the pelvis within the preceding 60
days.1,4,6  
  
Intravenous contrast material may be administered with any of the above
studies.  
  
In addition to the medical necessity requirements, the CT scan must be
performed on a model of CT equipment that meets the following criteria:  
  
 The model must be known to the Food and Drug Administration (FDA); and  
  
 Must be in the full market release phase of development.

The American College of Radiology (ACR) (2016) published its practice
parameters for the performance of CT of the abdomen and pelvis.2 This
publication includes the indications for abdominal and/or pelvic CT
examinations. In 2018, Scheirey et al published the ACR Appropriateness
Criteria for nonlocalized abdominal pain.9 This review focused on imaging the
adult population with nonlocalized abdominal pain, including patients with
fever, recent abdominal surgery, or neutropenia. The authors concluded that
imaging of the entire abdomen and pelvis to evaluate for infectious or
inflammatory processes of the abdominal viscera and solid organs, abdominal
and pelvic neoplasms, and screen for ischemic or vascular etiologies is
essential for prompt diagnosis and treatment. The authors state that computed
tomography, which is often the first-line modality, quickly evaluates the
abdomen/pelvis, providing for accurate diagnoses and management of patients
with abdominal pain. Furthermore, while often performed, abdominal radiographs
may not alter management.

Haller et al (2010) performed a retrospective review to evaluate whether non-
contrast CT (NCT) provided more diagnostic information than abdominal plain
film (APF) in patients that presented with acute non-traumatic abdominal
pain.3  The authors also addressed if use of CT could reduce the total number
of additional radiograms. A total of 222 patients were retrospectively
reviewed. 86 patients had APF, 60 had standard-dose CT (SDCT), and 76 had low-
dose CT (LDCT). The radiological report of each patient was compared with the
final diagnosis obtained from the medical record within 30 days. Additional
radiograms were registered, and a total radiation dose excluding or including
APF or NCT was calculated. Results showed that NCT gave a correct diagnosis in
50% compared to 20% with APF (P < 0.001). The total number of additional
radiograms was substantially lower in the CT group compared to the APF group
(P < 0.001). In addition, the average sum of radiation dose was similar for
APF and LDCT. The authors concluded that NCT was significantly better at
providing diagnostic information when compared to AFP in patients presenting
with acute abdominal pain as well as reducing the number of additional
radiograms.

Pandharipande et al (2016) conducted a prospective study to determine how the
diagnoses, diagnostic uncertainty, and management decisions of physicians are
affected by the results of CT in the emergency department (ED).8 Physicians
were surveyed before and after CT to determine the leading diagnosis,
diagnostic confidence, alternative "rule out" diagnosis, and management
decisions. Primary measures were the proportion of patients for whom the
leading diagnosis or admission decision changed and median changes in
diagnostic confidence. Secondary measures addressed alternative diagnoses and
return-to-care visits (e.g., to emergency department) at 1-month follow-up.
The leading diagnosis changed in 235 of 460 patients with abdominal pain
(51%). Pre-CT diagnostic confidence was inversely associated with the
likelihood of a diagnostic change ( _P <_ 0.0001). Median post-CT confidence
was 95%. CT helped confirm or exclude at least 95% of alternative diagnoses.
Admission decisions changed in 116 of 457 patients with abdominal pain (25%).
During follow-up, 70 of 450 patients with abdominal pain (15%) returned for
the same indication. The authors concluded that physicians' diagnoses and
admission decisions changed frequently after CT. Diagnostic uncertainty was
alleviated.

Multiple publications (Achenbach et al, 2012; Hawkey et al, 2014; Leipsic et
al, 2011) have described the important role CT plays in screening protocols of
patients who are candidates for transcatheter aortic valve implantation (TAVI)
or transcatheter aortic valve replacement (TAVR).1,4,6 CT imaging provides
information on the suitability of the peripheral access vessels and accurate
dimensions of the involved vasculature and aortic annulus, which assists in
sizing of the prosthesis.

Published evidence, including recommendations from the American College of
Radiology (ACR), supports the use of CT of the abdomen and pelvis as a first-
line modality for the evaluation of abdominal/pelvic pathology as listed in
this policy. The published literature also supports the use of CT of the
abdomen and pelvis for treatment planning for radiation therapy as well as
guidance of interventional, diagnostic, or therapeutic procedures within the
abdomen and pelvis, including preparation for TAVI/TAVR.