Friday, April 4, 2014

Suction device for correction of pectus excavatum

Some information to file under the "good to know" category.

The suction bell  is a device that uses negative pressure (15% below atmospheric) to pull the sternum out and into a more natural position.  The principle involves repetitive intermittent use until the deformity is corrected.

In a paper by F. Haecker, the author describes a wide range of applications times, but recommends twice daily application for 30 minutes at a minimum. After the device is positioned over the deformity, the patient uses a hand pump to apply negative pressure, which instantaneously pulls the sternum up. The duration of use is limited by pain and the development of a transient subcutaneous hematoma in most of the patients.

Long term results are not available, but over a short period of use, patients experience "dramatic" results.  In the aforementioned paper, the author reports a sternal elevation of 1.5 cm in 70% of patients within a 3 month period. Again, patient dedication and level of commitment being a major determinant of outcome.  Additionally, the author suggest that the best results tend to occur in patients with milder forms of symmetric pectus excavatum.

Needless to say, this sounds like a very promising non-operative option, though the jury is still out on what is the optimal application protocol is as well as long term results and durability of the correction

Friday, March 28, 2014

The "correction index" as a measure of severity of pectus excavatum.

Pectus excavatum is a condition where the sternum and adjacent ribs develop in an abnormal way, resulting in a depression in the middle of the chest.  The consequences of the depression are mainly esthetic, but may affect lung and cardiac function (controversial evidence)
Figure 1

The Haller index (Figure 1) has been classically used as a measure of the severity of the pectus deformity, where a HI >3.25 is considered an indication for consideration for surgical correction.

An innate fault of this measurement, as St Peter et al pointed out in their paper, is the fact that this number relies heavily on the cross sectional diameter of the chest (Figure 1; measurement a), which varies between patients.  They noted that when they measured the HI in patients with a pectus deformity, there was a 45% cross-over with normal patients. Essentially, the authors suggest that the HI is not a reliable measure of severity of a pectus deformity.
Figure 2

As an alternative, the authors recommend using a measurement they referred to as the correction index (Figure 2).  Simply put, CI is the ratio of the anticipated rise in the sternal defect after bar placement (Figure 2; measurement a-b), to the maximal anterior to posterior dimension of the inner chest, multiplied by 100.

The question then becomes, what CI should be used as an indication for surgery?  The authors suggested that a 10% or higher CI reflects a pectus deformity severe enough to warrant correction.

Friday, February 21, 2014

How do Senna laxatives work?

My frustration with my inability to find a good reference that explains how Senna based laxatives work (before I prescribed it to one of my patients with HD and encopresis) was relieved by one of our fine Pedi GI folks.  She promptly sent me this paper from the deep archives of an appropriately name journal.

Here's the answer.

Senna, an anthraquinone laxative, is a glycoside that is metabolized in the GI tract into oxy-methyl anthraquinone.  OMA's (just made that up; not the official name) soften the stool by decreasing water absorption from the colon and promote colonic contraction by stimulating the Auerbach plexus of nerves.

There you go.

Thursday, February 13, 2014

In the realm of surgical oncology, biology is King!

A gem from grand rounds today:

Law of the land in surgical oncology

Biology is King
Selection is Queen
Technical maneuvers are the Prince and Princess

Occasionally the prince and princess try to
overthrow the powerful forces of the King and
Queen, sometimes with temporary apparent
victories, but usually to no long term avail.

Blake Cady, MD

Tuesday, February 11, 2014

GIST tumors in kids

Looking down at the path report that read "Wild type gastrio-intestinal stormal tumor", I had to reach deep into my memories of adult general surgery training, and all I could come up with was Gleevec. Clearly not enough to formulate a management plan for my 12 year old patient.

Off to Pubmed...

Talk about children not being just small adults!  Pediatric GISTs, it turns out, are a whole different animal.

Adult GISTs are tumors of mesenchymal origin that carry a tyrosine kinase receptor activating mutation. 85% of tumors in adults will have a mutation in either oncogenic KIT, PDGRRA, or (less commonly) BRAF. The presence of a tyrosine kinase mutation is the basis for tumor response to tyrosine kinase inhibitors such as Imatinib (Gleevec).

The pediatric counterpart, a rare entity, differs in a critical way; namely the absence of a tyrosine kinase mutation in the majority (>90%) of cases. Gastrointestinal stromal tumors with no tyrosine kinase mutation are referred to as wild type GISTs.  The absence of these mutations translates to the lack of efficacy of tyrosine kinase inhibitors such as Imatinib. Essentially, no effective neo-adjuvant or adjuvant therapy is available for WT GISTs.

Because of the rare nature of GISTs in children, we do not have a clear idea about behavior. The general impression is that these are insidious lesions, that grow slowly and have a high recurrence rate, even in the setting of complete surgical resection.

What does this mean for us, the pediatric surgeons faced with the responsibility of primum non nocere?  this is a chronic disease that needs management and not cure; more like hypertension that appendicitis.  So avoid big morbid resections if possible, and plan for this disease coming back.

Pediatric Gastrintestinal stromal tumor

Wednesday, February 5, 2014

Bilateral Wilm's Tumor

Now that the dust has settled on the move to the west coast... back to some reading.

A recent discussion about an infant with bilateral renal masses prompted a review of the COG recommendations and protocols for the management of patients with bilateral Wilm's tumor.

Obviously, the basic impetus behind the special consideration for this group of patients is the the need for preservation of functional renal tissue.  Kids with bilateral WT have several factors that contribute to potential renal failure.  These include  intrinsic disease in predisposed kidneys, loss of functional renal tissue after surgery, and injury from chemo and radiation therapy.

Historically, all pediatric patients with bilateral renal tumors have been found to have Wilm's tumor. This, along with the fact that biopsy upstages patients, increases the risk of local recurrence, and can not effectively rule out anaplasia, contributed to the current COG recommendation to proceed with chemotherapy without tissue biopsy.

Once chemotherapy is started, the pattern of tumor response after 6 and 12 weeks determines whether and how therapy is adjusted.

The COG protocol for bilateral renal masses calls for upfront three drug chemotherapy (no biopsy), with re-imaging in 6 weeks.  If, after 6 weeks, there is good response (>30% decrease in size), and the tumor is now resectable with partial renal preservation, then the surgeon proceeds with nephron sparing surgery.

For patients with partial response, but not enough for nephron sparing surgery after 6 weeks, three drug chemotherapy is continued.  At 12 weeks, all patients undergo operative resection; partial nephrectomy if made possible by further reduction in tumor size, or radical nephrectomy.

If there is no good response, then resection is needed to rule out an anaplastic component (chemotherapy needs to be adjusted) or to make sure this is not a benign lesion (further chemotherapy is unnecessary and surgical resection is curative)

COG AREN 0534 Protocol: Treatment for Patients with Bilateral, Multicentric, or 
Bilaterally-Predisposed Unilateral Wilms Tumor

Wednesday, July 24, 2013

Neo-adjuvant chemotherapy for hepatoblastoma: Do tumors shrink away from major vascular structures?


This was an eye-opening study by Murphy et al who looked at patterns of response of hepatoblastoma (both volume reduction and regression away from major vascular structures)  treated with neo-adjuvant chemotherapy.

It was eye opening for two reasons.

The first reason is that one would assume that substantial shrinkage of tumor would translate into substantial regression away from major vascular structures (and subsequently facilitate resection).  It turns out that although these tumors respond well to neo-adjuvant chemotherapy, they shrink towards major vascular structures (as if anchored to their main blood supply), and not centripetally.  In fact, the authors noted that the tumors, at most, regressed an average of 1 mm from major vascular structures.

The second, and more important eye opener, was the remark made by Dr Meyers in the discussion section of the paper.  The authors were addressing the recommendation by the COG protocol (AHEP0731) that patient with margins less than 1 cm from major vascular structures not undergo attempts at primary resection but receive neo-adjuvant chemotherapy.  The authors conculded that chemotherapy brought only a few patients closer to respectability  (because it brought only a few patients to this 1 cm level)

The misinterpretation of COG recommendations lies in the following:  The 1 cm recommended margin away from major vascular structures is intended to encourage neoadjuvant chemotherapy and avoid positive margins with attempts at primary resection.  So really, the < 1 cm margin is more an indication for neo-adjuvant chemotherapy than a contraindication for surgery.

Subsequently, once a patient has received neo-adjuvant chemotherapy, the entire < 1 cm business is out the window, and resection should be attempted if deemed possible and safe regardless of radiologic vascular margins.